Learning Resource Pack:
Building Eco Literacy in
the 21st Century
1ST SEMESTER SY 2020-2021
Nica Anne N. Roldan, MBA
Gesabel E. Impabido, ME
TARLAC AGRICULTURAL UNIVERSITY | COLLEGE OF BUSINESS AND MANAGEMENT
LEARNING RESOURCE PACK APPROVAL SHEET
Title of LRP: Building Eco Literacy in the 21st Century
Prepared by: Nica Anne N. Roldan, MBA
Class: BS Entrep 2A,2B,2C,2D, and BSTM 2A
Period of Utilization: 1st semester, SY 2020-2021
Reviewed by:
SONNY A. SANTOS
MARIBEL C. RAMALES, MBA
Chair, Curriculum Committee
Chair, IM Committee
MA. FLORA G. MARIANO, Ph.D.
Program Chair
Recommending Approval:
SILVERIO RAMON DC. SALUNSON, DBA
College Dean
CLAIRE ANNE A. OLIVARES, Ph.D.
Director, Curriculum and Instruction
Approved for Utilization:
ERNESTO A. VIRAY, JR.,Ph.D
Vice President for Academic Affairs
Micro-syllabus in BUILDING ECO LITERACY IN THE 21ST CENTURY
2
Course description
Vision
It deals with the interactions among living organisms with TAU as one of
their environment. It also concerned on life processes, the
top
500
interrelationships, behaviors, and adaptations of organisms; the universities in
movement of materials and energy through living communities; Asia
the successional development of ecosystems; and the abundance
and distribution of organisms and biodiversity in the context of
the environment.
Credit: 3-0-3
Breakthrough
Target Outcomes
Goals
At the end of the course, the students should be able to:
Anchored
on
the challenges
A. Competencies
the
1. Discuss the history and relevance of ecology to of
Sustainable
humankind.
2. Describe the concept of the ecosystem and ecosystem Development
for
management and the fundamental concepts related to Goals
inclusive
energy.
3. Identify the fundamental concepts related to energy.
growth,
4. Identify the basic types of biochemical cycles.
will:
TAU
5. Discuss the concept of limiting factors, and the 1. take lead in
properties of the population.
innovative
6. Determine the types of interaction between two teaching
species.
7. Discuss
methodologies
the ecosystem
development,
landscape and
ecology, regional ecology and the global ecology.
appropriate
technologies to
B. Skills
create an ideal
1. Make an analysis on the history of ecology and environment to
explain the relationship of ecology to humankind.
optimize
2. Apply these concepts of ecosystem and ecosystem learning;
management in everyday life.
2.
advance
C. Values
3
1. Articulate ecosystem management about the current sustainable
environmental issues.
agricultural
2. Identify the implications of these ecological concepts productivity
in the environment.
and
improve
income through
Course Content
innovation,
I. The Scope of Ecology
technology
II. The Ecosystem
generation,
III. Energy in the Ecological Systems
transfer
IV. Biogeochemical Cycle
training; and
V. Limiting and Regulatory Factors
3. use Science,
VI. Population Ecology
Technology
VII. Community Ecology
and
VIII. Ecosystem Development
Engineering
IX. Landscape Ecology
(STE)
X. Regional Ecology: Major Ecosystem Types and Biomes
effectively
XI. Global Ecology
climate change
and
for
resiliency,
adaption
and
agricultural
productivity.
Teaching and Learning Activities
Discussion,
Reflection
papers,
Instructor’s/
Video,
Ecological
Management Proposal Presentation.
Assessment Strategies
Waste Professor’s
Note/Message
1. Reading the
links and other
Reflection Paper
Discussion
Summative Tests
Ecological Waste Management Proposal Presentation
materials
will
give you better
appreciation as
a HR students.
2.
Read
all
suggested links
4
to enhance your
learning
experience.
Bask and soak
reading, while
relating
to
experiences,
and
previous
lessons in other
management
courses taken.
3.
Share
learnings,
not
answers. Share
other
learning
resources
that
you think might
be helpful.
Suggested Reading
Agar, Nicholas. (2001). Life’s Intrinsic Value: Science, Ethics,
and Nature. New York: Columbia University Press.
Allaby, Michael. (2002).Basics of Environmental Science. 2nd Ed.
New York: Taylor & Francis.
Barrett, Gary W., and Odum, Eugene P. (2004). Fundamentals of
Ecology. 5th Ed. Brooks Cole, Belmont, CA, 624 pp.
Chapin III, Stuart F., Matson, Pamela A., and Mooney, Harold A.
(2002).Principles of Terrestrial Ecosystem Ecology. SpringerVerlag New York, Inc.
Sarkar, Sahotra. (2005).Biodiversity and Environmental
Philosophy: An Introduction to the Issues. New York: Cambridge
University Press.
Wapner, Paul, and John Willoughby. (2005).‘‘The Irony of
Environmentalism: The Ecological Futility but Political
Necessity of Lifestyle Change.” Ethics & International Affairs
19/3: 77–89.
5
Grading System
Term Exam
40%
Quizzes
25%
Waste Management Proposal
25%
Attendance
10%
Total
100%
Final Grade= (Midterm grade + Final term grade)/2
1. The learning materials will be made available in the
Google classroom to make them accessible to the
students.
2. Students must comply with all the activities required
within the time frame given by the instructor/professor.
3. The students are required to participate during the
online lectures conducted by the class and behave just
like in ordinary classes. Each is expected to have read
the relevant materials provided before the scheduled
meeting in the google meet.
4.
The
students
are
bound
to
submit
all
the
requirements set in the course for proper evaluation by
the teacher. The activities may be sent through any
available online platforms such as google classroom,
messenger, FB group chat or e-mail.
5. In case of a reasonable absence during the actual
learning activity, the student can access the copy of the
IM online and can make consultation with the
concerned
teacher through
an
accessible
online
platform at a time convenient to both.
6. Cheating in all forms is prohibited. Copying the
6
assignment of your classmate is not encouraged.
Learning Resource Materials
Chapter 1: The Scope of Ecology
Lesson 1: History of ecology and relevance to humankind
Target Outcomes
7
At the end of the lesson, you are expected to:
1.
2.
3.
4.
5.
discuss the history of ecology and relevance to human kind;
illustrate the level of organizational hierarchy;
discuss the emergent property principle;
enumerate transcending functions and control processes; and
illustrate ecological interfacing and models.
Abstraction
The word ecology is derived from the Greek oikos, meaning “household,” and
logos, meaning “study.” Thus, the study of the environmental house includes all the
organisms in it and all the functional processes that make the house habitable.
Literally, then, ecology is the study of “life at home” with emphasis on “the totality or
pattern of relations between organisms and their environment,” to cite a standard dictionary definition of the word. The word economics is also derived from the Greek
root oikos. As nomics means “management,” economics translates as “the
management of the household” and, accordingly, ecology and economics should be
companion disciplines. Unfortunately, many people view ecologists and economists
as adversaries with antithetical visions.
Ecology was of practical interest early in human history. In primitive society,
all individuals needed to know their environment—that is, to understand the forces of
nature and the plants and animals around them—to survive. The beginning of civilization, in fact, coincided with the use of fire and other tools to modify the
environment. Because of technological achievements, humans seem to depend less on
the natural environment for their daily needs; many of us forget our continuing dependence on nature for air, water, and indirectly, food, not to mention waste assimilation,
recreation, and many other services supplied by nature. Also, economic systems, of
whatever political ideology, value things made by human beings that primarily benefit
the individual, but they place little monetary value on the goods and services of nature
that benefit us as a society.
Until there is a crisis, humans tend to take natural goods and services for
granted; we assume they are unlimited or somehow replaceable by technological
innovations, even though we know that life necessities such as oxygen and water may
be recyclable but not replaceable. As long as the life-support services are considered
free, they have no value in current market systems. Like all phases of learning, the
8
science of ecology has had a gradual if spasmodic development during recorded
history. The writings of Hippocrates, Aristotle, and other philosophers of ancient
Greece clearly contain references to ecological topics. However, the Greeks did not
have a word for ecology. The word ecology is of recent origin, having been first
proposed by the German biologist Ernst Haeckel in 1869. Haeckel defined ecology as
“the study of the natural environment including the relations of organisms to one
another and to their surroundings”.
Before this, during a biological renaissance in the eighteenth and nineteenth
centuries, many scholars had contributed to the subject, even though the word ecology
was not in use. For example, in the early 1700s, Antoni van Leeuwenhoek, best
known as a premier micro-scopist, also pioneered the study of food chains and
population regulation, and the writings of the English botanist Richard Bradley
revealed his understanding of biological productivity. All three of these subjects are
important areas of modern ecology.
As a recognized, distinct field of science, ecology dates from about 1900, but
only in the past few decades has the word become part of the general vocabulary. At
first, the field was rather sharply divided along taxonomic lines (such as plant ecology
and animal ecology), but the biotic community concept of Frederick E. Clements and
Victor E. Shelford, the food chain and material cycling concepts of Raymond Lindeman and G. Evelyn Hutchinson, and the whole lake studies of Edward A. Birge and
Chauncy Juday, among others, helped establish basic theory for a unified field of general ecology.
What can best be described as a worldwide environmental awareness
movement burst upon the scene during two years, 1968 to 1970, as astronauts took the
first photographs of Earth as seen from outer space. For the first time in human
history, we were able to see Earth as a whole and to realize how alone and fragile
Earth hovers in space. Suddenly, during the 1970s, almost everyone became concerned about pollution, natural areas, population growth, food and energy consumption, and biotic diversity, as indicated by the wide coverage of environmental
concerns in the popular press.
The 1970s were frequently referred to as the “decade of the environment,”
initiated by the first “Earth Day” on 22 April 1970. Then, in the 1980s and 1990s,
environmental issues were pushed into the political background by concerns for
human relations—problems such as crime, the cold war, government budgets, and
welfare. As we enter the early stages of the twenty-first century, environmental
9
concerns are again coming to the forefront because human abuse of Earth continues to
escalate. We hope that this time, to use a medical analogy, our emphasis will be on
prevention rather than on treatment, and ecology can contribute a great deal to
prevention technology and ecosystem health.
The increase in public attention had a profound effect on academic ecology.
Before the 1970s, ecology was viewed largely as a sub-discipline of biology.
Ecologists were staffed in biology departments, and ecology courses were generally
found only in the biological science curricula. Although ecology remains strongly
rooted in biology, it has emerged from biology as an essentially new, integrative
discipline that links physical and biological processes and forms a bridge between the
natural sciences and the social sciences.
Most colleges now offer campus-wide courses and have separate majors,
departments, schools, centers, or institutes of ecology. While the scope of ecology is
expanding, the study of how individual organisms and species interface and use
resources intensifies. The multilevel approach, as outlined in the next section, brings
together “evolutionary” and “systems” thinking, two approaches that have tended to
divide the field in recent years.
Level of Organizational Hierarchy
Perhaps the best way to delimit modern ecology is to consider the concept of
levels of organization, visualized as an ecological spectrum (Fig. 1). Hierarchy means
“an arrangement into a graded series”. Interaction with the physical environment
(energy and matter) at each level produces characteristic functional systems.
10
Figure 1.
A system, according to a standard definition, consists of “regularly interacting
and interdependent components forming a unified whole”. Systems containing living
(biotic) and nonliving (abiotic) components constitute bio-systems, ranging from
genetic systems to ecological systems.
Ecology is largely, but not entirely, concerned with the system levels beyond
that of the organism. In ecology, the term population, originally coined to denote a
group of people, is broadened to include groups of individuals of any one kind of
organism. Likewise, community, in the ecological sense (sometimes designated as
“biotic community”), includes all the populations occupying a given area.
The community and the nonliving environment function together as an ecological system or ecosystem. Biocoenosis and biogeocoenosis (literally, “life and
Earth functioning together”), terms frequently used in European and Russian
literature, are roughly equivalent to community and ecosystem, respectively.
Referring again to Figure 1, the next level in the ecological hierarchy is the
landscape, a term originally referring to a painting and defined as “an expanse of
11
scenery seen by the eye as one view”. In ecology, landscape is defined as a
“heterogonous area composed of a cluster of interacting ecosystems that are repeated
in a similar manner throughout”.
A watershed is a convenient landscape-level unit for large-scale study and
management because it usually has identifiable natural boundaries. Biome is a term in
wide use for a large regional or sub-continental system characterized by a major
vegetation type or other identifying landscape aspect, as, for example, the Temperate
Deciduous Forest biome or the Continental Shelf Ocean biome. A region is a large
geological or political area that may contain more than one biome—for example, the
regions of the Midwest, the Appalachian Mountains, or the Pacific Coast.
The largest and most nearly self-sufficient biological system is often
designated as the ecosphere, which includes all the living organisms of Earth
interacting with the physical environment as a whole to maintain a self-adjusting,
loosely controlled pulsing state.
Hierarchical theory provides a convenient framework for subdividing and
examining complex situations or extensive gradients, but it is more than just a useful
rank-order classification. It is a holistic approach to understanding and dealing with
complex situations, and is an alternative to the reductionist approach of seeking
answers by reducing problems to lower-level analysis. More than 50 years ago,
Novikoff (1945) pointed out that there is both continuity and discontinuity in the
evolution of the universe. Development may be viewed as continuous because it
involves never-ending change, but it is also discontinuous because it passes through a
series of different levels of organization.Thus, dividing a graded series, or hierarchy,
into components is in many cases arbitrary, but sometimes subdivisions can be based
on natural discontinuities. Because each level in the levels-of-organization spectrum
is “integrated” or interdependent with other levels, there can be no sharp lines or
breaks in a functional sense, not even between organism and population.
The individual organism, for example, cannot survive for long without its
population, any more than the organ would be able to survive for long as a selfperpetuating unit without its organism. Similarly, the community cannot exist without
the cycling of materials and the flow of energy in the ecosystem. This argument is
applicable to the previously discussed mistaken notion that human civilization can
exist separately from the natural world.
The Emergent Property Principle of Ecology
An important consequence of hierarchical organization is that as components,
or subsets, are combined to produce larger functional wholes, new properties emerge
that were not present at the level below. Accordingly, an emergent property of an
ecological level or unit cannot be predicted from the study of the components of that
level or unit.
Another way to express the same concept is non-reducible property— that is, a
property of the whole not reducible to the sum of the properties of the parts. Though
12
findings at any one level aid in the study of the next level, they never completely
explain the phenomena occurring at the next level, which must itself be studied to
complete the picture.
Two examples, one from the physical realm and one from the ecological
realm, will suffice to illustrate emergent properties. When hydrogen and oxygen are
combined in a certain molecular configuration, water is formed—a liquid with properties utterly different from those of its gaseous components.
When certain algae and coelenterate animals evolve together to produce a
coral, an efficient nutrient cycling mechanism is created that enables the combined
system to maintain a high rate of productivity in waters with a very low nutrient
content. Thus, the fabulous productivity and diversity of coral reefs are emergent
properties only at the level of the reef community.
Salt (1979) suggested that a distinction be made between emergent properties,
as defined previously, and collective properties, which are summations of the behavior of components. Both are properties of the whole, but the collective properties do
not involve new or unique characteristics resulting from the functioning of the whole
unit. Birth rate is an example of a population level collective property, as it is merely
a sum of the individual births in a designated time period, expressed as a fraction or
percent of the total number of individuals in the population.
New properties emerge because the components interact, not because the basic
nature of the components is changed. Parts are not “melted down,” as it were, but
integrated to produce unique new properties. It can be demonstrated mathematically
that integrative hierarchies evolve more rapidly from their constituents than
nonhierarchical systems with the same number of elements; they are also more
resilient in response to disturbance. Theoretically, when hierarchies are decomposed
to their various levels of subsystems, the latter can still interact and reorganize to
achieve a higher level of complexity.
Some attributes, obviously, become more complex and variable as one
proceeds to higher levels of organization, but often other attributes become less
complex and less variable as one goes from the smaller to the larger unit. Because
feedback mechanisms (checks and balances, forces and counterforces) operate
throughout, the amplitude of oscillations tends to be reduced as smaller units function
within larger units.
Statistically, the variance of the whole-system level property is less than the
sum of the variance of the parts. For example, the rate of photosynthesis of a forest
community is less variable than that of individual leaves or trees within the community, because when one component slows down, another component may speed up to
compensate. When one considers both the emergent properties and the increasing
homeostasis that develop at each level, not all component parts must be known before
the whole can be understood.
13
This is an important point, because some contend that it is useless to try to
work on complex populations and communities when the smaller units are not yet
fully understood. Quite the contrary, one may begin study at any point in the
spectrum, provided that adjacent levels, as well as the level in question, are
considered, some attributes are predictable from parts (collective properties), but
others are not (emergent properties). Ideally, a system-level study is itself a threefold
hierarchy-system, sub-system (next level below), and supra system (next level above).
For more on emergent properties, see T. F. H. Allen and Starr (1982), T. F. H. Allen
and Hoekstra (1992), and Ahl and Allen (1996).
Each bio-system level has emergent properties and reduced variance as well as
a summation of attributes of its subsystem components. The folk wisdom about the
forest being more than just a collection of trees is, indeed, a first working principle of
ecology. Although the philosophy of science has always been holistic in seeking to
understand phenomena as a whole, in recent years the practice of science has become
increasingly reductionist in seeking to understand phenomena by detailed study of
smaller and smaller components.
Laszlo and Margenau (1972) described within the history of science an
alternation of reductionist and holistic thinking (reductionism- constructionism and
atomism-holism are other pairs of words used to contrast these philosophical
approaches). The law of diminishing returns may very well be involved here, as
excessive effort in any one direction eventually necessitates taking the other (or
another) direction.
The reductionist approach that has dominated science and technology since
Isaac Newton has made major contributions. For example, research at the cellular and
molecular levels has established a firm basis for the future cure and prevention of cancers at the level of the organism. However, cell-level science will contribute very little
to the well-being or survival of human civilization if we understand the higher levels
of organization so inadequately that we can find no solutions to population overgrowth, pollution, and other forms of societal and environmental disorders.
Both holism and reductionism must be accorded equal value—and
simultaneously, not alternatively. Ecology seeks synthesis, not separation. The revival
of the holistic disciplines may be due at least partly to citizen dissatisfaction with the
specialized scientist who cannot respond to the large-scale problems that need urgent
attention. (Historian Lynn White’s 1980 essay “The Ecology of Our Science” is
recommended reading on this viewpoint.)
Accordingly, we shall discuss ecological principles at the ecosystem level,
with appropriate attention to organism, population, and community subsets and to
landscape, biome, and ecosphere supra- sets.
Fortunately, in the past 10 years, technological advances have allowed humans
to deal quantitatively with large, complex systems such as ecosystems and landscapes.
Tracer methodology, mass chemistry (spectrometry, colorimetry, and
chromatography), remote sensing, automatic monitoring, mathematic modeling,
14
geographical information systems (GIS), and computer technology are providing the
tools. Technology is, of course, a double-edged sword; it can be the means of
understanding the wholeness of humans and nature or of destroying it.
An important consequence of hierarchical organization is that as components,
or subsets, are combined to produce larger functional wholes, new properties emerge
that were not present at the level below. Accordingly, an emergent property of an
ecological level or unit cannot be predicted from the study of the components of that
level or unit.
Another way to express the same concept is non-reducible property— that is, a
property of the whole not reducible to the sum of the properties of the parts. Though
findings at any one level aid in the study of the next level, they never completely
explain the phenomena occurring at the next level, which must itself be studied to
complete the picture.
Two examples, one from the physical realm and one from the ecological
realm, will suffice to illustrate emergent properties. When hydrogen and oxygen are
combined in a certain molecular configuration, water is formed—a liquid with properties utterly different from those of its gaseous components.
When certain algae and coelenterate animals evolve together to produce a
coral, an efficient nutrient cycling mechanism is created that enables the combined
system to maintain a high rate of productivity in waters with a very low nutrient
content. Thus, the fabulous productivity and diversity of coral reefs are emergent
properties only at the level of the reef community.
Salt (1979) suggested that a distinction be made between emergent properties,
as defined previously and collective properties, which are summations of the behavior
of components. Both are properties of the whole, but the collective properties do not
involve new or unique characteristics resulting from the functioning of the whole unit.
Birth rate is an example of a population level collective property, as it is merely a sum
of the individual births in a designated time period, expressed as a fraction or percent
of the total number of individuals in the population.
New properties emerge because the components interact, not because the basic
nature of the components is changed. Parts are not “melted down,” as it were, but
integrated to produce unique new properties. It can be demonstrated mathematically
that integrative hierarchies evolve more rapidly from their constituents than
nonhierarchical systems with the same number of elements; they are also more
resilient in response to disturbance. Theoretically, when hierarchies are decomposed
to their various levels of subsystems, the latter can still interact and reorganize to
achieve a higher level of complexity.
Some attributes, obviously, become more complex and variable as one
proceeds to higher levels of organization, but often other attributes become less
complex and less variable as one goes from the smaller to the larger unit. Because
feedback mechanisms (checks and balances, forces and counterforces) operate
15
throughout, the amplitude of oscillations tends to be reduced as smaller units function
within larger units.
Statistically, the variance of the whole-system level property is less than the
sum of the variance of the parts. For example, the rate of photosynthesis of a forest
community is less variable than that of individual leaves or trees within the community, because when one component slows down, another component may speed up to
compensate. When one considers both the emergent properties and the increasing
homeostasis that develop at each level, not all component parts must be known before
the whole can be understood.
This is an important point, because some contend that it is useless to try to
work on complex populations and communities when the smaller units are not yet
fully understood. Quite the contrary, one may begin study at any point in the
spectrum, provided that adjacent levels, as well as the level in question, are
considered, some attributes are predictable from parts (collective properties), but
others are not (emergent properties). Ideally, a system-level study is itself a threefold
hierarchy-system, sub-system (next level below), and supra system (next level above).
For more on emergent properties, see T. F. H. Allen and Starr (1982), T. F. H. Allen
and Hoekstra (1992), and Ahl and Allen (1996).
Each bio-system level has emergent properties and reduced variance as well as
a summation of attributes of its subsystem components. The folk wisdom about the
forest being more than just a collection of trees is, indeed, a first working principle of
ecology. Although the philosophy of science has always been holistic in seeking to
understand phenomena as a whole, in recent years the practice of science has become
increasingly reductionist in seeking to understand phenomena by detailed study of
smaller and smaller components.
Laszlo and Margenau (1972) described within the history of science an
alternation of reductionist and holistic thinking (reductionism- constructionism and
atomism-holism are other pairs of words used to contrast these philosophical
approaches). The law of diminishing returns may very well be involved here, as
excessive effort in any one direction eventually necessitates taking the other (or
another) direction.
The reductionist approach that has dominated science and technology since
Isaac Newton has made major contributions. For example, research at the cellular and
molecular levels has established a firm basis for the future cure and prevention of cancers at the level of the organism. However, cell-level science will contribute very little
to the well-being or survival of human civilization if we understand the higher levels
of organization so inadequately that we can find no solutions to population overgrowth, pollution, and other forms of societal and environmental disorders.
Both holism and reductionism must be accorded equal value—and
simultaneously, not alternatively. Ecology seeks synthesis, not separation. The revival
of the holistic disciplines may be due at least partly to citizen dissatisfaction with the
specialized scientist who cannot respond to the large-scale problems that need urgent
16
attention. (Historian Lynn White’s 1980 essay “The Ecology of Our Science” is
recommended reading on this viewpoint.)
Accordingly, we shall discuss ecological principles at the ecosystem level,
with appropriate attention to organism, population, and community subsets and to
landscape, biome, and ecosphere supra- sets.
Fortunately, in the past 10 years, technological advances have allowed humans
to deal quantitatively with large, complex systems such as ecosystems and landscapes.
Tracer methodology, mass chemistry (spectrometry, colorimetry, and
chromatography), remote sensing, automatic monitoring, mathematic modeling,
geographical information systems (GIS), and computer technology are providing the
tools. Technology is, of course, a double-edged sword; it can be the means of
understanding the wholeness of humans and nature or of destroying it.
Transcending Functions and Control Processes of Ecology
Whereas each level in the ecological hierarchy can be expected to have unique
emergent and collective properties, there are basic functions that operate at all levels.
Examples of such transcending functions are behaviour, development, diversity, energetics, evolution, integration, and regulation. Some of these (energetics, for example)
operate the same throughout the hierarchy, but others differ in modus operandi at
different levels. Natural selection evolution, for example, involves mutations and
other direct genetic interactions at the organism level but indirect co-evolutionary and
group selection processes at higher levels.
It is especially important to emphasize that although positive and negative
feedback controls are universal, from the organism down, control is set point, in that it
involves very exacting genetic, hormonal, and neural controls on growth and development, leading to what is often called homeostasis.
The term homeorhesis, from the Greek meaning “maintaining the flow,” has
been suggested for this pulsing control. In other words, there are no equilibriums at
the ecosystem and ecosphere levels, but there are pulsing balances, such as between
production and respiration or between oxygen and carbon dioxide in the atmosphere.
Failure to recognize this difference in cybernetics (the science dealing with
mechanisms of control or regulation) has resulted in much confusion about the
realities of the so-called “balance of nature.”
Ecological Interfacing
17
Because ecology is a broad, multilevel discipline, it interfaces well with
traditional disciplines that tend to have more narrow focus. During the past decade,
there has been a rapid rise of interface fields of study accompanied by new societies,
journals, symposium volumes, books—and new careers. Others that are receiving a
great deal of attention, especially in resource management, are agro-ecology,
biodiversity, conservation ecology, ecological engineering, ecosystem health,
ecotoxicology, environmental ethics, and restoration ecology.
In the beginning, an interface effort enriches the disciplines being interfaced.
Lines of communication are established, and the expertise of narrowly trained “experts” in each field is expanded. However, for an interface field to become a new discipline, something new has to emerge, such as a new concept or technology. The concept of nonmarket goods and services, for example, was a new concept that emerged
in ecological economics, but that initially neither traditional ecologists nor economists
would put in their textbooks.
Natural capital is defined as the benefits and services supplied to human
societies by natural ecosystems, or provided “free of cost” by unmanaged natural
systems. These benefits and services include purification of water and air by natural
processes, decomposition of wastes, maintenance of biodiversity, control of insect
pests, pollination of crops, mitigation of floods, and provision of natural beauty and
recreation, among others.
Economic capital is defined as the goods and services provided by humankind,
or the human workforce, typically expressed as the gross national product (GNP).
Gross national product is the total monetary value of all goods and services provided
in a country during one year. Natural capital is typically quantified and expressed in
units of energy, whereas economic capital is expressed in monetary units.
Only in recent years has there been an attempt to value the world’s ecosystem
services and natural capital in monetary terms. Costanza, d’Arge, et al. (1997)
estimated this value to be in the range of 16 to 54 trillion U.S. dollars per year for the
entire biosphere, with an average of 33 trillion U.S. dollars per year. Thus it is wise to
protect natural ecosystems, both ecologically and economically, because of the
benefits and services they provide to human societies.
Utilization of Learning
18
Answer the following questions;
1.
2.
3.
4.
5.
How the history of ecology is relevant to human kind?
What are the levels of organizational hierarchy?
Explain the emergent property principle.
What is transcending functions and control processes?
What is ecological interfacing?
Supplementary Materials
https://www.ecologyessays.com/essay/ecology-compilation-of-essays-onecology/13305
Essentials of Ecology eBooks (Available in Google Classroom)
Lesson 2: Management and Concept of Ecosystem
19
Target Outcomes
At the end of the lesson, you are expected to:
1.
2.
3.
4.
5.
6.
7.
8.
discuss management and the concept of ecosystem;
identify the trophic structure of the ecosystem;
discuss gradients and eco tones;
list examples of ecosystems and ecosystem diversity;
discuss biological control of the geochemical environment;
explain microcosms, mesocosms, and macrocosms;
discuss ecosystems cybernetics and techno-ecosystems; and
illustrate the concept of the ecological footprint and classification of
ecosystems.
Abstraction
Living (biotic) organisms and their nonlivirng (abiotic) environment are
inseparably interrelated and interact with each other. Any unit that includes all the
organisms (the biotic community) in a given area interacting with the physical
environment so that a flow of energy leads to clearly defined biotic structures and
cycling of materials between living and nonliving components is an ecological system
or ecosystem. It is more than a geographical unit (or eco-region); it is a functional
system unit with inputs with and outputs, and boundaries that can be either natural or
arbitrary.
The ecosystem is the first unit in the ecological hierarchy that is complete-that
has all the components (biological and physical) necessary for survival Accordingly,
it is the basic unir around which to organize both theory and practice in ecology.
Furthermore, as the short comings of the “peacemeal”, short term and technological
and economic approaches dealing with complex problems become ever more evident
with each passing year, management at this level (ecosystem management) emerges
as the challenge for the future.
The term ecosystem was first proposed in 1935 by the British ecologist Sir
Arthur G Tansley (Tansley 1935). Allusions to the idea of the unity of organisms and
20
environment (and the oneness of humans and nature) can be found as far back in
written history as one might care to look. Not until the late 1800s, however, did
formal statements begin to appear, interesting enough, in a parallel manner in the
American, European, and Russian ecological literature. Thus, Karl Mobius in 1877
wrote (in German) about the community of organisms in an oyster reef as a
"biocoenosis”, and in1887 S.A. Forbes, an American, wrote his classic essay “The
Lake as a Microcosm”. The pioneering Russian, V. V, Dokuchaev (1846-1903), and
his chief discipline, G.F. Morozov, emphasized the concept of the “biocoenosis”, a
term later expanded by Russian, ecologists to "geobiocoenosis”, (Sukachev 1944).
Not only biologists but also physical scientists and social scientists began to
consider the idea that both nature and human societies function as systems. In 1925
Physical chemist A.J. Lotka wrote in a book entitled Elements of Physical Biology
that the organic and inorganic worlds function-as a single system to such an extent
that it is impossible to understand either part without understanding the whole. It is
significant that a biologist (Tansley) and a physical scientist (Lotka) independently
and at about the same time came up with the idea of the ecological system. Because
Tanslev coined the word ecosystem and it caught on, he received most of the credit
which perhaps should be shared with Lotka.
One of the universal features of all ecosystems whether terrestrial, freshwater,
marine, or human-engineered (for example, agricultural)-is the interaction of the
autotrophic and heterotrophic components. The organisms responsible for the
processes are partially separated in space; the greatest autotrophic metabolism occurs
in the upper "green belt" stratum, where light -energy is available. The most intensive
heterotrophic metabolism occurs in the lower "brown belt," where organic matter
accumulates in soils and sediments. Also, the basic functions are partially, separated
in time, as there may be a considerable delay in the heterotrophic use of the product
autotrophic organisms. For example, photosynthesis predominates in the canopy of a
forest ecosystem. Only a part, often only a small part of the photosynthate is
immediately and directly used by the plant and by herbivore and parasites that feed on
foliage and other actively growing plant tissue.
The biosphere is characterized.by a series of gradients, or zonation, of physical
factors. Examples are temperature gradients from the Arctic or Antarctic to the
Tropics and from mountaintop to vailey, moisture gradients from wet to dry along
ma1or weather systems; and depth gradients from shore to bottom in bodres of water.
21
Environmental conditions, including the organisms adapted to these conditions,
‘change gradually along a gradient, but often there are points of abrupt change, known
as ectones. An ecotone is created by the juxtaposition of different habitats, or
ecosystem types. The concept assumes the existence of active interaction between two
or more ecosystems (or patches within ecosystems), which results in the ecotone
having properties that do not exist in either of the adjacent ecosystems (Naiman and
Decamps 1990)
Trophic Structure of the Ecosystem
Tropic structure is a tiered structure of the organism in an ecosystem, with
each level representing those organisms that share a similar function and food source.
Trophic structure diagrams also depict the energy transfer from on trophic level to the
next. By organizing the estuary into a trophic structure, we are given an indication of
the productivity of the estuary. Productivity is basically the ability of the estuary to
yield organic matter. A productive estuary is one that has high diversity, high survival
rates, little to no invasive species, and whose organisms continually carry out life
processes; in other words, the estuary is sustainable. Freshwater inflows are
fundamentally linked to estuarine productivity.
An example of a trophic structure is shown below. This trophic structure looks
at the aquatic ecosystem from a bottom up point of view. The bottom tier organisms,
or primary producers, are the most energy efficient, while the top tier, or top
predators, are the least energy efficient. Primary producers produce their own food,
making them more energy efficient, while top fish or predators require many
organisms, making them less energy efficient. Another way to say this is that
predators have a much higher energy demand than do phytoplankton. The
trophic structure in the figure below shows an ecosystem functioning by
interrelationships and life processes. Freshwater inflows balance the
estuaries by providing hydrological requirements for the organisms.
22
The Gradients and Eco tones
Eco tones are areas of transition between ecological communities,
ecosystems, or ecological regions (such as Mediterranean and desert). Ecotones
often occur along ecological gradients. Such gradients are created as a result of
spatial shifts in elevation, climate, soil, and many other environmental factors.
Ecotones commonly coincide with areas of sharp climatic transition along
environmental gradients. They occur at multiple spatial scales, from continentalscale transitions between major biomes to small-scale ecotones where local
vegetation communities and microhabitats coincide. They show a diversity of
boundary types that range from natural boundaries (e.g., altitudinal, latitudinal
transitions) to human-generated ecotones (e.g., forest clear-cut edges or urban
ecotones). Ecotones have been studied in the past four decades in an ecological
23
context and in recent years are receiving increasing attention in the context of
biodiversity conservation. Various studies have shown that species richness and
abundances tend to peak in ecotonal areas, though exceptions to these patterns
occur. Ecotones are “natural laboratories” for studying a range of evolutionary
processes, such as the process by which new species form, also termed speciation.
Some researchers argue that ecotones deserve high-conservation investment,
potentially serving as speciation and biodiversity centers. Because ecotones are
often small in size and relatively rich in biodiversity, conservation efforts in these
areas may prove to be an efficient and cost-effective conservation strategy.
The Ecosystems and Ecosystem Diversity
An ecosystem is a community of living organisms in conjunction with
the nonliving
[2]
components of
their
environment,
interacting
as
a system.
These biotic and abiotic components are linked together through nutrient cycles and
energy flows.[3] Energy enters the system through photosynthesis and is incorporated
into plant tissue. By feeding on plants and on one another, animals play an important
role in the movement of matter and energy through the system.
Ecosystem
a geographical
diversity deals
location and
its
with
overall
the
variations
impact
on
in ecosystems within
human
existence
and
the environment. Ecosystem diversity addresses the combined characteristics
of biotic properties (biodiversity) and abiotic properties (geodiversity). It is the
variation in the ecosystems found in a region or the variation in ecosystems over the
whole planet. Ecological diversity includes the variation in both terrestrial and aquatic
ecosystems. Ecological diversity can also take into account the variation in
the complexity of a biological community, including the number of different niches,
the number of trophic levels and other ecological processes. An example of ecological
diversity on a global scale would be the variation in ecosystems, such
as deserts, forests, grasslands, wetlands and oceans. Ecological diversity is the largest
scale of biodiversity, and within each ecosystem, there is a great deal of
both species and genetic diversity.
Biological Control of the Geochemical Environment
Individual organisms not only adapt to the physical environment but, by their
concerted action in ecosystems, they also adapt the geochemical environment to their
24
biological needs. The fact that the chemistry of the atmosphere, the strongly buffered
physical environment of Earth, and the presence of a diversity of aerobic life are
utterly different from conditions on any other planet in this solar system has led to the
Gaia
hypothesis.
The
Gaia
hypothesis
holds
that
organisms,
especially
microorganisms, have evolved with the physical environment to provide an intricate,
self-regulatory control system that keeps conditions favorable for life on Earth
(Lovelock I979)
Although most of us know that the abiotic environment (physical factors)
controls the activities of organisms, not all of us recognize that organisms influence
and control the abiotic environment in many important ways. The physical and
chemical natures of inert materials are constantly being changed by organisms,
especially bacteria and fungi, which return new compounds and energy sources to the
environment. The actions of marine organisms largely determine the content of the
sea and of its bottom oozes. Plants growing on a sand dune build up a soil radically
different from the original substrate. A South Pacific coral atoll is a striking example
of how organisms modify the abiotic environment. The extension of biological
controls to the global level rs the basis for James Love locks Gaia hypothesis (from
Goia, the Greek name for the Earth goddess). Lovelock, a physical scientist, inventor,
and engineer, teamed up with microbiologist Lynn Margulis to explain the Gaia
hypothesis in a series of articles and books (Lovelock 1979,1988; Lovelock and
Margulis I973; Margulis and Lovelock 1974, Lovelock and Epton I975, Margulis and
Sagan 1997). They concluded that the atmosphere of Earth, with its unique highoxygen/low-carbon dioxide content, and the moderate temperature and pH conditions
on the surface of Earth, cannot be accounted for without the critical buffering
activities of early life-forms and the continued coordinated activity of plants and
microbes that dampen the fluctuations in physical factors that would occur in the
absence of well-organized living systems. For example, ammonia produced by
microorganisms maintains a pH in soils and sediments that is favorable to a wide
variety of life. Without this organisms output, the pH of soils on Earth could become
so low that it would preclude all but a very few kinds of organisms.
25
Microcosms, Mesocosms, and Macrocosms
Little self-contained worlds, or microcosms, in bottles or other containers,
such as aquaria, can simulate in miniature the nature of ecosystems. Such containers
can be considered micro ecosystems. Large experimental tanks or outdoor enclosures,
termed mesocosms ("midsized worids"), are more realistic experimental models
because they are subjected to naturally pulsing environmental factors, such as light
and temperature, and can contain larger organisms with more complex life histories.
The planet Earth, large watersheds, or natural landscapes, termed macrocosms (the
natural or "great" world), are the natural systems used for baseline or "control"
measurements.
A self-contained mesocosm including humans, called Biosphere-2, was a first
attempt to build a bio regenerative enclosure such as might someday be constructed
on the Moon or nearby planets. Spacecraft and space stations as now operated are not
self-contained and can remain in space only a short time unless they are frequently
resupplied from Earth. The characteristics and processes of the naturally evolved
biosphere need to be coupled with the human-designed industrial "synthesphere"
(Severinghaus et al. L994) in order to design systems that mimic ecosystem
sustainability.
Ecosystems cybernetics and techno-ecosystems
Cybernetics is a trans disciplinary approach for exploring regulatory systems
—their structures, constraints, and possibilities. Norbert Wiener defined cybernetics
in 1948 as "the scientific study of control and communication in the animal and the
machine".
Cybernetics is applicable when a system being analysed incorporates a closed
signalling loop—originally referred to as a "circular causal" relationship—that is,
where action by the system generates some change in its environment and that change
is reflected in the system in some manner (feedback) that triggers a system change.
Cybernetics is relevant to, for example, mechanical, physical, biological, cognitive,
and social systems. The essential goal of the broad field of cybernetics is to
understand and define the functions and processes of systems that have goals and that
26
participate in circular, causal chains that move from action to sensing to comparison
with desired goal, and again to action. Its focus is how anything (digital, mechanical
or biological) processes information, reacts to information and changes or can be
changed to better accomplish the first two tasks. Cybernetics includes the study
of feedback, black
boxes and
derived
concepts
such
as communication and control in living
organisms, machines and organizations including self-organization.
Concepts
studied
by cyberneticists include,
but
are
not
limited
to: learning, cognition, adaptation, social
control, emergence, convergence, communication, efficiency, efficacy,
and connectivity. In cybernetics these concepts (otherwise already objects of study in
other disciplines such as biology and engineering) are abstracted from the context of
the specific organism or device.
The
word cybernetics comes
from Greek
(kybernētikḗ),
meaning
"governance", i.e., all that are pertinent to (kybernáō), the latter meaning "to steer,
navigate or govern", hence (kybérnēsis), meaning "government", is the government
while (kybernḗtēs) is the governor or "helmsperson" of the "ship". Contemporary
cybernetics began as an interdisciplinary study connecting the fields of control
systems, electrical
network
theory, mechanical
engineering, logic
modelling, evolutionary biology, neuroscience, anthropology, and psychology in the
1940s, often attributed to the Macy Conferences. During the second half of the 20th
century cybernetics evolved in ways that distinguish first-order cybernetics (about
observed systems) from second-order cybernetics (about observing systems). More
recently there is talk about a third-order cybernetics (doing in ways that embraces first
and second-order).
Studies in cybernetics provide a means for examining the design and function
of any system, including social systems such as business management and
organizational
learning,
including
for
the
purpose
of
making
them
more efficient and effective. Fields of study which have influenced or been influenced
by cybernetics include game theory, system theory (a mathematical counterpart to
cybernetics), perceptual
control
(especially neuropsychology, behavioural
theory, sociology,
psychology
psychology, cognitive
psychology), philosophy, architecture, and organizational theory. System dynamics,
27
originated with applications of electrical engineering control theory to other kinds
of simulation models (especially business systems) by Jay Forrester at MIT in the
1950s, is a related field.
The concept of techno ecosystems has been pioneered by ecologists Howard
T. Odum and Zev Naveh. Techno ecosystems interface with and are competitive
toward natural systems. They have advanced technology (or techno diversity) moneybased market economies and have a large ecological footprints. Techno ecosystems
have far greater energy requirements than natural ecosystems, excessive water
consumption, and release toxic and eutrophication chemicals. Other ecologists have
defined the extensive global network of road systems as a type of techno ecosystem.
Concept of the ecological footprint and classification of ecosystems
The ecological footprint is a method promoted by the Global Footprint
Network to measure human demand on natural capital, i.e. the quantity of nature it
takes to support people or an economy. It tracks this demand through an ecological
accounting system. The accounts contrast the biologically productive area people use
for their consumption to the biologically productive area available within a region or
the world (bio capacity, the productive area that can regenerate what people demand
from nature). In short, it is a measure of human impact on the environment.
Footprint and bio capacity can be compared at the individual, regional,
national or global scale. Both footprints and bio capacity change every year with
number of people, per person consumption, efficiency of production, and productivity
of ecosystems. At a global scale, footprint assessments show how big humanity's
demand is compared to what Earth can renew. Global Footprint Network estimates
that, as of 2014, humanity has been using natural capital 1.7 times as fast as Earth can
renew it, which they describe as meaning humanity's ecological footprint corresponds
to 1.7 planet Earths.
Ecological footprint analysis is widely used around the world in support
of sustainability assessments.[6] It enables people to measure and manage the use of
resources
throughout
the
individual lifestyles, goods
economy
and
and
services,
explore
the
sustainability
organizations, industry
of
sectors,
neighbourhoods, cities, regions and nations.
28
The ecosystems are classified into many types and are classified based on a
number of factors. We will discuss major types of ecosystems and will try and
understand on what basis these classifications are done. It is also essential to know
the different factors which differentiate the ecosystems from one another.
Ecosystems can generally be classified into two classes such as natural and
artificial. Artificial ecosystems are natural regions affected by man’s interferences.
They are artificial lakes, reservoirs, townships, and cities. Natural ecosystems are
basically classified into two major types. They are aquatic ecosystem and terrestrial
ecosystem.
Types of Natural Ecosystem
An ecosystem is a self-contained unit of living things and their non-living
environment. The following chart shows the types of Natural Ecosystem −
Biotic (Living Components)
Biotic components in ecosystems include organisms such as plants, animals, and
microorganisms. The biotic components of ecosystem comprise of the following;

Producers or Autotrophs
29

Consumers or Heterotrophs

Decomposers or Detritus
Abiotic (Non-living Components)
Abiotic components consist of climate or factors of climate such as
temperature, light, humidity, precipitation, gases, wind, water, soil, salinity,
substratum, mineral, topography, and habitat. The flow of energy and the cycling of
water and nutrients are critical to each ecosystem on the earth. Non-living
components set the stage for ecosystem operation.
Aquatic Ecosystem
An ecosystem which is located in a body of water is known as an aquatic
ecosystem. The nature and characteristics of the communities of living or biotic
organisms and non-living or abiotic factors which interact with and interrelate to one
another are determined by the aquatic surroundings of their environment they are
dependent upon.
Aquatic ecosystem can be broadly classified into Marine Ecosystem and Freshwater
Ecosystem.
Marine Ecosystem
These ecosystems are the biggest of all ecosystems as all oceans and their
parts are included in them. They contain salt marshes, intertidal zones, estuaries,
lagoons, mangroves, coral reefs, the deep sea, and the sea floor.
Marine ecosystem has a unique flora and fauna, and supports a vast kingdom
of species. These ecosystems are essential for the overall health of both marine and
terrestrial environments.
Salt marshes, seagrass meadows, and mangrove forests are among the most
productive ecosystem. Coral reef provides food and shelter to the highest number of
marine inhabitants in the world. Marine ecosystem has a large biodiversity.
Freshwater Ecosystem
30
Freshwater ecosystem includes lakes, rivers, streams, and ponds. Lakes are
large bodies of freshwater surrounded by land.
Plants and algae are important to freshwater ecosystem because they provide
oxygen through photosynthesis and food for animals in this ecosystem. Estuaries
house plant life with the unique adaptation of being able to survive in fresh and salty
environments. Mangroves and pickle weed are examples of estuarine plants.
Many animals live in freshwater ecosystem. Freshwater ecosystem is very
important for people as they provide them water for drinking, energy and
transportation, recreation, etc.
Terrestrial Ecosystem
Terrestrial ecosystems are those ecosystems that exist on land. Water may be
present in a terrestrial ecosystem but these ecosystems are primarily situated on land.
These ecosystems are of different types such as forest ecosystem, desert ecosystem,
grassland and mountain ecosystems.
Terrestrial ecosystems are distinguished from aquatic ecosystems by the lower
availability of water and the consequent importance of water as a limiting factor.
These are characterized by greater temperature fluctuations on both diurnal and
seasonal basis, than in aquatic ecosystems in similar climates.
Availability of light is greater in terrestrial ecosystems than in aquatic
ecosystems because the atmosphere is more transparent on land than in water.
Differences in temperature and light in terrestrial ecosystems reflect a completely
different flora and fauna.
31
Utilization of Learning
Answer the following questions;
1. What is eco system management?
2. Explain the concept of ecosystem?
3. Explain trophic structure of the ecosystem.
4. What is a gradient?
5. What is eco tones?
6. Give examples of ecosystems and ecosystem diversity.
7. Explain the biological control of the geochemical environment.
8. What is microcosms, mesocosms, and macrocosms?
9. What is ecosystems cybernetics and techno-ecosystems?
10. Explain the concept of the ecological footprint.
11. What are the different classifications of ecosystems?
Supplementary Materials
https://www.freshwaterinflow.org
https://link.springer.com
https://en.wikipedia.org/wiki/Ecosystem_diversity
https://en.wikipedia.org/wiki/Ecosystem_diversity
Essentials of Ecology eBooks (Available in Google Classroom)
https://en.wikipedia.org/wiki/Cybernetics
https://www.tutorialspoint.com/environmental
32
Chapter 2
Energy in Ecological System
Lesson 1: Fundamental concepts of energy
Target Outcomes
At the end of the lesson, you are expected to:
1.
2.
3.
4.
5.
6.
7.
8.
9.
explain the fundamental concepts of energy;
explain Solar Radiation and the Energy Environment;
discuss the concept of productivity;
explain energy partitioning in Food Chains and Food Webs;
explain energy quality;
discuss metabolism and Size of individuals;
discuss the concepts of carrying capacity and sustainability;
illustrate the energy-based classification of ecosystems; and
discuss energy futures.
Abstraction
Energy is defined as the ability to do work. The behavior of energy is
described by the following laws: The first law of thermodynamics or the law of
conservation of energy, states that energy may be transformed from one form into
another but is neither created nor destroyed. Light, for example, is a form of energy; it
can be transformed into work, heat, or potential energy of food, depending on the
situation, but none of it is destroyed. The second law of thermodynamics, or the law
of entropy, may be stated in several ways, including the following: No process
involving an energy transformation will spontaneously occur unless there is a
degradation of energy from a concentrated form into a dispersed form. For example,
heat in a hot object will spontaneously tend to become dispersed into the cooler
surroundings. The second law of thermodynamics may also be stated as follows:
33
Because some energy is always dispersed into unavailable heat energy, no
spontaneous transformation of energy (sunlight, for example) into potential energy
(protoplasm, for example) is 100 percent efficient. Entropy (from en = "irt'' and trape :
"transformation') is a measure of the unavailable energy resulting from
transformations; the term is also used as a general index of the disorder associated
with energy degradation.
Organisms, ecosystems, and the entire ecosphere possess the following
essential thermodynamic characteristics: They can create and maintain a high state of
internal order, or a condition of low entropy (a low amount of disorder). Low entropy
is achieved by continually and efficiently dissipating energy of high utility (light or
food, for example) into energv of low utility (heat, for example). In the ecosystem,
order in a complex biomass structure is maintained by the total community
respiration, which continually "pumps out disorder." Accordingly, ecosystems and
organisms are open, non-equilibrium thermodynamic systems that continuously
exchange energy and matter with the environment to decrease internal entropy, but
increase external entropy (thus conforming to the laws of thermodynamics).
Solar radiation, often called the solar resource, is a general term for the
electromagnetic radiation emitted by the sun. Solar radiation can be captured and
turned into useful forms of energy, such as heat and electricity, using a variety of
technologies. However, the technical feasibility and economical operation of these
technologies at a specific location depends on the available solar resource.
BASIC PRINCIPLES
Every location on Earth receives sunlight at least part of the year. The amount of solar
radiation that reaches any one spot on the Earth's surface varies according to:

Geographic location

Time of day

Season

Local landscape

Local weather.
Because the Earth is round, the sun strikes the surface at different angles, ranging
from 0° (just above the horizon) to 90° (directly overhead). When the sun's rays are
34
vertical, the Earth's surface gets all the energy possible. The more slanted the sun's
rays are, the longer they travel through the atmosphere, becoming more scattered and
diffuse. Because the Earth is round, the frigid polar regions never get a high sun, and
because of the tilted axis of rotation, these areas receive no sun at all during part of
the year.
The Earth revolves around the sun in an elliptical orbit and is closer to the sun during
part of the year. When the sun is nearer the Earth, the Earth's surface receives a little
more solar energy. The Earth is nearer the sun when it is summer in the southern
hemisphere and winter in the northern hemisphere. However, the presence of vast
oceans moderates the hotter summers and colder winters one would expect to see in
the southern hemisphere as a result of this difference.
The 23.5° tilt in the Earth's axis of rotation is a more significant factor in determining
the amount of sunlight striking the Earth at a particular location. Tilting results in
longer days in the northern hemisphere from the spring (vernal) equinox to the fall
(autumnal) equinox and longer days in the southern hemisphere during the other 6
months. Days and nights are both exactly 12 hours long on the equinoxes, which
occur each year on or around March 23 and September 22.
Countries such as the United States, which lie in the middle latitudes, receive more
solar energy in the summer not only because days are longer, but also because the sun
is nearly overhead. The sun's rays are far more slanted during the shorter days of the
winter months. Cities such as Denver, Colorado, (near 40° latitude) receive nearly
three times more solar energy in June than they do in December.
The rotation of the Earth is also responsible for hourly variations in sunlight. In the
early morning and late afternoon, the sun is low in the sky. Its rays travel further
through the atmosphere than at noon, when the sun is at its highest point. On a clear
day, the greatest amount of solar energy reaches a solar collector around solar noon.
DIFFUSE AND DIRECT SOLAR RADIATION
As sunlight passes through the atmosphere, some of it is absorbed, scattered, and
reflected by:
35

Air molecules

Water vapour

Clouds

Dust

Pollutants

Forest fires

Volcanoes.
This is called diffuse solar radiation. The solar radiation that reaches the
Earth's surface without being diffused is called direct beam solar radiation. The sum
of the diffuse and direct solar radiation is called global solar radiation. Atmospheric
conditions can reduce direct beam radiation by 10% on clear, dry days and by 100%
during thick, cloudy days.
MEASUREMENT
Scientists measure the amount of sunlight falling on specific locations at
different times of the year. They then estimate the amount of sunlight falling on
regions at the same latitude with similar climates. Measurements of solar energy are
typically expressed as total radiation on a horizontal surface,or as total radiation on a
surface tracking the sun.
Radiation data for solar electric (photovoltaic) systems are often represented as
kilowatt-hours per square meter (kWh/m2). Direct estimates of solar energy may also
be expressed as watts per square meter (W/m2).
Radiation data for solar water heating and space heating systems are usually
represented in British thermal units per square foot (Btu/ft2).
DISTRIBUTION
The solar resource across the United States is ample for photovoltaic (PV)
systems because they use both direct and scattered sunlight. Other technologies may
be more limited. However, the amount of power generated by any solar technology at
a particular site depends on how much of the sun's energy reaches it. Thus, solar
36
technologies function most efficiently in the south-western United States, which
receives the greatest amount of solar energy.
There are several different factors that control the primary productivity of
energy and biomass flow. Energy flow is the amount of energy that moves through a
food chain. The energy input, or energy that enters the ecosystem, is measured in
Joules or calories. Accordingly, the energy flow is also called calorific flow. In the
study of energy flow, ecologists try to quantify the importance of different species and
feeding relationships.
The largest source of energy for an ecosystem is the sun. Energy that is not
used in an ecosystem is eventually lost as heat. Energy and nutrients are passed
around through the food chain, when one organism eats another organism. Any
energy remaining in a dead organism is consumed by decomposers. Nutrients can be
cycled through an ecosystem but energy is simply lost over time.
An example of energy flow in an ecosystem would begin with the autotrophs
that take energy from the sun. Herbivores then feed on the autotrophs and change the
energy from the plant into energy that they can use. Carnivores subsequently feed on
the herbivores and, finally, other carnivores prey on the carnivores.
In each case, energy is passed on from one trophic level to the next trophic
level and each time some energy is lost as heat into the environment. This is due to
the fact that each organism must use some energy that they received from other
organisms in order to survive. The top consumer of a food chain will be the organism
that receives the least amount of energy.
Hairston and Hairston (1993)^ , believe that there is a cause and effect
relationship that results in any given trophic structure. Specifically, they state that it is
trophic structure, rather than energetics that controls the amount of energy consumed
at each trophic level and that "ecological efficiencies" are the product of a trophic
structure, not a determining factor. Further, they state that trophic structure is instead
the result of competition and predator-prey interactions. It is important to remember
that many species may occupy each trophic level and are so subject to interspecific
37
competition. This is especially true for producers, carnivores, and decomposers
(Hairston, Smith, and Slobodkin, 1960)^ .
Energy is the ability to do work. Life manifests itself in energy changes, subject to
the laws of thermodynamics. Ecosystems exist and operate by virtue of a flow of
energy through the components of the system and thermodynamics (the movement of
energy) forms the very basis of the biosphere organizing principles.Before proceeding
into the relationship between ecology and thermodynamics, it is necessary to build a
basic understanding of the physics of energetics, simply a further demonstration of the
fact that ecology is multidisciplinary, requiring of its students a broad knowledge in
all sciences.

Read Energy - Follow links and cover details only as necessary to gain a
basic understanding

Read Laws of Thermodynamics - Read the expanded articles as needed to
understand these basic principles of energy changes

Read Principles of Energetics - You will find a constellation of related
articles, including several with an ecological focus. You may wish to visit
all of these to foster a deeper understanding
Although several sources of energy are available for exploitation on earth (e.g.,
geothermal, nuclear decay), the most significant is solar energy. Light and other
radiation streaming out from the sun strikes the earth 93 million miles distant,
providing energy to the atmosphere, the seas, and the land, warming objects that
absorb this energy; that is, radiant energy is converted to heat energy (molecular
motion). Differential heating causes winds and currents in the air and water, the
heat energy becoming kinetic energy of motion. Warming results in evaporation
of water into the atmosphere, setting up the hydrologic cycle, the lifting of water
into the atmosphere becoming potential energy that will convert to kinetic energy
when the water begins to flow back downhill. However, the most significant solar
energy driven process with respect to living systems is that of photosynthesis.
Light energy is converted by photosynthesizing cells into a form of potential
energy held in the chemical bonds of organic compounds. Organisms require both
the substance and the stored energy of chemical compounds to function and grow,
38
and eventually reproduce. Substance to provide the building blocks of cellular
(and extracellular) components that comprise structure, and energy to move
substances around, affect chemical reactions, and carry out all manner of
intracellular and organismal processes.
When it comes to the flow of energy in ecosystems there are two types of
organisms: producers and consumers. Plants are a common example of
producers in all populations. They are able to convert carbon dioxide into oxygen
and glucose, a common sugar consumed by most organisms. They do this through
a process called photosynthesis which allows the plants to use sunlight as a source
of energy. Producers convert energy from the environment into chemical energy
in the form of carbon to carbon bonds. A classic example is the one previously
mentioned where the plants convert CO2 to O2 and glucose.
The second type of organism is the consumer. Consumers are unable to make
chemical energy the way plants do and have to use metabolic processes to get
energy from carbon to carbon bonds, which is called respiration. Respiration
breaks the carbon to carbon bonds and combines them with oxygen to make
carbon dioxide. The energy released is used to help organisms move their muscles
or as heat. Energy cannot be reused once it has been lost.
In ecology, the term productivity refers to the rate of generation of biomass in
an ecosystem, usually expressed in units of mass per volume (unit surface) per
unit of time, such as grams per square metre per day (g m−2 d−1). The unit of mass
can relate to dry matter or to the mass of generated carbon. The productivity
of autotrophs, such as plants, is called primary productivity, while the
productivity of heterotrophs, such as animals, is called secondary productivity
Primary production is the synthesis of new organic material from inorganic
molecules such as H2O and CO2. It is dominated by the process of photosynthesis
which uses sunlight to synthesise organic molecules such as sugar
Secondary
production
is
the
generation
of biomass of heterotrophic (consumer) organisms in a system. This is driven by
the transfer of organic material between trophic levels, and represents the quantity
of new tissue created through the use of assimilated food. Secondary production is
sometimes defined to only include consumption of primary producers
39
by herbivorous consumers[2] (with
tertiary
production
referring
to carnivorous consumers),[3] but is more commonly defined to include all
biomass generation by heterotrophs.[1]
Organisms
responsible
for
secondary
production
include
animals, protists, fungi and many bacteria. Secondary production can be estimated
through a number of different methods including increment summation, removal
summation, the instantaneous growth method and the Allen curve method. [4] The
choice between these methods will depend on the assumptions of each and the
ecosystem under study. For instance, whether cohorts should be distinguished,
whether linear mortality can be assumed and whether population growth is
exponential.
The transfer of food energy from its source in autotrophs (plants) through a
series of organisms that consume and are consumed is termed the food chain. At
each transfer, a proportion (often as high as 80 or 90 percent) of the potential
energy is lost as heat. Therefore, the shorter the food chain—or the nearer the
organism to the producer trophic level—the greater the energy available to that
population. However, whereas the quantity of energy declines with each transfer,
the quality or concentration of the energy that is transferred increases.
Food chains are of two basic types:
(1) The grazing food chain, which, starting from a green plant base, goes to
grazing herbivores (organisms eating living plant cells or tissues) and on to
carnivores (animal eaters); and
(2) The detritus food chain, which goes from nonliving organic matter to microorganisms and then to detritus-feeding organisms (detritivores) and their
predators.
Food chains are not isolated sequences they are interconnected. The
interlocking pattern is often spoken of as the food web. In complex natural
communities, organisms whose nourishment is obtained from the Sun through the
same number of steps are said to belong to the same trophic level.
Thus, green plants occupy the first level (the producer trophic level), plant
eaters (herbivores) occupy the second level (the primary consumer trophic level),
40
primary carnivores occupy the third level (the secondary consumer trophic level),
and secondary carnivores occupy the fourth level (the tertiary consumer trophic
level). This trophic classification is one of function and not one of species as such.
A given species population may occupy one or more trophic levels according to
the source of the energy actually assimilated.
Transfer of Energy in Food Chains and Food Webs:
Food chains are vaguely familiar to everyone, as we eat the big fish
that ate the little fish that ate the zooplankton that ate the phytoplankton that
fixed the energy of the Sun; or we may eat the cow that ate the grass that fixed
the light energy of the Sun; or we may use a much shorter food chain by
directly eating the grain that fixed the energy of the Sun. In the last case,
human beings function as primary consumers at the second trophic level.
In the grass-cow-human food chain, we function at the third trophic
level, as secondary consumers. In general, humans tend to be both primary and
secondary consumers as our diet most often comprises a mixture of plant and
animal foods. Animals that consume both plant and animal matter are
frequently referred to as omnivores. Accordingly, the energy flow is divided
between two or more trophic levels in proportion to the percentage of plant
and animal food eaten.
Potential energy is lost at each food transfer. Only a small portion
(typically less than 1 percent) of the available solar energy is fixed by the plant
in the first place. Consequently, the number of consumers (such as people) that
can be supported by a given output of primary production very much depends
on the length of the food chain; each link in our traditional agricultural food
chain decreases the available energy by about one order of magnitude (about
tenfold).
Therefore, fewer people can be supported on a given amount of
primary production when large amounts of meat are part of the diet. However,
as emphasized in the statement, as the quantity goes down with each transfer,
the energy concentration (quality), goes up, a sort of “bad news-good news”
story.
41
Where the nutritional quality of the energy source is high, transfer
efficiencies can be much higher than 20 percent. However, because both
plants and animals produce a lot of hard-to-digest organic matter (cellulose,
lignin, and chitin) together with chemical inhibitors that discourage would-be
consumers, typical transfers between whole trophic levels average 20 percent
or less.
Energy quality is the contrast between different forms of energy, the
different trophic levels in ecological systems and the propensity of energy to
convert from one form to another. The concept refers to the empirical
experience of the characteristics, or qualia, of different energy forms as
they flow and
transform.
It
appeals
to
our
common perception of
the heat value, versatility, and environmental performance of different energy
forms and the way a small increment in energy flow can sometimes produce a
large transformation effect on both energy physical state and energy. For
example the transition from a solid state to liquid may only involve a very
small addition of energy. Methods of evaluating energy quality are sometimes
concerned
with
developing
a
system
of
ranking
energy
qualities
in hierarchical order.
Metabolism, the sum of the chemical reactions that take place within
each cell of a living organism and that provide energy for vital processes and
for synthesizing new organic material. Living organisms are unique in that
they can extract energy from their environments and use it to carry out
activities such as movement, growth and development, and reproduction. But
how do living organisms—or, their cells—extract energy from their
environments, and how do cells use this energy to synthesize and assemble the
components from which the cells are made?
The unity of life
At the cellular level of organization, the main chemical processes of all
living matter are similar, if not identical. This is true for animals, plants, fungi,
or bacteria; where variations occur (such as, for example, in the secretion
42
of antibodies by some molds), the variant processes are but variations on
common themes. Thus, all living matter is made up of large molecules
called proteins, which provide support and coordinated movement, as well as
storage and transport of small molecules, and, as catalysts, enable chemical
reactions to take place rapidly and specifically under mild temperature,
relatively low concentration, and neutral conditions (i.e., neither acidic nor
basic). Proteins are assembled from some 20 amino acids, and, just as the 26
letters of the alphabet can be assembled in specific ways to form words of
various lengths and meanings, so may tens or even hundreds of the 20 aminoacid “letters” be joined to form specific proteins. Moreover, those portions of
protein molecules involved in performing similar functions in different
organisms often comprise the same sequences of amino acids.
There is the same unity among cells of all types in the manner in which
living organisms preserve their individuality and transmit it to their offspring.
For example, hereditary information is encoded in a specific sequence of bases
that make up the DNA (deoxyribonucleic acid) molecule in the nucleus of
each
cell.
Only
four
bases
DNA: adenine, guanine, cytosine,
are
used
and thymine.
Just
in
synthesizing
as
the Morse
Code consists of three simple signals—a dash, a dot, and a space—the precise
arrangement of which suffices to convey coded messages, so the precise
arrangement of the bases in DNA contains and conveys the information for the
synthesis and assembly of cell components. Some primitive life-forms,
however, use RNA (ribonucleic acid; a nucleic acid differing from DNA in
containing
the sugar ribose instead
of
the
sugar deoxyribose and
the
base uracil instead of the base thymine) in place of DNA as a primary carrier
of genetic information. The replication of the genetic material in these
organisms must, however, pass through a DNA phase. With minor exceptions,
the genetic code used by all living organisms is the same.
The chemical reactions that take place in living cells are similar as
well. Green plants use the energy of sunlight to convert water (H2O)
and carbon dioxide (CO2) to carbohydrates (sugars and starches), other organic
43
(carbon-containing) compounds, and molecular oxygen (O2). The process
of photosynthesis requires energy, in the form of sunlight, to split one water
molecule into one-half of an oxygen molecule (O 2; the oxidizing agent) and
two hydrogen atoms (H; the reducing agent), each of which dissociates to
one hydrogen ion (H+) and one electron. Through a series of oxidationreduction reactions, electrons (denoted e−) are transferred from a donating
molecule (oxidation), in this case water, to an accepting molecule (reduction)
by a series of chemical reactions; this “reducing power” may be coupled
ultimately to the reduction of carbon dioxide to the level of carbohydrate. In
effect, carbon dioxide accepts and bonds with hydrogen, forming
carbohydrates (Cn[H2O]n).Living organisms that require oxygen reverse this
process: they consume carbohydrates and other organic materials, using
oxygen synthesized by plants to form water, carbon dioxide, and energy. The
process that removes hydrogen atoms (containing electrons) from the
carbohydrates and passes them to the oxygen is an energy-yielding series of
reactions.
In plants, all but two of the steps in the process that converts carbon
dioxide to carbohydrates are the same as those steps that synthesize sugars
from simpler starting materials in animals, fungi, and bacteria. Similarly, the
series of reactions that take a given starting material and synthesize certain
molecules that will be used in other synthetic pathways are similar, or
identical, among all cell types. From a metabolic point of view, the cellular
processes that take place in a lion are only marginally different from those that
take place in a dandelion.
The term "carrying capacity," long known to ecologists, has also
recently become popular. It "refers to the limit to the number of humans the
earth can support in the long term without damage to the environment."
(Giampietro, et. al. 1992) The troublesome phrase here is "without damage to
the environment." One damages the environment when one kills a mosquito,
builds a fire, erects a house, develops a subdivision, builds a power plant,
constructs a city, explodes a nuclear weapon, or wages nuclear war.
44
The concept of carrying capacity is central to discussions of population
growth. Since the publication of the original paper, the concept has been
examined by Cohen in a book How Many People can the Earth Support?
(Cohen 1995) Cohen makes a scholarly examination of many past estimates of
the carrying capacity of the Earth, and concludes that it is not possible to say
how many people the Earth can support. Furthermore, any calculated estimate
of the carrying capacity of the Earth may be challenged and will certainly be
ignored.
Many facts testify to this statement. It is estimated that somewhere
between 20 and 40 percent of the earth's primary productivity, from plant
photosynthesis on land and in the sea, is now appropriated for human use. An
impact on the global environment of this magnitude is properly the cause for
alarm.We note that growing populations require growing numbers of jobs and
growing rates of consumption of resources, and the satisfaction of these
requirements is almost always at the expense of the carrying capacity of the
environment. The inevitable and unavoidable conclusion is that if we want to
stop the increasing damage to the global environment, as a minimum, we must
stop population growth.It won't be easy. Jerome B. Wiesner was President of
M.I.T. (1971-1980) and was Special Assistant for Science and Technology for
Presidents Kennedy and Johnson. He made a very sobering observation about
the conflict between the needs of humans and the needs of the environment if
we are to maintain the carrying capacity of the Earth. (Wiesner 1989)There are
no clear-cut ways to reconcile economic growth with the measures needed to
curb environmental degradation, stretch dwindling natural resources and solve
health and economic problems.
The source and quality of available energy determine to a greater or
lesser degree the kinds and numbers of organisms, the pattern of functional
and developmental processes, and, directly or indirectly, the lifestyle of human
beings. As energy is the common denominator and the ultimate forcing
function of all ecosystems, whether natural or designed by humans, it provides
a logical basis for a “first-order” classification.
45
On this basis, it is convenient to distinguish four classes of ecosystems:
1. Natural, unsubsidized solar-powered ecosystems.
2. Natural solar-powered ecosystems subsidized by other natural energies.
3. Human-subsidized solar-powered ecosystems.
4. Fuel-powered, urban-industrial techno-ecosystems (using energy from fossil
fuels or other organic or nuclear fuels).
This classification is based on the input environment, and it contrasts
with and complements the biome classification, which is based mainly on the
major vegetative structure of the ecosystem.
Ecosystems rely on two dissimilar sources of energy:
(1) The Sun and
(2) Chemical or Nuclear Fuels.
There are several different factors that control the primary productivity
of energy and biomass flow. Energy flow is the amount of energy that moves
through a food chain. The energy input, or energy that enters the ecosystem, is
measured in Joules or calories. Accordingly, the energy flow is also called
calorific flow. In the study of energy flow, ecologists try to quantify the
importance of different species and feeding relationships.
The largest source of energy for an ecosystem is the sun. Energy that is
not used in an ecosystem is eventually lost as heat. Energy and nutrients are
passed around through the food chain, when one organism eats another
organism. Any energy remaining in a dead organism is consumed by
decomposers. Nutrients can be cycled through an ecosystem but energy is
simply lost over time.
An example of energy flow in an ecosystem would begin with the
autotrophs that take energy from the sun. Herbivores then feed on the
autotrophs and change the energy from the plant into energy that they can use.
Carnivores subsequently feed on the herbivores and, finally, other carnivores
prey on the carnivores.
46
In each case, energy is passed on from one trophic level to the next
trophic level and each time some energy is lost as heat into the environment.
This is due to the fact that each organism must use some energy that they
received from other organisms in order to survive. The top consumer of a food
chain will be the organism that receives the least amount of energy.
Hairston and Hairston (1993)^ , believe that there is a cause and effect
relationship that results in any given trophic structure. Specifically, they state
that it is trophic structure, rather than energetics that controls the amount of
energy consumed at each trophic level and that "ecological efficiencies" are
the product of a trophic structure, not a determining factor. Further, they state
that trophic structure is instead the result of competition and predator-prey
interactions. It is important to remember that many species may occupy each
trophic level and are so subject to interspecific competition. This is especially
true for producers, carnivores, and decomposers (Hairston, Smith, and
Slobodkin, 1960).
47
Utilization of Learning
Answer the following;
1.
2.
3.
4.
5.
6.
7.
8.
9.
explain the fundamental concepts of energy;
explain Solar Radiation and the Energy Environment;
discuss the concept of productivity;
explain energy partitioning in Food Chains and Food Webs;
explain energy quality;
discuss metabolism and Size of individuals;
discuss the concepts of carrying capacity and sustainability;
illustrate the energy-based classification of ecosystems;
discuss energy futures
Supplementary:
Essentials of Ecology eBooks (Available in Google Classroom)
https://www.energy.gov
https://www.britannica.com
https://www.albartlett.org
Human activities have already caused great change in the global environment.
May observes that (May 1993):
https://www.youtube.com/watch?v=BHn-SQu5450
48
Lesson 2: Basic Types of Biogeochemical Cycles
Target Outcomes
At the end of the lesson, you are expected to:
1. Explain the basic types of Biogeochemical Cycles
2.
illustrate Nitrogen Cycle
3.
illustrate Phosphorus Cycle
4. illustrate Sulfur Cycle
5. illustrate Carbon Cycle
6. illustrate Hydrologic Cycle
7.
discuss turnover and Residence Times
8. discuss watershed biogeochemistry
9.
illustrate Nonessential Elements Cycle
10. illustrate Nutrient Cycling in the Tropics
11. explain recycling pathways: The Cycling lndex
12. discuss Global Climate Change
Abstraction
Basic types of Biogeochemical Cycles
Nutrients ultimately are chemical compounds. So, there is this natural
pathway where the living matter is constantly circulated. Nutrients are never
lost from an ecosystem. Recycling of these nutrients happens at every stage.
This recycling of the nutrients through different components in an ecosystem is
called the nutrient cycle or biogeochemical cycle.
Here, the chemical elements are always recycled, whereas heat is
dissipated. Energy flows but the matter is always recycled. To get a better idea,
49
see the movement of water, which is a chemical compound (H2O). It moves
between different living and non-living forms in various places in the
biosphere.
50
Types of Biogeochemical cycles
Broadly, the biogeochemical cycles can be divided into two types, the
gaseous biogeochemical cycle and sedimentary biogeochemical cycle based on
the reservoir. Each reservoir in a nutrient cycle consists of an abiotic portion
and an exchange pool, where there is a rapid exchange that occurs between
the biotic and abiotic aspects.
The gaseous
cycles exist
in
the atmosphere
(air) or
Oceans
through evaporation. The different gaseous cycles are the nitrogen cycle,
carbon cycle, oxygen cycle, and the water cycle.
The sedimentary cycles have the earth’s crust as the reservoir pool.
These cycles include the chemical components that are more earthbound, such
as iron, calcium, sulphur etc. The gaseous cycles move more rapidly when
compared to the sedimentary cycles. One of the primary reasons for this could
be the large atmospheric reservoir.
Nitrogen Cycle
Nitrogen is a very important element that is present in the genetic
material – DNA and RNA. The nitrogen cycle is considered as the most
complex of all biogeochemical cycles and it exists in nature in many forms.
Nitrification, Denitrification, Nitrogen fixation etc. are all processes that are
associated with the nitrogen cycle. In conclusion, all these different
biogeochemical cycles do not occur in isolation. The most important
connecting link is the movement of water through the water cycle. The
movement of water is very important for the discharge of phosphate and
nitrogen into the various water bodies, including the oceans. The ocean is a
major reservoir that holds carbon, another important element in the
biogeochemical cycles.
Phosphorus Cycle
51
The phosphorus cycle is the biogeochemical cycle that describes the
movement of phosphorus through the lithosphere, hydrosphere, and biosphere.
Unlike many other biogeochemical cycles, the atmosphere does not play a
significant role in the movement of phosphorus, because phosphorus and
phosphorus-based compounds are usually solids at the typical ranges of
temperature and pressure found on Earth. The production of phosphine gas
occurs in only specialized, local conditions. Therefore, the phosphorus cycle
should be viewed from whole Earth system and then specifically focused on
the cycle in terrestrial and aquatic systems.
On the land, phosphorus gradually becomes less available to plants
over thousands of years, since it is slowly lost in runoff. Low concentration of
phosphorus in soils reduces plant growth, and slows soil microbial growth - as
shown in studies of soil microbial biomass. Soil microorganisms act as both
sinks and sources of available phosphorus in the biogeochemical
cycle. Locally, transformations of phosphorus are chemical, biological and
microbiological: the major long-term transfers in the global cycle, however,
are driven by tectonic movements in geologic time.Humans have caused major
changes to the global phosphorus cycle through shipping of phosphorus
minerals, and use of phosphorus fertilizer, and also the shipping of food from
farms to cities, where it is lost as effluent.
Sulfur Cycle
The sulfur cycle is the collection of processes by which sulfur moves
between rocks, waterways and living systems. Such biogeochemical cycles are
important in geology because they affect many minerals. Biochemical cycles
are also important for life because sulfur is an essential element, being a
constituent of many proteins and cofactors, and sulfur compounds can be used
as oxidants or reductants in microbial respiration.[1] The global sulfur cycle
involves the transformations of sulfur species through different oxidation
states, which play an important role in both geological and biological
processes.
Carbon Cycle
52
Any matter is called organic if it has carbon in it. Carbon is essential
and is required to produce the molecules of nutrients such as carbohydrates,
proteins, and fats. Plants use carbon dioxide and prepare food. Animals, in turn,
consume plants. When plants and animals decompose, they release carbon
dioxide.Animals also release carbon dioxide during their respiration process.
Carbon is also released when organic matter in burnt. In this way, carbon
dioxide finds its way back to the atmosphere. This is again taken up by plants
and the biogeochemical cycle continues.
Hydrologic Cycle
The hydrologic cycle begins with the evaporation of water from the
surface of the ocean. As moist air is lifted, it cools and water
vapor condenses to form clouds. Moisture is transported around the globe until
it returns to the surface as precipitation. Once the water reaches the ground,
one of two processes may occur; 1) some of the water may evaporate back into
the atmosphere or 2) the water may penetrate the surface and
become groundwater. Groundwater either seeps its way to into the oceans,
rivers,
and
streams,
or
is
released
back
into
the
atmosphere
through transpiration. The balance of water that remains on the earth's surface
is runoff, which empties into lakes, rivers and streams and is carried back to
the oceans, where the cycle begins again.Lake effect snowfall is good example
of the hydrologic cycle at work. Below is a vertical cross-section summarizing
the processes of the hydrologic cycle that contribute to the production of lake
effect snow. The cycle begins as cold winds (horizontal blue arrows) blow
across a large lake, a phenomena that occurs frequently in the late fall and
winter months around the Great Lakes.
Turnover and Residence Times
Turnover time is defined as the ratio of the quantity of a material or
energy in a system to its outflow rate. It may also be viewed as the inverse of
the fraction of material or energy that leaves per unit time. For a system in
equilibrium, the outflow rate is equivalent to the flow-through rate and the
turnover time of a substance is equal to the residence time, that is, the mean
53
transit time between entry into and exit from the system. Turnover time
provides a timescale for the replacement of energy or materials in a system
and is a useful tool for analysis of material and energy fluxes, pool sizes, and
the time required for pools to attain steady state after a change in loading
rate.The concept of turnover is also applicable to analysis of species
appearance and extinction rates in local systems, and to analysis of harvested
populations such as in marine fisheries.
The residence time of a fluid parcel is the total time that the parcel has
spent inside a control volume (e.g.: a chemical reactor, a lake, a human body).
The residence time of a set of parcels is quantified in terms of the frequency
distribution of the residence time in the set, which is known as residence time
distribution (RTD), or in terms of its average, known as mean residence time.
Residence time plays an important role in chemistry and especially
in environmental
science and pharmacology.
Under
the
name lead
time or waiting time it plays a central role respectively in supply chain
management and queueing theory, where the material that flows is usually
discrete instead of continuous.
The concept of residence time originated in models of chemical
reactors. The first such model was an axial dispersion model by Irving
Langmuir in 1908. This received little attention for 45 years; other models
were developed such as the plug flow reactor model and the continuous
stirred-tank reactor, and the concept of a washout function (representing the
response to a sudden change in the input) was introduced. Then, in 1953, Peter
Danckwerts resurrected the axial dispersion model and formulated the modern
concept of residence time.
Watershed biogeochemistry
Watershed Ecology and Biogeochemistry’ addresses the foundational
concepts and modern challenges within the broad field of watershed science.
Here we will take an integrative approach that focuses on the hydrological,
biogeochemical and ecological connections between upland, riparian, and
aquatic components of forest landscapes. Specific topics includes: 1) an
54
overview of catchment hydrology and water balance, 2) elemental transport
and processing along hill slopes and riparian zones, 3) controls over material
exchange at the land-water interface, 4) biogeochemical cycling in streams
and rivers, 5) the biogeochemical significance of wetlands and lakes within
catchments, and 6) the interface between forest management and watershed
science in boreal lands. General themes in watershed science will be explored
through discussions of literature that will be coordinated with short lectures.
More specific questions and methodological approaches will be introduced
using a series of excursions and activities within the Krycklan catchment.
Nonessential Elements Cycle
Although nonessential elements may have little or no known value to
an organism or species, they often pass back and forth between organisms and
their environment in the same general manner as do the essential elements.
Many of these nonessential elements are involved in the general sedimentary
cycle, and some find their way into the atmosphere. Many nonessential
elements become concentrated in certain tissues, sometimes because of their
chemical similarity to specific vital elements.
Chiefly because human activities involve many of the nonessential
elements, ecologists have become concerned with the cycling of these
elements; indeed, all of us must be concerned with the increasing volume of
toxic wastes that are discharged or that inadvertently escape into the
environment and contaminate the basic cycles of vital elements.
Many marine animals concentrate elements—such as arsenic, a
phosphorus analog—that they cannot remove from their environment. They
then convert the arsenic into an inert chemical form stored in their tissues.
Some elements, such as mercury, are passed up the food chain; thus, large
predatory animals tend to accumulate high concentrations of it.
This process, termed biological magnification, is the reason why a
number of fishes, such as swordfish and tuna, contain potentially harmful
amounts of mercury. Most nonessential elements have little effect at the
concentrations normally found in most natural ecosystems, probably because
organisms have become adapted to their presence.
55
Therefore, their biogeochemical movement would be of little interest,
were it not for the byproducts of the mining, manufacturing, chemical, and
agricultural industries that contain high concentrations of heavy metals, toxic
organic compounds, and other potentially dangerous materials that all too
often find their way into the environment.
Nutrient Cycling in the Tropics
The majority of nutrients in the tropical rainforest are stored in
the biomass. The biomass is all the living things in an ecosystem,
including plants and animals. Nutrients are rapidly recycled in the
tropical rainforest biome. The warm, moist climate provides ideal
conditions for decomposers to break down organic material in the
litter layer very quickly. The litter layer is all the dead organic
material such as fallen leaves, dead wood or dead animals on the
surface of the soil. Vegetation takes up nutrients which are dissolved
in the soil.
The soil is formed by the mixing of dead organic material with
weathered bedrock. Soils in the rainforest are mainly thin and poor.
Nutrient levels in the soil are low due to the leaching (washing away
of nutrients) by the heavy equatorial rain. This leaching means that
the lower layers of the soils lack the nutrients and minerals needed by
the lush vegetation. Also, rainforest vegetation rapidly absorbs
nutrients from the soil. Soils are often red in colour as they are rich in
iron.
56
The nutrient cycle in the rainforest is an excellent example of
interdependence. the diagram above shows the links between
different stores of nutrients in the rainforest. Decomposers rely on
fallen leaves, branches and dead animals to thrive. In turn, nutrients
from decomposed matter enter the soil providing nutrients to support
the growth of vegetation that is consumed by primary consumers.
The nutrient cycle in the rainforest is very fragile. If a nutrient
flow changes this can have a negative impact on the ecosystem. For
example, when deforestation occurs the litter layer no longer receives
organic matter and the soil quickly becomes infertile. Because there is
no vegetation cover to protect the soil nutrients are rapidly leached by
heavy equatorial rainfall.
57
Recycling pathways: The Cycling lndex
It is instructive to review the subject of biogeochemistry in terms of
recycling pathways, because the recycling of water and nutrients is a vital
process in ecosystems and is increasingly becoming an important concern for
humankind.
Five major recycling pathways can be distinguished:
(1) By microbial decomposition;
(2) By animal excretions;
(3) By direct recycling from plant to plant through microbial symbioses;
(4) By physical means involving direct action of solar energy; and
(5) By use of fuel energy, as in the industrial fixation of nitrogen.
Recycling requires dissipation of energy from some source such as
organic matter, solar radiation, or fossil fuel. The relative amount of recycling
in different ecosystems can be compared by calculating a cycling index based
on the ratio of the sum of the amounts cycling between compartments within
the system to total through-flow.
It is appropriate to focus on the cycling of nutrients in the biologically
active portion of the ecosystem. The total energy environment was considered
first, and then attention was focused on the fate of that small energy fraction
involved in the food chain. Also, a discussion of biological regeneration is
relevant because recycling has increasingly become a major goal for human
societies.
Global Climate Change
Climate change includes both the global warming driven by human
emissions of greenhouse gases, and the resulting large-scale shifts in weather
patterns.[1] Though there have been previous periods of climatic change, since
the mid-20th century the amount of change and the rate of change have been
unprecedented. That human activity has caused climate change is not disputed
by any scientific body of national or international standing.[5] The largest
58
driver has been the emission of greenhouse gases. Over 90% of these
emissions
are carbon
dioxide (CO
2) and methane, with fossil-fuel burning being the main source, and secondary
contributions
from agricultural and deforestation.
Temperature
rise
is
accelerated or tempered by climate feedbacks, such as loss of sunlightreflecting snow and ice cover, increased water vapour (a greenhouse gas
itself), and changes to land and ocean carbon sinks.
Because land surfaces heat faster than ocean surfaces, deserts are
expanding
and heat
waves and wildfires are
common.[6] Surface
more
temperature rise is greatest in the Arctic, where it has contributed to
melting permafrost, and the retreat of glaciers and sea ice. Increasing
atmospheric
energy
and
rates
of
evaporation
cause more
intense
storms and weather extremes, which damage infrastructure and agriculture.
[7]
Rising temperatures are limiting ocean productivity and harming fish stocks
in most parts of the globe. Current and anticipated effects from under
nutrition, heat stress and disease have led the World Health Organization to
declare climate change the greatest threat to global health in the 21st century.
Environmental effects include the extinction or relocation of many species as
their ecosystems change, most immediately in coral reefs, mountains, and
the Arctic. Even if efforts to minimize future warming are successful, some
effects will continue for centuries, including rising sea levels, rising ocean
temperatures, and ocean acidification from elevated levels of CO2.
Intergovernmental Panel on Climate Change (IPCC) assesses the
scientific, technical and socioeconomic information relevant to understanding
of human-induced climate change. The IPCC has assessed that there is much
greater risk to human and natural systems if warming exceeds pre-industrial
levels by 1.5 °C (2.7 °F).[9] Under the Paris Agreement, nations are
making climate pledges to reduce greenhouse gas emissions. Even if nations
follow through on current promises, global warming can still reach about
2.8 °C (5.0 °F) by 2100.[10] Reducing emissions of methane to near-zero levels
and CO
2 to
net-zero
by
2050
would
limit
warming
to
1.5 °C
(2.7 °F).
Mitigation efforts include the development and deployment of low-carbon
59
energy technologies, enhanced energy efficiency, policies to reduce fossil fuel
emissions, reforestation,
and forest
preservation.
Controversial climate-
engineering technologies have been proposed if mitigation fails. Societies and
governments are working to adapt to current and future global-warming
effects through improved coastline protection, better disaster management, and
the development of more resistant crops.
Utilization of Learning
1. Illustrate the following;
a. illustrate Nitrogen Cycle
b.
illustrate Phosphorus Cycle
c. illustrate Sulfur Cycle
d. illustrate Carbon Cycle
e. illustrate Hydrologic Cycle
f. Nonessential Elements Cycle
g. Nutrient Cycling in the Tropics
2. What are the basic types of Biogeochemical Cycles
3. What is watershed biogeochemistry?
4. What is a turnover and residence time?
5. What is a recycling pathway?
6. What is global climate change?
Supplementary Materials
Essentials of Ecology eBooks (Available in Google Classroom)
https://www.internetgeography.net
https://en.wikipedia.org/
Chapter 3: Limiting and Regulatory Factors and Population Ecology
60
Lesson 1: Concept of Limiting Factors
Target Outcomes
At the end of the lesson, you are expected to:
1. discuss the concept of limiting factors;
2. understand the factor compensation and ecotypes;
3. discuss the conditions of existence as regulatory factors;
4. explain the organizing component of terrestrial ecosystems;
5. explain Fire Ecology;
6. explain the other physical limiting factors;
7. understand the biological magnification of toxic substances; and
8. understand anthropogenic stress as a limiting factor for industrial Society.
Abstraction
The concept of limiting factors
A limiting factor is a variable of a system that causes a noticeable
change in output or another measure of a type of system. The limiting factor is
in a pyramid shape of organisms going up from the producers to consumers
and so on. A factor not limiting over a certain domain of starting conditions
may yet be limiting over another domain of starting conditions, including that
of the factor.
The identification of a factor as limiting is possible only in distinction
to one or more other factors that are non-limiting. Disciplines differ in their
use of the term as to whether they allow the simultaneous existence of more
than one limiting factor which (may then be called "co-limiting"), but they all
require the existence of at least one non-limiting factor when the terms are
used. There are several different possible scenarios of limitation when more
61
than one factor is present. The first scenario, called single limitation occurs
when only one factor, the one with maximum demand, limits the
System. Serial co-limitation is when one factor has no direct limiting effects
on the system, but must be present to increase the limitation of a second factor.
A third scenario, independent limitation, occurs when two factors both have
limiting effects on the system but work through different mechanisms.
Another scenario, synergistic limitation, occurs when both factors contribute
to the same limitation mechanism, but in different ways.
In 1905 Frederick Blackman articulated the role of limiting factors as
follows: "When a process is conditioned as to its rapidity by several separate
factors the rate of the process is limited by the pace of the slowest factor." In
terms of the magnitude of a function, he wrote, "When the magnitude of a
function is limited by one of a set of possible factors, increase of that factor,
and of that one alone, will be found to bring about an increase of the
magnitude of the function."
The factor compensation and ecotypes
Organisms are not subjugated to the physical environment; they adapt
themselves and modify the physical environment to reduce the limiting effects
of temperature, light, water, and other physical conditions of existence. Such
factor compensation is particularly effective at the community level of
organization, but it also occurs within species.
Species with wide geographical ranges almost always develop locally
adapted populations called ecotypes that have optima and limits of tolerance
adjusted to local conditions. Ecotypes are genetically differentiated subspecies
that are well adapted to a particular set of environmental conditions.
Compensation along gradients of temperature, light, pH, or other factors
usually involves genetic changes of ecotypes, but it can occur by physiological
adjustments without genetic fixation.
Species that range widely along a gradient of temperature or other
conditions often differ physiologically and sometimes morphologically in
different parts of their range. Usually, genetic changes are involved, but factor
compensation can be accomplished without genetic fixation by physiological
62
adjustments in organ functions or by shifts in enzyme-substrate relationships
at the cellular level.
Reciprocal transplants provide a convenient method of determining to
what extent genetic fixation is involved in ecotypes. McMillan (1956), for
example, found that prairie grasses of the same species (and to all appearances
identical) transplanted into experimental gardens from different parts of their
range responded quite differently to light.
In each case, the timing of growth and reproduction was adapted to the
area from which the grasses were transplanted. The importance of genetic
fixation in local strains has often been overlooked in applied ecology;
restocking or transplanting of plants and animals frequently fail because
individuals from remote regions are used instead of locally adapted stock.
Transplanting also frequently disrupts local species interactions and regulatory
mechanisms.
The conditions of existence as regulatory factors
In population ecology, a regulating factor, also known as a limiting
factor, it is something that keeps a population at equilibrium (neither
increasing nor decreasing in size over time).An example of a regulating factor
would be predation or food supply. If the population increases to a certain
size, there will be less food for each organism. This will lead to fewer births (a
decrease in fecundity) and more deaths, meaning the growth rate will decrease
to zero. Therefore, food is a regulating factor in this scenario, as food supply
keeps the population at relative equilibrium. Populations in predator-prey
relationships are similarly limited by the populations of each other.
The organizing component of terrestrial ecosystems
A terrestrial
ecosystem is a type of ecosystem found only on
landforms. Six primary terrestrial ecosystems exist: tundra, taiga, temperate
deciduous forest, tropical rain forest, grassland, deserts.
A community of organisms and their environment that occurs on the
land masses of continents and islands, terrestrial ecosystems are distinguished
63
from aquatic ecosystems by the lower availability of water and the consequent
importance of water as a limiting factor. Terrestrial ecosystems are
characterized by greater temperature fluctuations on both a diurnal and
seasonal basis that occur in aquatic ecosystems in similar climates.
Terrestrial ecosystems occupy 55,660,000 mi2 (144,150,000 km2), or
28.26% of Earth's surface. Although they are comparatively recent in the
history of life (the first terrestrial organisms appeared in the Alchi period,
about 425 million years ago) and occupy a much smaller portion of Earth's
surface than marine ecosystems, terrestrial ecosystems have been a major site
of adaptive radiation of both plants and animals. Major plant taxa in terrestrial
ecosystems are members of the division Magnoliophyta (flowering plants), of
which there are about 275,000 species, and the division Pinophyta (conifers),
of
which
there
are
about
500
species.
Members
of
the
division Bryophyta (mosses and liverworts), of which there are about 24,000
species, are also important in some terrestrial ecosystems. Major animal taxa
in terrestrial ecosystems include the classes Insecta (insects) with about
900,000 species, Aves (birds) with 8,500 species, and Mammalia (mammals)
with approximately 4,100 species.
Organisms in terrestrial ecosystems have adaptations that allow them
to obtain water when the entire body is no longer bathed in that fluid, means of
transporting the water from limited sites of acquisition to the rest of the body,
and means of preventing the evaporation of water from body surfaces. They
also have traits that provide body support in the atmosphere, a much
less buoyant medium than water, and other traits that render them capable of
withstanding the extremes of temperature, wind, and humidity that
characterize terrestrial ecosystems. Finally, the organisms in terrestrial
ecosystems have evolved many methods of transporting gametes in
environments where fluid flow is much less effective as a transport medium.
The organisms in terrestrial ecosystems are integrated into a functional
unit by specific, dynamic relationships due to the coupled processes of energy
and chemical flow. Those relationships can be summarized by schematic
diagrams of trophic webs, which place organisms according to their feeding
relationships. The base of the food web is occupied by green plants, which are
64
the only organisms capable of utilizing the energy of the Sun and inorganic
nutrients obtained from the soil to produce organic molecules. Terrestrial food
webs can be broken into two segments based on the status of the plant material
that enters them. Grazing food webs are associated with the consumption of
living plant material by herbivores. Detritus food webs are associated with the
consumption of dead plant material by detritivores. The relative importance of
those two types of food webs varies considerably in different types of
terrestrial ecosystems. Grazing food webs are more important in grasslands,
where over half of the net primary productivity may be consumed by
herbivores. Detritus food webs are more important in forests, where less than
5% of net primary productivity may be consumed by herbivores.
Fire Ecology
Fire ecology is a scientific discipline concerned with natural processes
involving fire in an ecosystem and the ecological effects, the interactions
between fire and the abiotic and biotic components of an ecosystem, and the
role
as
an
ecosystem
process.
Many
ecosystems,
particularly prairie, savanna, chaparral and coniferous forests, have evolved
with fire as an essential contributor to habitat vitality and renewal.[1] Many
plant species in fire-affected environments require fire to germinate, establish,
or to reproduce. Wildfire suppression not only eliminates these species, but
also the animals that depend upon them.[2]
Campaigns in the United States have historically molded public
opinion to believe that wildfires are always harmful to nature. This view is
based on the outdated beliefs that ecosystems progress toward an equilibrium
and that any disturbance, such as fire, disrupts the harmony of nature. More
recent ecological research has shown, however, that fire is an integral
component in the function and biodiversity of many natural habitats, and that
the organisms within these communities have adapted to withstand, and even
to exploit, natural wildfire. More generally, fire is now regarded as a 'natural
disturbance', similar to flooding, wind-storms, and landslides, that has driven
the evolution of species and controls the characteristics of ecosystems.
65
Fire
suppression,
in
combination
with
other
human-caused
environmental changes, may have resulted in unforeseen consequences for
natural ecosystems. Some large wildfires in the United States have been
blamed on years of fire suppression and the continuing expansion of people
into
fire-adapted
ecosystems,
but climate
change is
more
likely
responsible. Land managers are faced with tough questions regarding how to
restore a natural fire regime, but allowing wildfires to burn is the least
expensive and likely most effective method.
The other physical limiting factors
A limiting factor is a resource or environmental condition which limits
the growth, distribution or abundance of an organism or population within
an ecosystem. These can be either physical or biological factors which can be
identified through a response of increased or decreased growth, abundance, or
distribution of a population, when the factor is changed and when the other
factors necessary to life are not. Limiting factors are theorized under Liebig’s
Law of the Minimum, which states that “growth is not controlled by the total
amount of resources available, but by the scarcest resource”. A limiting factor
restricts organisms from occupying their fundamental niche and results instead
in the fulfillment of their actual or realized niche.
Types of Limiting Factor
Density Dependent Factors
Density dependent factors are those factors whose effect on a
population is determined by the total size of the population. Predation and
disease, as well as resource availability, are all examples of density dependent
factors. As an example, disease is likely to spread quicker through a larger,
denser population, impacting the number of individuals within the population
more than it would in a smaller, more widely dispersed population.
Density Independent Factors
66
A density independent limiting factor is one which limits the size of a
population, but whose effect is not dependent on the size of the population (the
number of individuals). Examples of density independent factors include
environmentally stressful events such as earthquakes, tsunamis, and volcanic
eruptions, as well as sudden climate changes such as drought or flood, and
destructive occurrences, such as the input of extreme environmental
pollutants. Density independent factors will usually kill all members of a
population, regardless of the population size.
Physical and Biological Limiting Factors
Limiting factors can also be split into further categories. Physical
factors or abiotic factors include temperature, water availability, oxygen,
salinity, light, food and nutrients; biological factors or biotic factors, involve
interactions
between
organisms
such
as predation, competition, parasitism and herbivory.
The biological magnification of toxic substances
Biological magnification refers to the process where toxic substances
move up the food chain and become more concentrated at each level. These
substances are often pollutants from industries or pesticides from farming. An
example of biological magnification and its dangers is any small fish that
eats plankton that has been tainted with mercury. Hundreds of small fish might
then contain just few parts of the mercury, not enough to cause major harm.
On the image, the amount of mercury is measured in ppm, which means “parts
per million.” A bird then might eat hundreds of the small fish, so that now
instead of 200 ppm in a single fish, that bird has much higher levels of
mercury. The toxin amplifies as it moves up the food chain. Biological
magnification caused a crisis with eagles, where DDT was used to control
mosquitoes and other pests. Birds would accumulate toxic levels of DDT in
their bodies which would cause their eggs to become fragile and break. The
67
eagle almost became extinct, but lawmakers banned DDT and the eagle is now
in recovery.
Anthropogenic stress as a limiting factor for industrial society
Natural ecosystems exhibit considerable resistance, resilience, or both
to periodic severe or acute disturbance, probably because through evolutionary
time they have naturally adapted to it. Many organisms, in fact, require
stochastic (random) or periodic disturbances, such as fire or storms, for longterm persistence. Accordingly, ecosystems may recover rather well from many
periodic anthropogenic disturbances, such as harvest removal.
Chronic (persistent or continued) disturbance, however, may have
pronounced and prolonged effects, especially in the case of industrial
chemicals that are new to the environment. In such cases, organisms have no
evolutionary history of adaptation. Unless the increasing volume of highly
toxic wastes, which are the current by-product of high-energy, industrialized
societies, is reduced and ultimately eliminated at the source, toxic wastes will
increasingly threaten both human and ecosystem health and be a major
limiting factor for humankind.
Although any classification is somewhat arbitrary, it may be
instructive to consider anthropogenic stress on ecosystems under two
categories:
(1) Acute stress, characterized by sudden onset, sharp rise in intensity, and
short duration; and
(2) Chronic stress, involving long duration or frequent recurrence but
not high intensity—a “constantly vexing” disturbance. Natural ecosystems
exhibit considerable ability to deal with or recover from acute stress.
An example of acute stress is acute dose of municipal sludge input into
a stream ecosystem resulted in a fish kill, because bacterial decomposition
caused the stream’s oxygen content to approach zero. Once the sewage
treatment plant whose breakdown had caused the acute stress was repaired, the
stream initiated its recovery process. Another example of recovery following
acute stress is the buried seed strategy, a quick recovery mechanism that
facilitates forest regrowth after clear-cutting.
68
The effects of chronic stress are more difficult to assess, because
responses will not be so dramatic. It may be years before the full effects are
known, just as it took many years to understand the link between cancer and
smoking or the relationship between cancer and chronic low-level ionizing
radiation. Environmental “cancer” (disorderly growth of exotic species at
population or community levels) appears to provide an analogous situation
regarding ecological systems.
Of special concern to human health are industrial wastes containing
potential stressors that are new chemical creations and, hence, are
environmental factors to which living organisms and ecosystems have not had
a period of evolutionary history for adaptation or accommodation. Chronic
exposure to such anthropogenic factors can be expected to result in basic
changes in the structure and function of biotic communities, as acclimation
and genetic adaptation occur. During the transition or adaptation period,
organisms may be especially vulnerable to secondary factors, such as disease,
that can have catastrophic results. The increasing volume of toxic waste that
affects human health—either because of direct contact or through
contamination of food and drinking water—is approaching crisis proportions.
69
Utilization of Learning
Answer the following questions;
1. What is the concept of limiting factors?
2. What are the factors of compensation and ecotypes?
3. What are the conditions of existence as regulatory factors?
4. What are the organizing components of terrestrial ecosystems?
5. What is Fire Ecology?
6. List down the other physical limiting factors.
7. What are the biological magnifications of toxic substances?
8. Why anthropogenic stress is a limiting factor for industrial society?
Supplementary Materials
Essentials of Ecology eBooks (Available in Google Classroom)
http://www.ecologyessays.com
https://en.wikipedia.org
https://biologydictionary.net
70
Lesson 2: Population Ecology
Target Outcomes
At the end of the lesson, you are expected to:
1. understand the properties of the population;
2. explain the basic concepts of rate;
3. explain intrinsic Rate of Natural increase; and
4. understand the concept of carrying capacity.
Abstraction
The properties of the population
The central question in population ecology is: what determines structure and
functioning of populations and their variation in time and space? The aim of this
course is to acquire the appropriate tools to deal with this question in any real-life
situation through scientific research.
The term population, like all ecological entities, requires definition. This has
two purposes: a) to differentiate populations from other entities that are not
populations, and b) to differentiate between different populations. The most widely
accepted definition is that a population is a collection of individuals of the same
species occurring together in a particular space and time. Since populations consist of
individuals, which occur in communities together with other organisms, populations
should be examined at a different organizational level than both individual organisms
71
and communities. This is a matter of "focus" of observation: only overall quantities of
the collection of individuals and the interactions among the individuals are
considered. From the point of view of the population, whatever occurs within
individuals is "detail" and interactions with other organisms are part of the
"background". Both are essential for understanding populations, but describe
phenomena that can be examined by using a different focus.
The second purpose of the definition is more problematical. This is due to a high
degree
of
fuzziness
of
all
components
of
the
definition: individual, species, space and time. This is a problem inherent in biological
systems and reflects their diverse and dynamic character. The solution is to know the
target organisms well and to use ad hoc definitions that fit the specific question and
the unique properties of the organisms.
Problems often arise when defining where in space a population is. For some
organisms that are fixed to a certain place or move only short distances, we can know
exactly where the individuals are, but not where the boundaries of the population are.
In these cases decisions are often taken arbitrarily based on sampling considerations,
or based on landscape boundaries (a recognizable patch, a woodlot, etc.). On the other
hand, a population of animals migrating in flocks or herds, for instance, has clearly
recognizable boundaries at any moment, but its place changes constantly.
The most variable term in the definition is the individual, even though it is the
most tangible entity in ecology. In unitary organisms (most animals) there is usually
no problem recognizing individuals, because they are both genetically and
physiologically separate. Many species of plants and invertebrates, however, have
vegetative propagation to produce new individuals, besides sexual reproduction. In
such modular organisms new functional modules are formed (ramets) from a single
genetically unique individual (the genet). If the ramets are physiologically
independent, they can be counted as individuals, though not genetically distinct. This
is just like internodes and branches of a plant, except that the connections between
them are gone.
The term species may also pose problems, if taxonomic definitions of species
vary (splitting one species or lumping two species), or if the biological species
72
concept, requiring the possibility of mating between all individuals, is not applicable.
This is the case when there is no sexual reproduction at all, only fragmentation (a
form of vegetative propagation common in flatworms, for instance), or cleistogamy
(sexual reproduction by self-pollination without crossing between individuals in many
plants - wild barley, for instance).
2. Properties of populations
The question "What determines structure and functioning of a population?"
implies that we are interested in understanding which factors influence a population,
and how it responds to these factors. In order to deal with these questions, we have to
specify what properties populations have that can be described, and what kind of
factors can influence them. There are many differences between populations - first of
all between populations of different species, and even two populations of the same
species can be very different. Nevertheless, there are properties that all populations
possess, though in different shapes and proportions. These properties are:
a) dimensions - population density, abundance or size, based on the number of
individuals (per unit area, or in the entire population);
b) composition - the proportions of individuals with different states (gender, age,
developmental stage, or size);
c) dynamics - changes in time of the dimensions and composition of a population; this
includes the rate of change of the dimensions (population growth rate), and changes in
the distributions of individuals' states.
The properties of populations change all the time, and the rate of change can
vary from very low to high. Even in populations that do not change in density, the
individuals change and are replaced. They are born, grow and reproduce (or not), and
die. These changes in the state of individuals can be summarized as rates of change,
such as birth rate and mortality rate, or the proportion of individuals growing to a
particular size in an interval of time, etc. These demographic processes are direct
causes for the changes (or lack of it) in the population's dimensions, composition and
dynamics.
73
Demographic processes are abstractions, derived from actual changes in the
state of the individuals. They are calculated as the proportion of individuals in a
particular stage who manage to get to the next stage. Each individual experiences a
different rate of change, in accordance with its general condition, its past and its
genotype. Vital rates are demographic processes averaged over groups of individuals
(according to age, size, or stage). Vital rates include birth rate, survivorship, growth,
and fertility or fecundity. The states of individuals and the rates that form the
connections between them, determine the life-cycle of the population.
3. Population and environment
Two different populations of the same species differ first of all in their vital
rates, since they express how individuals respond to environmental variation. For
example, comparing a population of a particular animal species in a rich and a poor
habitat regarding food availability, we will usually see that population growth rate in
the rich place is higher than in the poorer place. This is because individuals survive
better, grow faster, attain reproductive maturity faster, and produce more offspring
when there is more food.
Environmental factors that affect demographic processes are very diverse and
can be divided in many ways. Categories are not exclusive: some factors may appear
in more than one category. The following division is based on the properties of the
factors and their effects on the organisms.
a) Environmental conditions - states of the environment that affect organisms, but are
not consumed by them: pH, temperature, air humidity (including their variation).
b) Resources - physical commodities (material or energy in any form, including other
organisms), which are supplied by the environment and consumed by the organism;
resources are at least as diverse as the organisms that require them.
c) Structures - availability of sites where individuals can perform their essential
functions (shelter, nesting, foraging, mating and recruitment sites); sites can be
viewed as a structural sort of resource.
74
d) Interactions with other organisms - all relationships with other organisms except
consuming another as resource; interactions include (the passive side of) predation,
herbivory and parasitism, and competition for resources and structures; besides
negative interactions, they can be positive as well (facilitation, mutualism).
e) Internal regulation - effects of the population itself (or some of its members) on the
way environmental factors affect the organisms. (Strictly speaking this is not an
environmental factor, although for each member of a population the other members
are part of its environment.) Processes affected this way are called density-dependent.
Density-dependence can be positive or negative, depending on whether density of the
population reduces or enlarges the effect of the environmental factor. Intraspecific
competition is
a
negatively
density-dependent
process,
and
operates
on resource acquisition.
4. Explaining population phenomena
The logical relations between environmental factors and the demography and
properties of a population are shown in Fig.1. A factor influences one or
more demographic processes within the population. This implies that a change in the
level of the factor causes a response of a vital rate (survival, growth, reproduction) so
that it becomes higher or lower. This is another way of saying that the factor operates
on individuals, and changes their ability to survive, grow and reproduce. Finally, the
demographic processes shape the entire population's properties such as composition
and
density,
and
its
dynamics.
Fig. 1. Relations between environmental factors,
the demography and properties of a population,
75
and internal regulation.
A simple example is a population of animals that consume parts of plants in
their habitat. When there is a lot of plant growth, the animal population grows
steadily. Another population, in a habitat with less plant growth, grows slower. This
is, for instance, because the individual animals grow slower on the average (or more
die or less become reproductive). This example does not include internal regulation,
however.
The situation becomes a little more complicated if we include the internal
regulation loop in Fig.1. A property of the population (its density, or the density of a
particular group of individuals) influences the way an environmental factor works. In
the herbivore population example, an increase in density (of adults, for instance)
causes a change in another demographic process (growth of the smaller animals, for
instance). This is the result of competition, by consumption of food by the adults, so
that there is less available for the others. The slower growth of the younger animals,
in turn, decreases a property of the population, its population growth rate. If this
regulatory process of negative density dependence continues, there is not sufficien
resource to support more individuals, so that the population stops growing and stays
near a particular density.
5. Hierarchy, mechanisms and context
The analysis of the example contains a explanation of a phenomenon
(dependence of the growth of the animal population on plant growth) including an
environmental factor (food supply) and a population property (population growth
rate). The explanation uses a number of mechanisms involving the individuals of the
population (growth of small animals as a function of food supply, and competition by
adults decreasing the supply). These are the details mentioned before.
The mechanisms do not happen at the same level of organization as the
phenomenon of population growth: the latter is observed by focusing on the properties
of the population, while the mechanisms only come in view when we focus
on individuals and follow them over a period of time. The time is the same as the one
over which we measured population growth.
76
It can be argued that this explanation is not complete at all - there are still a lot
of questions. For instance: how come the animals grow less if there is less plant
growth? Do they eat less, or different things, with different digestibility? And, how do
adults bother the smaller ones? Are they faster to get at the food, or do they push the
smaller ones away? Answering these questions would add a lot of important
information, and deepens the understanding of the population phenomenon.
Answering them requires us to change our focus further, and study what individuals
do (feeding and interfering). We can even ask questions about their digestion, down to
the molecular level. The point is, that the more detailed the questions become, the
further we get from the original focus, and the less we add to the explanation. The
reason is, that we also are looking at a different time scale, because feeding behavior
and nutritional physiology have typically shorter time spans than growth of
individuals and their population.
We can also extend our study to higher levels of organization, which is
relevant
for
understanding
the context of
the
population
phenomenon
(the background). We can ask: How does the growth of the food plant vary in the
landscape? However, further looking for details about the causes of differences in
food plant growth may be irrelevant. Another set of questions that may help
understanding the context of the population phenomenon (the dependence of
population growth on food plant growth) is about its consequences. Again, we will
have to change our focus and look at the animal community, to see if other animals
(predators, competitors) are affected.
The basic concepts of rate
An important concept in population ecology is the r/K selection theory. The
first variable is r (the intrinsic rate of natural increase in population size, density
independent) and the second variable is K (the carrying capacity of a population,
density dependent). An r-selected species (e.g., many kinds of insects, such as aphids)
is one that has high rates of fecundity, low levels of parental investment in the young
and high rates of mortality before individuals reach maturity. Evolution favors
productivity in r-selected species. In contrast, a K-selected species (such as humans)
has low rates of fecundity, high levels of parental investment in the young, and low
77
rates of mortality as individuals mature. Evolution in K-selected species favors
efficiency in the conversion of more resources into fewer offspring.
The intrinsic Rate of Natural increase
The rate of natural increase (RNI) is a statistic calculated by subtracting
the crude death rate from the crude birth rate of a given region. This rate gives
demographers an idea of how a certain country's population is growing. RNI excludes
in-migration and out-migration, giving an indication of population growth based only
on births and deaths. RNI can indicate what stage of the Demographic Transition
Model (DTM) a country is in. Trends in RNI can predict a country's economic
stability, level of development, and other things. Developing countries typically have
higher RNI values as they have limited infrastructure and access to healthcare which
limits them to unregulated fertility levels. These countries also have higher incidence
of disease and poor health outcomes leading to more deaths on top of the already high
fertility. Developing countries are therefore in the earlier stages of the DTM with high
fertility levels. This leads to developing countries to have high rates of natural
increase. Developed countries have lower RNI values because they are usually more
technologically advanced and have the necessary steps put into place to limit fertility.
They also have better access to healthcare and the resources necessary to combat
disease. Developed countries are there in the later stages of the DTM with low
fertility levels. This usually results in developed countries having lower RNI values.
The concept of carrying capacity
The carrying capacity of an environment is the maximum population size of a
biological species that can be sustained in that specific environment, given the
food, habitat, water, and other resources available. In population ecology, carrying
capacity is defined as the environment's maximal load, which is different from
the concept of population equilibrium, which may be far below an environment's
carrying capacity.[1] The effect of carrying capacity on population dynamics may be
modelled with a logistic function.
78
The specific reason why a population stops growing is known as
a limiting or regulating factor. The difference between the birth rate and the death
rate is the "natural increase". If the population of a given organism is below the
carrying capacity of a given environment, this environment could support a positive
natural increase; should it find itself above that threshold the population typically
decrease. Thus, the carrying capacity is the maximum number of individuals of a
species that an environment can support. Population size decreases above carrying
capacity due to a range of factors depending on the species concerned, but can include
insufficient space, food
supply,
or sunlight.
The
carrying
capacity
of
an environment may vary for different species. Carrying capacity was originally used
to determine the number of animals that could graze on a segment of land. The idea
has recently been applied to humans in the context of environmentalism. For
the human population variables such as sanitation and medical care are sometimes
considered as part of the environment.
Utilization of Learning
1.
2.
3.
4.
What are the properties of the population?
How are the basic concepts of rate?
What is the intrinsic Rate of Natural increase?
How are the concepts of carrying capacity?
Supplementary
Essentials of Ecology eBooks (Available in Google Classroom)
http://www.bgu.ac.il
https://en.wikipedia.org/wiki/Rate_of_natural_increase
79
Learning Resource Materials
Chapter 4: Community Ecology
Lesson 1: Interaction between Two Species and Strategy of Ecosystem Development
Target Outcomes
At the end of the lesson, you are expected to:
1. list the types of interaction between two species;
2. understand coevolution;
3. illustrate evolution of cooperation: group selection;
4. understand the interspecific competition and coexistence;
5. understand the positive/negative interactions: predation, herbivore, parasitism,
and allelopathy;
6. explain positive interactions: commensalism, cooperation, and mutualism;
7. understand the concepts of habitat, ecological niche, and guild;
8. explain biodiversity;
9. understand the community structure in past ages; and
10. explain the relationship of populations and communities to ecosystems and
landscapes.
Abstraction
The types of interaction between two species
Organisms live within an ecological community, which is defined as an
assemblage of populations of at least two different species that interact directly and
indirectly within a defined geographic area (Agrawal et al. 2007; Ricklefs 2008;
Brooker et al. 2009). Species interactions form the basis for many ecosystem
properties and processes such as nutrient cycling and food webs. The nature of these
interactions can vary depending on the evolutionary context and environmental
conditions in which they occur. As a result, ecological interactions between individual
organisms and entire species are often difficult to define and measure and are
frequently dependent on the scale and context of the interactions (Harrison & Cornell
80
2008; Ricklefs 2008; Brooker et al. 2009). Nonetheless, there are several classes of
interactions among organisms that are found throughout many habitats and
ecosystems. Using these classes of interactions as a framework when studying an
ecological community allows scientists to describe naturally occurring processes and
aids in predicting how human alterations to the natural world may affect ecosystem
properties
and
processes.
At the coarsest level, ecological interactions can be defined as either intra-specific or
inter-specific. Intra-specific interactions are those that occur between individuals of
the same species, while interactions that occur between two or more species are
called inter-specific interactions. However, since most species occur within
ecological communities, these interactions can be affected by, and indirectly
influence, other species and their interactions. The ones that will be discussed in this
article are competition, predation, herbivory and symbiosis. These are not the only
types of species interactions, just the most studied — and they are all parts of a larger
network of interactions that make up the complex relationships occurring in nature.
Competition is most typically considered the interaction of individuals that
vie for a common resource that is in limited supply, but more generally can be defined
as the direct or indirect interaction of organisms that leads to a change in fitness when
the organisms share the same resource. The outcome usually has negative effects on
the weaker competitors. There are three major forms of competition. Two of
them, interference competition and exploitation competition, are categorized as
real competition. A third form, apparent competition, is not. Interference
competition occurs directly between individuals, while exploitation competition and
apparent competition occur indirectly between individuals (Holomuzki et. al 2010).
Predation requires one individual, the predator, to kill and eat another
individual, the prey .In most examples of this relationship, the predator and prey are
both animals; however, protozoans are known to prey on bacteria and other
protozoans and some plants are known to trap and digest insects (for example, pitcher
plant). Typically, this interaction occurs between species (inter-specific); but when it
occurs within a species (intra-specific) it is cannibalism. Cannibalism is actually
quite common in both aquatic and terrestrial food webs (Huss et al. 2010;
Greenwood et al. 2010). It often occurs when food resources are scarce, forcing
81
organisms of the same species to feed on each other. Surprisingly, this can actually
benefit the species (though not the prey) as a whole by sustaining the population
through times of limited resources while simultaneously allowing the scarce resources
to rebound through reduced feeding pressure (Huss et al. 2010). The predator-prey
relationship can be complex through sophisticated adaptations by both predators and
prey, in what has been called an "evolutionary arms race." Typical predatory
adaptations are sharp teeth and claws, stingers or poison, quick and agile bodies,
camouflage coloration and excellent olfactory, visual or aural acuity. Prey species
have evolved a variety of defenses including behavioral, morphological,
physiological, mechanical, life-history synchrony and chemical defenses to avoid
being preyed upon (Aaron, Farnsworth et al. 1996, 2008).
Another interaction that is much like predation is herbivory, which is when an
individual feeds on all or part of a photosynthetic organism (plant or algae), possibly
killing it (Gurevitch et al. 2006). An important difference between herbivory and
predation is that herbivory does not always lead to the death of the individual.
Herbivory is often the foundation of food webs since it involves the consumption of
primary producers (organisms that convert light energy to chemical energy through
photosynthesis). Herbivores are classified based on the part of the plant consumed.
Granivores eat seeds; grazers eat grasses and low shrubs; browsers eat leaves from
trees or shrubs; and frugivores eat fruits. Plants, like prey, also have evolved
adaptations to herbivory. Tolerance is the ability to minimize negative effects
resulting from herbivory, while resistance means that plants use defenses to avoid
being consumed. Physical (for example, thorns, tough material, sticky substances) and
chemical adaptations (for example, irritating toxins on piercing structures, and badtasting chemicals in leaves) are two common types of plant defenses (Gurevitch et al.
2006)
Symbiosis is an interaction characterized by two or more species living
purposefully in direct contact with each other. The term "symbiosis" includes a broad
range of species interactions but typically refers to three major types: mutualism,
commensalism and parasitism. Mutualism is a symbiotic interaction where both or all
individuals
benefit
from
the
relationship.
Mutualism
can
be
considered obligate or facultative. (Be aware that sometimes the term "symbiosis" is
used specifically to mean mutualism.) Species involved in obligate mutualism cannot
survive without the relationship, while facultative mutualistic species can survive
82
individually when separated but often not as well (Aaron et al. 1996). For example,
leafcutter ants and certain fungi have an obligate mutualistic relationship. The ant
larvae eat only one kind of fungi, and the fungi cannot survive without the constant
care of the ants. As a result, the colonies activities revolve around cultivating the
fungi. They provide it with digested leaf material, can sense if a leaf species is
harmful to the fungi, and keep it free from pests. A good example of a facultative
mutualistic relationship is found between mycorrhizal fungi and plant roots. It has
been suggested that 80% of vascular plants form relationships with mycorrhizal fungi
(Deacon 2006). Yet the relationship can turn parasitic when the environment of the
fungi is nutrient rich, because the plant no longer provides a benefit (Johnson et al.
1997). Thus, the nature of the interactions between two species is often relative to the
abiotic conditions and not always easily identified in nature.
Commensalism is an interaction in which one individual benefits while the
other is neither helped nor harmed. For example, orchids (examples of epiphytes)
found in tropical rainforests grow on the branches of trees in order to access light, but
the presence of the orchids does not affect the trees. Commensalism can be difficult to
identify because the individual that benefits may have indirect effects on the other
individual that are not readily noticeable or detectable. If the orchid from the previous
example grew too large and broke off the branch or shaded the tree, then the
relationship would become parasitic.
Parasitism occurs when one individual, the parasite, benefits from another
individual, the host, while harming the host in the process. Parasites feed on host
tissue or fluids and can be found within (endoparasites) or outside (ectoparasites) of
the host body (Holomuzki et al. 2010). For example, different species of ticks are
common ectoparasites on animals and humans. Parasitism is a good example of how
species interactions are integrated. Parasites typically do not kill their hosts, but can
significantly weaken them; indirectly causing the host to die via illness, effects on
metabolism, lower overall health and increased predation potential (Holomuzki et al.
2010).
The coevolution
Coevolution occurs when two or more species reciprocally affect each
other's evolution through the process of natural selection. The term sometimes is used
83
for two traits in the same species affecting each other's evolution, as well as geneculture coevolution.
Charles Darwin mentioned evolutionary interactions between flowering
plants and insects in On the Origin of Species (1859). Although he did not use the
word coevolution, he suggested how plants and insects could evolve through
reciprocal evolutionary changes. Naturalists in the late 1800s studied other examples
of how interactions among species could result in reciprocal evolutionary change.
Beginning in the 1940s, plant pathologists developed breeding programs that were
examples of human-induced coevolution. Development of new crop plant varieties
that were resistant to some diseases favored rapid evolution in pathogen populations
to overcome those plant defenses. That, in turn, required the development of yet new
resistant crop plant varieties, producing an ongoing cycle of reciprocal evolution in
crop plants and diseases that continues to this day.
Coevolution as a major topic for study in nature expanded rapidly after the
middle 1960s, when Daniel H. Janzen showed coevolution between acacias and ants
(see below) and Paul R. Ehrlich and Peter H. Raven suggested how coevolution
between plants and butterflies may have contributed to the diversification of species
in both groups. The theoretical underpinnings of coevolution are now well-developed
(e.g., the geographic mosaic theory of coevolution), and demonstrate that coevolution
can play an important role in driving major evolutionary transitions such as the
evolution of sexual reproduction or shifts in ploidy. More recently, it has also been
demonstrated that coevolution can influence the structure and function of ecological
communities, the evolution of groups of mutualists such as plants and their
pollinators, and the dynamics of infectious disease.
Each party in a coe-volutionary relationship exerts selective pressures on the
other, thereby affecting each other's evolution. Coevolution includes many forms
of mutualism, host-parasite, and predator-prey relationships between species, as well
as competition within or between species. In many cases, the selective pressures drive
an evolutionary arms race between the species involved. Pairwise or specific
coevolution, between exactly two species, is not the only possibility; in multi-species
coevolution, which is sometimes called guild or diffuse coevolution, several to many
species may evolve a trait or a group of traits in reciprocity with a set of traits in
another species, as has happened between the flowering plants and pollinating insects
84
such as bees, flies, and beetles. There are a suite of specific hypotheses on the
mechanisms by which groups of species coevolve with each other.
Domestication, a special mode of evolution, can offer a unique insight how
multiple species evolve. Domestication is a process of human, based on own needs,
select particular traits, which fit the local environments. Condensed tannins can
trigger bitter and unpleasant perceptions by binding to type 2 taste receptors
(TAS2Rs). In East and South Africa, non-taster farmers (carrying ancestral TAS2R4
and TAS2R5) selected sorghum cultivars with high level of condensed tannins in
seeds to deter Quelea quelea, while in West Africa with less pressure from Q. quelea,
taster farmers (carrying derived TAS2R4 and TAS2R5) selected non-tannin sorghum
for better food. Coevolution is primarily a biological concept, but researchers have
applied it by analogy to fields such as computer science, sociology, and astronomy.
Evolution of cooperation: group selection
Social behaviours such as altruism and group relationships can impact many
aspects
of
population
dynamics,
such
as intraspecific
competition and interspecific interactions. In 1871, Darwin argued that group
selection occurs when the benefits of cooperation or altruism between subpopulations
are greater than the individual benefits of egotism within a subpopulation. This
supports the idea of multilevel selection, but kinship also plays an integral role
because many subpopulations are composed of closely related individuals. An
example of this can be found in lions, which are simultaneously cooperative and
territorial. Within a pride, males protect the pride from outside males, and females,
who are commonly sisters, communally raise cubs and hunt. However, this
cooperation seems to be density dependent. When resources are limited, group
selection favours prides that work together to hunt. When prey is abundant,
cooperation is no longer beneficial enough to outweigh the disadvantages of altruism,
and hunting is no longer cooperative.
Interactions between different species can also be affected by multilevel
selection. Predator-prey relationships can also be affected. Individuals of certain
monkey species howl to warn the group of the approach of a predator. The evolution
of this trait benefits the group by providing protection, but could be disadvantageous
85
to the individual if the howling draws the predator's attention to them. By affecting
these interspecific interactions, multilevel and kinship selection can change the
population dynamics of an ecosystem.
Multilevel selection attempts to explain the evolution of altruistic behaviour in
terms of quantitative genetics. Increased frequency or fixation of altruistic alleles can
be accomplished through kin selection, in which individuals engage in altruistic
behaviour to promote the fitness of genetically similar individuals such as siblings.
However, this can lead to inbreeding depression, which typically lowers the overall
fitness of a population. However, if altruism were to be selected for through an
emphasis on benefit to the group as opposed to relatedness and benefit to kin, both the
altruistic trait and genetic diversity could be preserved. However, relatedness should
still remain a key consideration in studies of multilevel selection. Experimentally
imposed multilevel selection on Japanese quail was more effective by an order of
magnitude on closely related kin groups than on randomized groups of individuals.
The interspecific competition and coexistence
Major focus in community ecology is about understanding the factors
underlying species coexistence (Carrete et al). When dealing with competition
between native and exotic species, the competitive exclusion of the ‘weaker’ species
can have consequences for biodiversity conservation (Carrete et al). It is important to
know whether this kind of interaction between species leads to exclusion of one
species or results in their co-existence (Sommer & Worm, 2002). Food resources are
always limited and maintained below the carrying capacity of the surrounding
environment to avoid the population exploitation. Species living in the same habitat
would have a problem of overlap in their food resources due to their limited
availability. When this happens, the two species compete and tries to drive the other
species away. This does not mean that the other species cannot survive in that habitat;
it can exist by developing certain adaptive features. A detailed research is conducted
on inter-specific competition and coexistence by Morrison, 2002 on three species,
namely Caenobita clypeatus (Herbst), Brachymyrmex obscurior Forel and
Dorymyrmex pyramicus Roger. Out of these three species, B. obscurior Forel and D.
pyramicus Roger are two different ant species and C. clypeatus is a Hermit Crab. This
86
inter-specific competition is between these three species, wherein either of the ant
species interacts with the crab but not both.
The available food resources for them are majorly overlapped, considering the
fact that all these three species are generalist scavengers. So, competition between
these species develops for the limited food resources. The studies were done for four
years and it was noted that C. clypeatus is good in recognizing its food source very
quickly while the B. obscurior recognizes the food source rather slowly. So, C.
clypeatus has advantage of getting to its food source earlier than the B. obscurior.
However, it so happens that B. obscurior finally would be successful in having the
food source. The reason is that once B. obscurior identified the source, it assists
several workers along with it so that they can defeat any other species coming for the
food source. These workers are generally aggressive and start attacking the other
species near to the food sources. Considering the above fact, it becomes obvious that
C. clypeatus would be successful in reaching first to its food source but would be
driven from the source once B. obscurior identifies the source. The data plots obtained
from the experiments done on these species were shown in Fig. 1 (taken from
Morrison, 2002). From the figure you can observe that in initial stages, C. clypeatus
number reaching to its baits is maximum, but then dominated by the B. obscurior in
later stages.
The other ant species D. pyramicus is also the competitor to C. clypeatus but
this is not as successful as B. obscurior. It’s mainly because unlike B. obscurior
D.pyramicus does not assist workers along with it and when contradicted with C.
clypeatus, it can be easily driven off. But still D. pyramicus has the ability to locate
the food source at the earliest like C. clypeatus but could not drive off the other
competitors like B. obscurior.
The positive/negative interactions: predation, herbivore, parasitism, and
allelopathy.
Although mutualisms are common in all biological communities, they occur
side by side with a wide array of antagonistic interactions. As life has evolved, natural
selection has favoured organisms that are able to efficiently extract energy and
nutrients from their environment. Because organisms are concentrated packages of
energy and nutrients in themselves, they can become the objects of antagonistic
87
interactions. Moreover, because resources often are limited, natural selection also has
favoured the ability of organisms to compete against one another for them. The result
has been the evolution of a great diversity of lifestyles. This diversity can be
categorized in any number of ways, but the edges of all the categories blend with one
another. Evolution continues to mix all the different kinds of interspecific interactions
into novel ways of life.
One way of understanding the diversity of antagonistic interactions is through
the
kinds
of
hosts
or prey that
species
attack. Carnivores attack
animals, herbivores attack plants, and fungivores attack fungi. Other species are
omnivorous, attacking a wide range of plants, animals, and fungi. Regardless of the
kinds of foods they eat, however, there are some general patterns in which species
interact. Parasitism, grazing, and predation are the three major ways in which species
feed on one another. The parasite lives on and feeds off its host, usually decreasing
the host’s ability to survive but not killing it outright. Grazing species are not as
closely tied to their food source as parasites and often vary their diet between two or
more species without directly killing them. Predators, however, capture and kill
members of other species for food.
Parasitism
Types of parasites
Parasitism is thought to be the most common way of life, and parasitic
organisms may account for as many as half of all living species. Examples include
pathogenic fungi and bacteria, plants that tap into the stems or roots of other plants,
insects that as larvae feed on a single plant, and parasitic wasps. Parasites live in or on
a single host throughout either a stage in their lives or their entire life span, thereby
decreasing the survival or reproduction of their hosts. This lifestyle has arisen many
times throughout evolution. The most species-rich groups of organisms are parasites,
which, in becoming specialized to live off their hosts alone, eventually become
genetically distinct from their species, sometimes to the degree that they are
considered a new species (speciation).
88
One common type of parasite is the parasitoid, an insect whose larvae feed and
develop within or on the bodies of other arthropods. Each parasitoid larva develops on
a single individual and eventually kills that host. Most parasitoids are wasps, but some
flies and a small number of beetles, moths, lacewings, and even one caddisfly species
have evolved to be parasitoids. Parasitoids alone number about 68,000 named species,
and most parasitoids have yet to be named and described. Realistic estimates of the
total number of described and undescribed parasitoid species are about 800,000.
The number of species of insects that develop as nymphs or larvae on a single
plant host may outnumber the parasitoids. There is currently a great deal of debate
concerning the number of species worldwide, and this debate centres on the number
of plant-feeding insect species, many of which inhabit the canopies of tropical trees.
These species have been almost impossible to collect until recently when techniques
allowing access to the canopies have been adapted from mountain-climbing methods.
All ecologists and systematists working on these estimates agree that there are at least
a few million plant-feeding insect species, but the estimates range from 2 to 30
million.
Estimates of the number of pathogenic fungi, parasitic nematodes, and other
parasitic groups also have increased as ecological and molecular studies are revealing
many previously unrecognized species. Continued work on biodiversity worldwide
will allow better estimates to be made of the Earth’s inventory of species, which is a
major prerequisite for understanding the role of parasites in the organization of
communities and in the conservation of diversity.
Specialization in parasites
It is now evident that the parasitic lifestyle often favours extreme
specialization to a single host or a small group of hosts. Living for a long period of
time on a single host, a parasite must remain attached within or on its host, avoid the
defenses of its host, and obtain all its nutrition from that host. Unlike grazers or
predators, parasites cannot move from host to host, supplementing their diet with a
variety of foods.
89
Estimates of the number of species worldwide have risen sharply in recent
decades owing to research revealing parasitic species to be much more specific to one
host species than previously realized. What once may have been considered a single
parasitic species attacking many different host species has often turned out to be a
group of very similar, yet distinct, parasitic species, each specialized to its own host.
This speciation occurs because different parasitic populations become adapted to
living on different hosts and coping with the defenses of these hosts. Over time, many
of these different parasite populations evolve into genetically distinct species. It is
through the specialization of individuals of a species onto different hosts, ultimately
resulting in speciation, that parasitism appears to have become the most common way
of life on Earth.
For example, swallowtail butterflies (Papilio) include more than 500 species
worldwide. In most species an adult female lays her eggs on a host plant, and, after
they hatch, the caterpillars complete their development by feeding parasitically on that
plant. In North America there are two groups of these butterflies that have evolved to
use different hosts: the tiger swallowtail group and the Old World swallowtail group
(Papilio machaon). In the Old World swallowtail group are several species that feed
on plants in the carrot family Apiaceae (also called Umbelliferae), with different
populations feeding on different plant species. However, one species within this
group, the Oregon swallowtail (Papilio oregonius), has become specialized to feed on
tarragon sagebrush (Artemisia dracunculus), which is in the plant family Asteracaea
(Compositae of some sources). Among the tiger swallowtail group, various members
have become specialized to different plant hosts. The eastern tiger swallowtail
(Papilio glaucus) has a long list of recorded hosts, but it is now known that the
northern and southern populations are adapted to different plant species, and these
populations cannot develop on the others’ hosts.
Alternation among hosts
Although many parasitic species complete all developmental stages on a single
host individual, thousands of other parasitic species alternate between two or more
host species, specializing on a different host species at each developmental stage.
Many parasites, from a diverse array of species such as certain viruses, flatworms,
90
nematodes, and aphids, specialize on different host species at different stages of
development. Among aphids alone at least 2,700 species alternate among hosts.
Parasites have evolved by three major evolutionary routes to alternate among
two or more hosts. Some parasite species have evolved to alternate between their final
host and an intermediate host, or vector, that transfers the parasite from one final host
to another: the malarial parasite Plasmodium falciparum alternates between a final
human host and an intermediate mosquito host by which the parasite is transferred
from one person to another. The parasite uses the mosquito as a mobile hypodermic
syringe. Examples of a similar kind of transmission between a final host and an
intermediate host with piercing mouthparts occur in many other species. Viruses,
rickettsias, protozoa, and nematodes all have species that are transmitted between
vertebrates through biting flies. Some viruses and other parasites are similarly
transmitted between plant species by aphids, whose piercing mouthparts transmit the
parasites directly into plant tissues while the aphids are feeding.
Other parasites alternate between a host and the predator that eats it. These
parasites have turned an evolutionary problem (being killed along with their host) into
an evolutionary opportunity (being transferred to the predator and continuing to feed).
As it develops, the parasite attacks hosts higher in the food chain, alternating
between herbivore and predator or between an intermediate and a top predator in the
food chain. Many parasites alternate between snails or other invertebrates and
vertebrate predators that feed upon these invertebrates; others alternate among
vertebrate species. The pork tapeworm (Taenia solium), for example, alternates
between pigs and humans in societies in which improperly cooked pork is eaten.
Still other parasites employ wings, wind, or water to alternate between hosts.
Many aphid species alternate between a summer host and a winter host by producing
winged individuals that fly to the new host. Rust fungi such as wheat stem rust can be
carried between hosts by wind currents, and the parasite Schistosoma mansoni, which
causes the disease schistosomiasis, alternates between Biomphalaria snails and
humans by moving through water.
The different ways by which host species are linked to parasites contribute to the
complex web of interactions that shape the structure of communities. The effect of
91
parasitism on the dynamics of populations and the organization of communities is still
one of the most underexplored topics in ecology.
Predation
Predation differs from both parasitism and grazing in that the victims are killed
immediately. Predators therefore differ from parasites and grazers in their effects on
the dynamics of populations and the organization of communities. As with parasitism
and grazing, predation is an interaction that has arisen many times in many taxonomic
groups worldwide. Bats that capture insects in flight, starfish that attack marine
invertebrates, flies that attack other insects, and adult beetles that scavenge the ground
for seeds are all examples of the predatory lifestyle. Cannibalism, in which
individuals of the same species prey on one another, also has arisen many times and is
common in some animal species. Some salamanders and toads have tadpoles that
occur in two forms, one of which has a specialized head that allows it to cannibalize
other tadpoles of the same species.
Competition
Competition is a powerful form of interaction in the organization of
communities, but it differs from other forms of antagonistic and mutualistic
relationships in that no species benefits from the interaction. In competitive
interactions, species evolve either to avoid each other, to tolerate the presence of the
other, or to aggressively exclude the other.
Types of competition
Species compete for almost every conceivable kind of resource, and the same
two species may compete for different resources in different environments. Holenesting birds compete for tree holes, plant species compete for pollinators and seed
dispersers, and male birds compete for preferred sites to defend as territories for
92
attracting females. Species may compete for many resources simultaneously, but often
one resource, called the limiting resource because it limits the population growth of
each species, is the focus of competition. Moreover, the ways in which species
compete vary with the resources. In some cases, species compete by capturing
resources faster than their competitors (exploitation competition). Some plant species,
for example, are able to extract water and nutrients from the soil faster than
surrounding species. In other cases, the two species physically interfere with one
another (interference competition) by aggressively attempting to exclude one another
from particular habitats.
Commensalism and other types of interaction
In commensal interactions, one species benefits and the other is unaffected.
The commensal organism may depend on its host for food, shelter, support, transport,
or a combination of these. One example of commensalism involves a small crab that
lives inside an oyster’s shell. The crab enters the shell as a larva and receives shelter
while it grows. Once fully grown, however, it is unable to exit through the narrow
opening of the two valves, and so it remains within the shell, snatching particles of
food from the oyster but not harming its unwitting benefactor. Another form of
commensalism occurs between small plants called epiphytes and the large tree
branches on which they grow. Epiphytes depend on their hosts for structural support
but do not derive nourishment from them or harm them in any way.
Many other kinds of interaction, however, range from antagonism to
commensalism to mutualism, depending on the ecological circumstances. For
example, plant-feeding insects may have large detrimental effects on plant survival
or reproduction if they attack small or nonvigorous plants but may have little or no
effect on large or vigorous plants of the same species. Some human diseases may
cause only temporary discomfort or be life-threatening, depending on the age and
physical condition of the person.
No interaction between species fits neatly into the categories of antagonism,
commensalism, or mutualism. The interaction depends on the genetic makeup of both
93
species and the age, size, and physical condition of the individuals. Interactions may
even depend on the composition of the community in which the interaction takes
place. For example, the moth Greya politella pollinates the flowers of a small herb
called the prairie star (Lithophragma parviflorum). The female moth pollinates while
she lays eggs (oviposits) in the corolla of the flower. As she pushes her abdomen
down into a flower, pollen adheres to her. She flies on to the next flower to lay more
eggs, where some of the pollen rubs off onto the stigma of the flower, causing
pollination to occur. Although this unusual pollination mechanism is very effective in
some local populations, in other communities different pollinators such as bee flies
and bees are so common that their visits to the flowers swamp the pollination efforts
of the moths. As a result, pollination by the moths makes up a very tiny proportion of
all the pollinator visits that occur within that community and probably has little effect
on plant reproduction or natural selection. This moth, therefore, is a commensal in
some populations and a mutualist in others, depending on the local assemblage of
pollinator species.
The Coevolutionary Process
As pairs or groups of species interact, they evolve in response to each other.
These reciprocal evolutionary changes in interacting species are called coevolutionary
processes, one of the primary methods by which biological communities are
organized. Through coevolution local populations of interacting species become
adapted to one another, sometimes even evolving into new species.
Predator-prey interactions
In an evolutionary arms race, natural selection progressively escalates the
defenses and counter defences of the species. The thick calcareous shells of many
marine mollusks and the powerful drilling appendages and musculature of their
predators are thought to have coevolved through this process of escalation. A similar
example of coevolution has occurred in the endemic mollusks and crabs in Lake
Tanganyika. The mollusks in this lake have much thicker shells than other freshwater
94
mollusks, and the endemic crab that feeds on them has much larger chelae (pincerlike
claws) than other freshwater crabs. Differences between these mollusks and crabs and
the freshwater species throughout the world to which they are related appear to be due
to coevolution rather than any unique nutrient or mineral conditions in this lake.
Parasite-host interactions
Parasites and their hosts engage in a similar evolutionary arms race, although
in the past parasitologists believed this not to be the case. Instead, parasites were
thought
to
evolve
gradually
toward
reduced
antagonism—having
a
less detrimental effect on their hosts. The degree of virulence was sometimes regarded
as an indicator of the age of the relationship: a very virulent relationship, which
resulted in the swift demise of the host, was considered new. Research in
population biology and evolutionary ecology, however, provided evidence that
contradicts this view. Parasite-host interactions are now understood to evolve toward
either increased or decreased antagonism, depending on several important ecological
factors.
The density of the host population and the transmission rate of the parasite are
two of the most important of these ecological factors. The density of the host species
determines how often the opportunity arises for a parasite to move from one host to
another; the transmission rate of the parasite determines how easily a parasite can
move between hosts when the opportunity does arise. Only some parasites are
transmitted easily between hosts. If the host occurs at a high density and the
transmission rate of the parasite is also high, then natural selection favours increased
virulence in the parasite. Being easily transmissible and having many host individuals
to infect, the parasite can multiply quickly and escape to new hosts before it kills its
current host and dies along with it. Some forms (genotypes) of the parasite will
already contain or will develop mutations that increase the speed and proficiency of
this process. By producing more organisms that survive, the mutated form of the
parasite will outcompete those parasites with the original genotype that are not able to
maximize the opportunity to infect the greatest number of hosts. After several
generations, many more parasites with enhanced virulence will exist, and this
genotype can be said to be favoured by natural selection. If host population density
95
remains high, the parasite genotype that confers the most virulence will become the
only form of the parasite in that population.
Positive interactions: commensalism, cooperation, and mutualism
In ecology,
a biological
interaction is
the
effect
that
a
pair
of organisms living together in a community have on each other. They can be either of
the same species (intraspecific interactions), or of different species (interspecific
interactions). These effects may be short-term, like pollination and predation, or longterm; both often strongly influence the evolution of the species involved. A long-term
interaction is called a symbiosis. Symbioses range from mutualism, beneficial to both
partners, to competition, harmful to both partners.[1] Interactions can be indirect,
through intermediaries such as shared resources or common enemies. This type of
relationship can be shown by net effect based on individual effects on both organisms
arising out of relationship.
Several recent studies have suggested non-trophic species interactions such as
habitat modification and mutualisms can be important determinants of food web
structures. However, it remains unclear whether these findings generalize across
ecosystems, and whether non-trophic interactions affect food webs randomly, or
affect specific trophic levels or functional groups.
Although biological interactions, more or less individually, were studied
earlier, Edward Haskell (1949) gave a integrative approach to the thematic, proposing
a classification of "co-actions", later adopted by biologists as "interactions". Close and
long-term interactions are described as symbiosis; symbioses that are mutually
beneficial are called mutualistic.
Commensalism is a long-term biological interaction (symbiosis) in which
members of one species gain benefits while those of the other species neither benefit
nor are harmed. This is in contrast with mutualism, in which both organisms benefit
from each other; amensalism, where one is harmed while the other is unaffected;
and parasitism, where one is harmed and the other benefits. The commensal (the
species that benefits from the association) may obtain nutrients, shelter, support, or
locomotion from the host species, which is substantially unaffected. The commensal
relation is often between a larger host and a smaller commensal; the host organism is
unmodified, whereas the commensal species may show great structural adaptation
96
consistent with its habits, as in the remoras that ride attached to sharks and other
fishes. Remoras feed on their hosts' fecal matter,while pilot fish feed on the leftovers
of their hosts' meals. Numerous birds perch on bodies of large mammal herbivores or
feed on the insects turned up by grazing mammals.
Mutualism describes
the
ecological interaction between
two
or
more species where each species has a net benefit. [1] Mutualism is a common type of
ecological interaction. Prominent examples include most vascular plants engaged in
mutualistic interactions with mycorrhizae, flowering plants being pollinated by
animals, vascular plants being dispersed by animals, and corals with zooxanthellae,
among many others. Mutualism can be contrasted with interspecific competition, in
which each species experiences reduced fitness, and exploitation, or parasitism, in
which one species benefits at the "expense" of the other. Mutualism is often conflated
with
two
other
types
of
ecological
phenomena: cooperation and symbiosis. Cooperation refers to increases in fitness
through within-species (intraspecific) interactions. Symbiosis involves two species
living in proximity and may be mutualistic, parasitic, or commensal, so symbiotic
relationships are not always mutualistic.
Mutualism plays a key part in ecology. For example, mutualistic interactions are
vital for terrestrial ecosystem function as more than 48% of land plants rely
on mycorrhizal relationships with fungi to provide them with inorganic compounds
and trace elements. As another example, the estimate of tropical forest trees with seed
dispersal mutualisms with animals ranges from 70–90%. In addition, mutualism is
thought to have driven the evolution of much of the biological diversity we see, such
as flower forms (important for pollination mutualisms) and co-evolution between
groups of species. However, mutualism has historically received less attention than
other
interactions
such
as predation and parasitism.
The
term mutualism was
introduced by Pierre-Joseph van Beneden in his 1876 book Animal Parasites and
Messmates.
Cooperation
It is the process of groups of organisms working or acting together for
common,
mutual,
or
some
underlying
benefit,
as
opposed
to
working
in competition for selfish benefit. Many animal and plant species cooperate both with
97
other members of their own species and with members of other species
(symbiosis or mutualism). Cooperation is common in non-human animals. Besides
cooperation with an immediate benefit for both actors, this behaviour appears to occur
mostly between relatives. Spending time and resources assisting a related individual
may at first seem destructive to the organism's chances of survival but is actually
beneficial over the long-term. Since relatives share part of their genetic make-up,
enhancing each other's chances of survival may actually increase the likelihood that
the helper's genetic traits will be passed on to future generations. The cooperative
pulling paradigm is an experimental design used to assess if and under which
conditions animals cooperate. It involves two or more animals pulling rewards
towards themselves via an apparatus they cannot successfully operate alone.
Some researchers assert that cooperation is more complex than this. They
maintain that helpers may receive more direct, and less indirect, gains from assisting
others than is commonly reported. Furthermore, they insist that cooperation may not
solely be an interaction between two individuals but may be part of the broader goal
of unifying populations.
The concepts of habitat, ecological niche, and guild
The habitat of an organism is the place where it lives, or the place where one
would go to find it. The ecological niche, however, includes not only the physical
space occupied by an organism but also its functional role in the community (its
trophic position, for instance) and its position in environmental gradients of
temperature, moisture, pH, soil, and other conditions of existence. These three aspects
of the ecological niche can be conveniently designated as the spatial or habitat niche,
the trophic niche, and the multidimensional or hyper-volume niche.
Consequently, the ecological niche of an organism not only depends on where
it lives but also includes the sum total of its environmental requirements. The concept
of niche is most useful, and quantitatively most applicable, in terms of differences
between species (or the same species at two or more locations or times) in one or a
few major (operationally significant) features.
The dimensions most often quantified are niche breadth and niche overlap
with neighbors. Groups of species with comparable roles and niche dimensions within
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a community are termed guilds. Species that occupy the same niche in different
geographical regions (continents and major oceans) are termed ecological equivalents.
The term habitat is used widely, not only in ecology but elsewhere. Thus, the
habitat of the water backswimmer (Notonecta) and the water boatman (Corixa) is the
shallow, vegetation-choked area (littoral region) of ponds and lakes; one would go
there to collect these particular water bugs. However, the two species occupy very
different trophic niches, as the backswimmer is an active predator, whereas the water
boatman feeds largely on decaying vegetation. The ecological literature is replete with
examples of coexisting species that use different energy sources.
If the habitat is the “address” of the organism, niche is its “profession,” its trophic position in food webs, how it lives and interacts with the physical environment
and with other organisms in its community. Habitat may also refer to the place occupied by an entire community. For example, the habitat of the sand sage grassland
community is the series of ridges of sandy soil occurring along the north sides of
rivers in the southern Great Plains of the United States.
Habitat in this case consists mostly of physical or abiotic complexes, whereas
habitat for the water bugs includes living and non-living objects. Thus, the habitat of
an organism or group of organisms (population) includes other organisms and the
abiotic environment.
The concept of ecological niche is not so generally understood outside the
field of ecology. Terms such as niche are difficult to define and quantify; the best
approach is to consider the component concepts historically. Joseph Grinnell (1917,
1928) used the word niche “to stand for the concept of the ultimate distributional unit,
within which each species is held by its structural and instinctive limitations … no
two species in the same general territory can occupy for long identically the same
ecological niche.”
Thus, Grinnell thought of the niche mostly in terms of the microhabitat, or
what is now called the spatial niche. Charles Elton (1927) was one of the first to begin
using the term niche in the sense of the “functional status of an organism in its
community.” Because of Elton’s great influence on ecological thinking, it has become
99
generally accepted that niche is by no means a synonym for habitat. Because Elton
emphasized the importance of energy relations, his version of the concept is
designated the trophic niche.
G. E. Hutchinson (1957) suggested that the niche could be visualized as a
multidimensional space or hyper-volume within which the environment permits an
individual or species to survive indefinitely. Hutchinson’s niche, which can be
designated the multidimensional or hyper-volume niche, can be measured and
mathematically manipulated. For example, two-dimensional climographs, which
depict x- and y-axes of a particular species of bird and a fruit fly, could be expanded
as a series of coordinates (x-, y-, and z-axes) to include other environmental
dimensions.
Hutchinson (1965) also distinguished between the fundamental niche—the
maximum “abstractly inhabited hyper-volume” when the species is not constrained by
competition or other limiting biotic interactions—and the realized niche—a smaller
hyper-volume occupied under particular biotic constraints.
Perhaps a simple analogy from everyday human affairs will help to clarify
these overlapping and sometimes confusing ecological uses of the term niche. To
become acquainted with a person in the human community, one would need to know,
first of all, his or her address, (where she or he could be found). “Address” would
represent habitat. To “know” the person, however, one would want to know
something about his or her occupation, interests, associates, and role in community
life.
All this information would be analogous to that person’s niche. Thus, in the
study of organisms, learning the habitat is just the beginning. To determine the status
of the organism within the natural community, one would need to know something of
its activities, especially its nutrition; energy sources and resource partitioning;
relevant population attributes, such as intrinsic rate of increase and fitness; and
finally, the organism’s effect on other organisms with which it comes into contact,
and the extent to which it modifies or can modify important operations in the
ecosystem.
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In a classic investigation in the history of ecology, Mac Arthur (1958)
compared the niches of four species of American warblers (Parulidae) that all breed in
the same macrohabitat (a spruce forest) and all feed on insects but forage and nest in
different parts of the spruce tree. MacArthur constructed a mathematical model,
which consisted of a set of competition equations in a matrix from which competition
coefficients were calculated for the interaction between each species and any of the
other three.
Thus, niches of similar species associated together in the same habitat can be
precisely compared when only a few operationally significant measurements are involved. Two species proved especially competitive, so that if either were absent, the
other might be expected to move into the vacated niche space.
The term guild is often used for groups or clusters of species, such as
MacArthur’s warblers, that have similar or comparable roles in the community; Root
(1967) first suggested this definition. Wasps parasitizing a herbivore population,
nectar-feeding insects, snails living in the forest floor litter, and vines climbing into
the canopy of a tropical forest are all examples of guilds. The guild is a convenient
unit for studies of interactions among species, but it can also be treated as a functional
unit in community analysis, thus making it unnecessary to consider every species as a
separate entity.Examination of guilds or species that fail to coexist can illustrate what
aspects of resource use contribute to the competitive exclusion principle. Niche
partitioning frequently relates to resource partitioning or resource use.
MacArthur and Levins (1967) and Schoener (1983) noted that perhaps the
most operational approach to the study of competition and niche overlap is to focus on
consumable resources, or factors that serve as surrogates for those resources, such as
differences in microhabitats. Winemiller and Pianka (1990) have used this approach
to identify nonrandom patterns and clusters regarding the way that species use
resources in a guild.
Measurements of morphological features of larger plants and animals can
often be used as indices in the comparison of niches. Van Valen (1965), for example,
found that variations in the length and breadth of a bird’s bill (the bill, of course,
reflects the type of food eaten) provide an index of niche width; the coefficient of
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variation in bill width was found to be greater in island populations of six species of
birds than in mainland populations, corresponding with the greater niche width (wider
variety of habitat occupied and food eaten) on islands, where competing species are
fewer.
Grant (1986) was able to separate feeding niches of Galapagos finches by
measuring beak morphology. He found that differences in beak size correlated to
differences in diet. Within the same species, competition is often greatly reduced
when different stages in the life history of the organism occupy different niches; for
example, the tadpole functions as a herbivore and the adult frog as a carnivore in the
same pond. Niche segregation may even occur between sexes. In woodpeckers of the
genus Picoides, males and females differ in bill size and in foraging behavior. In
hawks, some weasels, and many insects, the sexes differ markedly in size and,
therefore, in the dimensions of their food niche.
Both nutrients and toxic chemicals introduced into natural ecosystems can be
expected to alter the niche relations of species most severely affected by the perturbation. In a long-term (11-year) experimental study of the effect of applying N-P-K
commercial fertilizer and municipal sludge to old-field vegetation, W. P. Carson and
Barrett (1988) and Brewer et al. (1994) reported that niche width was significantly
enhanced for summer annuals, especially Ambrosia trifida, A. artemisiifolia, and
Setaria faberii, which increased their coverage at the expense of perennials such as
Solidago canadensis.
Ecologically equivalent species, which occupy similar niches in different geographical regions, tend to be closely related taxonomically in contiguous regions, but
are often not related in noncontiguous regions. The species composition of communities differs widely in different floral and faunal regions, but similar ecosystems develop equivalent functional niches wherever physical conditions are similar,
regardless of geographical location.
The equivalent functional niches are occupied by whatever biological groups
happen to make up the flora and fauna of the region. Thus, a grassland ecosystem
develops wherever there is a grassland climate, but the species of grass and grazers
may be quite different, especially when the regions are widely separated by barriers.
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The large kangaroos of the Australian grassland are the ecological equivalents of the
bison and pronghorn of the North American grassland (both now largely replaced by
domesticated grazers).
Biodiversity
Biodiversity is a term used to describe the enormous variety of life on Earth. It
can be used more specifically to refer to all of the species in one region or ecosystem.
Biodiversity refers to every living thing, including plants, bacteria, animals, and
humans. Scientists have estimated that there are around 8.7 million species of plants
and animals in existence. However, only around 1.2 million species have been
identified and described so far, most of which are insects. This means that millions of
other organisms remain a complete mystery.
Over generations, all of the species that are currently alive today have evolved
unique traits that make them distinct from other species. These differences are what
scientists use to tell one species from another. Organisms that have evolved to be so
different from one another that they can no longer reproduce with each other are
considered different species. All organisms that can reproduce with each other fall
into one species.
Scientists are interested in how much biodiversity there is on a global scale,
given that there is still so much biodiversity to discover. They also study how many
species exist in single ecosystems, such as a forest, grassland, tundra, or lake. A single
grassland can contain a wide range of species, from beetles to snakes to antelopes.
Ecosystems that host the most biodiversity tend to have ideal environmental
conditions for plant growth, like the warm and wet climate of tropical regions.
Ecosystems can also contain species too small to see with the naked eye. Looking at
samples of soil or water through a microscope reveals a whole world of bacteria and
other tiny organisms.
Some areas in the world, such as areas of Mexico, South Africa, Brazil, the
southwestern United States, and Madagascar, have more biodiversity than others.
Areas with extremely high levels of biodiversity are called hotspots. Endemic species
—species that are only found in one particular location—are also found in hotspots.
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All of the Earth’s species work together to survive and maintain their
ecosystems. For example, the grass in pastures feeds cattle. Cattle then produce
manure that returns nutrients to the soil, which helps to grow more grass. This manure
can also be used to fertilize cropland. Many species provide important benefits to
humans, including food, clothing, and medicine.
Much of the Earth’s biodiversity,
human consumption and
other
activities
however, is in jeopardy due to
that
disturb
and
even
destroy
ecosystems. Pollution, climate change, and population growth are all threats to
biodiversity. These threats have caused an unprecedented rise in the rate of
species extinction. Some scientists estimate that half of all species on Earth will be
wiped out within the next century. Conservation efforts are necessary to preserve
biodiversity and protect endangered species and their habitats.
The community structure in past ages
Community structure is the ecologist's term for indicating what organisms are
present in a given environment, in what numbers, and how they relate to each other.
Another way to look at a community is as a collection of niches or slots that
organisms can fit into in order to “make a living.” The term community is rather
arbitrary. Its boundaries can be as wide or as narrow as one chooses to make them.
For example, a rocky-shore community could refer to a thousand miles of coastline or
to a kelp community in a band tens to hundreds of feet wide on that coast, or the
kelp epiphyte community could refer to those organisms growing on single kelp
plants. Reasonably sharp community boundaries are required for such a designation,
but even that criterion is sometimes rather fuzzy. Traditionally, a biological
community is named for a dominant element or elements. An Acropora palmata reef
community is conspicuously dominated by that single coral species as a major
element of biomass or structure, controlling many other organisms by its presence.
A Batis–Distichlis salt marsh community
is
a
salt
marsh
in
which
the
saltwort Batis and the salt grass Distichlis more or less equally provide the primary
vegetation and therefore cover in the marsh.
Communities are composed of the species occupying a site. Identification of
patterns in community structure has been a major goal of ecological research.
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However, no standard approach for delimiting a site and describing or comparing
community structure has been adopted. Indices of species diversity, food web
structure, and functional group organization are three methods used to facilitate
comparison among communities.
Species diversity has two components: richness and evenness. Richness is the
number of species in the community, whereas evenness is a measure of relative
abundances. These two components can be represented by rank-abundance curves and
by diversity indices. Geometric rank-abundance curves characterize harsh or disturbed
habitats with a limited number of adapted species and strong dominance hierarchy,
whereas log and broken stick models characterize more stable habitats with higher
species accumulation and greater evenness in abundance among species. A number of
diversity indices and similarity indices have been developed to integrate richness and
evenness in a variable that can be compared among community types.
Food web structure represents the network of pairwise interactions among the
species in the community. A number of food web attributes have been proposed,
based on limited taxonomic resolution of insects and other arthropods. These
hypotheses are being challenged as greater resolution of arthropod taxonomy reveals
networks of interactions within this diverse group.
Functional group organization reflects combination of species on the basis of
functional responses to environmental variables or effects on ecological processes,
regardless of taxonomic affiliation. This approach has become popular because it
simplifies species diversity in an ecologically meaningful way. However, the
allocation of species to functional groups is based on particular objectives and is
therefore arbitrary to the extent that each species represents a unique combination of
functional responses or effects.
The noncomparable descriptions of communities based on these three
approaches, compounded by the variety of arthropod sampling techniques, each with
its unique biases, have hindered comparison of community structure among habitat
types.
Many
taxa
show latitudinal
gradients in
abundance,
with species
richness increasing toward the equator. However, the climate gradient thought to
underlie this trend is correlated with latitudinal gradients in habitat area and
productivity. Some taxonomic groups are more diverse within biogeographic
realms of origin or where resources have been available over longer time periods.
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Some functional groups are more abundant in certain biomes (e.g., pollinators in
diverse tropical habitats and detritivores and wood borers in habitats with greater
organic matter or wood accumulation).
Habitat area and stability, resource availability, and species interactions are
major factors that affect community structure. Habitat area affects the pool of species
available and the heterogeneity of habitat conditions and resources. Habitat stability
determines the length of time available for species accumulation, assortment, and
species packing. Species richness generally increases with resource availability, up to
a point at which the most adapted species competitively suppress other species.
Species interactions often affect persistence in a particular habitat. Colonists cannot
survive unless their host resources are available. Competition, predation, and
mutualism also affect species directly and indirectly. Indirect effects often are at least
as important as direct effects. Keystone species have effects on community structure
or ecosystem processes that are disproportionate to their numbers or biomass.
Keystone species include predators that focus on the most abundant prey species,
thereby reducing competition among prey species and maintaining more species than
would co-exist in the absence of the predator. Some herbivorous insects function
as keystone species by selectively reducing abundance of dominant host species and
facilitating persistence of nonhosts. Trophic cascades reflect top-down effects of
predators reducing prey abundance, thereby increasing abundance of the trophic
level supporting the prey.
The relationship of populations and communities to ecosystems and landscapes
Landscape ecology is the science of studying and improving relationships
between ecological processes in the environment and particular ecosystems. This is
done within a variety of landscape scales, development spatial patterns, and
organizational levels of research and policy. Concisely, landscape ecology can be
described
as
the
science
of landscape
diversity as
the
synergetic
result
of biodiversity and geodiversity. As a highly interdisciplinary field in systems
science,
landscape
ecology
integrates biophysical and analytical approaches
with humanistic and holistic perspectives
across
the natural
sciences and social
sciences. Landscapes are spatially heterogeneous geographic areas characterized by
diverse interacting patches or ecosystems, ranging from relatively natural terrestrial
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and aquatic systems such as forests, grasslands, and lakes to human-dominated
environments including agricultural and urban settings. The most salient
characteristics of landscape ecology are its emphasis on the relationship among
pattern, process and scale, and its focus on broad-scale ecological and environmental
issues. These necessitate the coupling between biophysical and socioeconomic
sciences. Key research topics in landscape ecology include ecological flows in
landscape mosaics, land use and land cover change, scaling, relating landscape pattern
analysis with ecological processes, and landscape conservation and sustainability.
[7]
Landscape ecology also studies the role of human impacts on landscape diversity in
the development and spreading of new human pathogens that could trigger epidemics.
Nowadays, at least six different conceptions of landscape ecology can be
identified:
one
group
tending
toward
the
more
disciplinary
concept
of ecology (subdiscipline of biology; in conceptions 2, 3, and 4) and another group—
characterized by the interdisciplinary study of relations between human societies and
their environment—inclined toward the integrated view of geography (in conceptions
1, 5, and 6):
1.
Interdisciplinary
analysis
of
subjectively
defined
landscape
units (e.g. Neef School): Landscapes are defined in terms of uniformity in
land use. Landscape ecology explores the landscape's natural potential in
terms of functional utility for human societies. To analyse this potential, it is
necessary to draw on several natural sciences.
2. Topological ecology at the landscape scale 'Landscape' is defined as a
heterogeneous land area composed of a cluster of interacting ecosystems
(woods, meadows, marshes, villages, etc.) that is repeated in similar form
throughout. It is explicitly stated that landscapes are areas at a kilometres
wide human scale of perception, modification, etc. Landscape ecology
describes and explains the landscapes' characteristic patterns of ecosystems
and investigates the flux of energy, mineral nutrients, and species among their
component ecosystems, providing important knowledge for addressing landuse issues.
3.
Organism-centred, multi-scale topological ecology (e.g. John A. Wiens):
Explicitly rejecting views expounded by Troll, Zonneveld, Naveh, Forman &
107
Godron, etc., landscape and landscape ecology are defined independently of
human perceptions, interests, and modifications of nature. 'Landscape' is
defined – regardless of scale – as the 'template' on which spatial patterns
influence ecological processes. Not humans, but rather the respective species
being studied is the point of reference for what constitutes a landscape.
4. Topological ecology at the landscape level of biological organisation (e.g.
Urban et al.): On the basis of ecological hierarchy theory, it is presupposed
that nature is working at multiple scales and has different levels of
organisation which are part of a rate-structured, nested hierarchy. Specifically,
it is claimed that, above the ecosystem level, a landscape level exists which is
generated and identifiable by high interaction intensity between ecosystems, a
specific interaction frequency and, typically, a corresponding spatial scale.
Landscape ecology is defined as ecology that focuses on the influence exerted
by spatial and temporal patterns on the organisation of, and interaction
among, functionally integrated multispecies ecosystems.
5. Analysis of social-ecological systems using the natural and social sciences
and humanities (e.g. Leser; Naveh; Zonneveld): Landscape ecology is defined
as an interdisciplinary super-science that explores the relationship between
human societies and their specific environment, making use of not only
various natural sciences, but also social sciences and humanities. This
conception is grounded in the assumption that social systems are linked to
their specific ambient ecological system in such a way that both systems
together form a co-evolutionary, self-organising unity called 'landscape'.
Societies' cultural, social and economic dimensions are regarded as an integral
part of the global ecological hierarchy, and landscapes are claimed to be the
manifest systems of the 'Total Human Ecosystem' (Naveh) which
encompasses both the physical ('geospheric') and mental ('noospheric')
spheres.
6.
Ecology guided by cultural meanings of lifeworldly landscapes (frequently
pursued in practice[31] but not defined, but see, e.g., Hard; Trepl): Landscape
ecology is defined as ecology that is guided by an external aim, namely, to
maintain and develop lifeworldly landscapes. It provides the ecological
knowledge necessary to achieve these goals. It investigates how to sustain and
108
develop those populations and ecosystems which (i) are the material 'vehicles'
of lifeworldly, aesthetic and symbolic landscapes and, at the same time, (ii)
meet societies' functional requirements, including provisioning, regulating,
and supporting ecosystem services. Thus landscape ecology is concerned
mainly with the populations and ecosystems which have resulted from
traditional, regionally specific forms of land use.
Utilization of Learning
Answer the following questions;
1.
2.
3.
4.
5.
What are the types of interaction between two species?
What is coevolution?
Illustrate the evolution of cooperation: group selection.
What is the interspecific competition and coexistence?
List down the positive/negative interactions between predation,
herbivore, parasitism,
and allelopathy.
6. List down the positive interactions on commensalism, cooperation, and
mutualism.
7. Illustrate the concepts of habitat, ecological niche, and guild?
8. What is biodiversity?
9. Explain the community structure in past ages.
10. Explain the relationship of populations and communities to ecosystems
and landscapes.
Supplementary
https://www.youtube.com/watch?v=LmUoC_VFmg8
https://www.nature.com
https://en.wikipedia.org
https://www.nationalgeographic.org/
Lesson 2: Ecosystem Development
109
Target Outcomes
At the end of the lesson, you are expected to:
1.
2.
3.
4.
understand the strategy of ecosystem development;
explain the concept of the climax;
explain the evolution of the Biosphere;
differentiate microevolution with Macroevolution, Artifioal Selection, and
Genetic Engineering; and
5. understand the relevance of ecosystem development to human ecology.
Abstraction
The strategy of ecosystem development
Odum suggests the application of successional theory to ecological system
studies in order to better understand the development of ecosystems. According to the
author, until this article was written in 1969, the majority of the understanding of the
how ecosystems developed relied upon descriptive data and “highly theoretical
assumptions” with very little attempt to experimentally test hypotheses. Odum
identifies the lack of experimental work in ecosystem ecology is the misinterpretation
of the definition of succession. Stressing the idea that succession consists of a
complex interaction of processes. In applying a successional model to ecosystem
studies, he uses a tabular model to outline “components and stages of development at
the ecosystem level as a means of emphasizing those aspects of ecological succession
that can be accepted on the basis of present knowledge, those that require more study,
and those that have special relevance to human ecology”.
Definition of Succession
Odum defines succession according to three parameters:
(1)
It is an orderly process of community development that is reasonably directional
and, therefore predictable.
110
(2)
It results from modification of the physical environment by the community; that is,
succession is community-controlled even though the physical environment determines
the pattern, the rate of change, and often sets limits as to how far development can go.
(3)
It culminates in a stabilized ecosystem in which maximum biomass (or high
information content) and symbiotic function between organisms are maintained per
unit of available energy.
Bioenergetics of Ecosystem Development
Bioenergetics of the ecosystem are defined by attributes 1-5. These attributes
refer to changes within the ecosystem itself. The theory in this is that as the ratio
(P/R) of the rate of primary production or total (gross) photosynthesis (P) and the rate
of community respiration (R) approaches 1, succession occurs. “energy fixed tends to
be balanced by the energy cost of maintenance…in the mature or ‘climax’ ecosystem’
(597[263]).
Components of Succession in a Laboratory Microcosm and a Forest
Odum then discusses the above bioenergetics theory using laboratory aquatic
microsystems from ponds cultured by Beyers (1963). During the initial stages of the
experiment, “the daytime production (P) exceeds nighttime respiration (R), so that
biomass (B) accumulates in the system” (597). After the initial bloom, both rates
decline eventually becoming nearly equal with the B/P ratio increasing as the
microenvironment approaches steady state. Although it refers to changes brought by
biological processes within the ecosystem, Odum also stresses the importance of
outside influence on Eutrophication. In the case of lakes, nutrients are imported to the
lake from the watershed. Thus, he concludes that more oligotrophic conditions can be
restored by slowing of nutrient input. This, in turn, can be used to deal with water
pollution problems. However, this can only be achieved through functional studies of
the larger landscape.
Food Chains and Food Webs
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Changes in the food chains also occur as ecosystems develop. Low diversity in
the early stages of ecosystem development maintain a simple and linear food chain.
As the system matures, the chains become more and more complex creating food
webs. Within these webs, the Odum found that the majority of biological energy flow
follows a detritus pathway (598).
Diversity and Succession
Within (items 8-11), Odum lists four components of diversity: (8) species
diversity – variety component; (9) species diversity – equability component; (10)
biochemical diversity; and (11) stratification and spatial heterogeneity (pattern
diversity). These kinds of diversity are suggested by the author to follow different
developmental avenues that lead to stability of the system. According to the author,
the diversity-stability relationship needs better understood. Is diversity necessary for
the stability of the ecosystem?
Nutrient Cycling
As a system matures, its capacity to entrap nutrients becomes greater (599). In
this discussion, Odum cites Bormann and Likens (1967) and questions whether or not
the increased water yield of the stream is a good thing. He suggests that reducing the
vegetation around the stream would be accompanied by a greater loss of nutrients, and
thus affect those systems downstream. However, the nutrient retention of the biomass
at this point (1969) still needs to be tested.
Selection Pressure: Quantity versus Quality
Citing MacArther and Wilson (1967), Odum suggests that species with high
rates of reproduction and growth are more likely to survive in uncrowded situations
earlier in ecosystem development, while competitive species with low growth would
fare better in a more diverse environment in the later stages of the system.
112
Understanding the implications of the dynamics of populations could have potential
implications for the adaptations that will occur with overcrowding that is occurring
with human populations.
Overall Homeostasis
The review of ecosystems outlined by Odum was in an attempt to discuss the
complex nature of the processes that interact with the system (600). Understanding
how the entirety of the system as a whole contributes to a better grasp on the nature of
ecosystems. This leads to the question of how these systems age: as they get older do
they return to a state of “vulnerability”?
Relevance of Ecosystem Development Theory to Human Ecology
Figure 1 is an interpretation of the human view of nature. According to Odum,
humans look at the landscape and look for ways to achieve high production of the
biomass and fail to see it as a limited resource. In other words, humans see a high P/B
efficiency when in reality an ecosystem has a high B/P efficiency.
According to Odum, the human preoccupation with production has caused them to
forget that the landscape is not merely a “supply depot” but a home where humans
and other organisms must live (600). In other words, are humans getting “too much of
a good thing” when they focus on only one aspect of the landscape rather than the
impacts on the environment as a whole.
Pulse Stability
There are cases when recurring changes in the ecosystem result in that system
to remain in some intermediate stage between development and maturity. This is
known as pulse stability. Organisms in the everglades, for example, have adapted to
fluctuating periods wet (flooded) and dry periods. In this system wood storks only
breed when water levels are falling but will not nest when conditions are still wet. A
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situation such as this only works in a system if the community is complete. Any
sudden change (such as those caused by people) results in the inability of the
ecosystem to adapt and reach any point of stability.
Prospects for a Detritus Agriculture
Natural conditions are also better for growing food. Current agricultural
practices of selection of plants for rapid growth and edibility make them vulnerable
for attacks by insects (602). This, in turn, results in the use of harmful pesticides.
Odum suggests that reversing the strategy and selecting plants that have adapted their
own insecticides from using delayed consumption of detritus would result in a much
clean and stable environment. This would also result in the utilization of natural
systems rather than modification and destruction.
The Compartment Model
Odum concludes that a compartmentalization strategy of systems needs to be
utilized so that “growth type, steady state, and intermediate-type ecosystems can be
linked with urban and industrial areas for mutual benefit” (602). While this would
require laws governing zoning procedures, it would limit the impact of humans on the
environment. If nothing else, it would provide the opportunity for an increased study
and awareness of how much people depend on the environment.
The concept of the climax
According to classical ecological theory, succession stops when the sere has
arrived at an equilibrium or steady state with the physical and biotic environment.
Barring major disturbances, it will persist indefinitely. This end point of succession is
called climax. climax community, or climatic climax community, is a historic term for
a boreal forest community of plants, animals, and fungi which, through the process
of ecological succession in the development of vegetation in an area over time, have
reached a steady state. This equilibrium was thought to occur because the climax
community is composed of species best adapted to average conditions in that area.
The term is sometimes also applied in soil development. Nevertheless, it has been
114
found that a "steady state" is more apparent than real, particularly if long-enough
periods of time are taken into consideration. Notwithstanding, it remains a useful
concept.
The idea of a single climax, which is defined in relation to regional climate, originated
with Frederic Clements in the early 1900s. The first analysis of succession as leading
to something like a climax was written by Henry Cowles in 1899, but it was Clements
who used the term "climax" to describe the idealized endpoint of succession.
The evolution of the Biosphere
The biosphere is the space on and near the earth's surface that contains and
supports living organisms and ecosystems. It is typically subdivided into the
lithosphere, atmosphere, and hydrosphere. The lithosphere is the earth's surrounding
layer composed of solid soil and rock, the atmosphere is the surrounding gaseous
envelope, and the hydrosphere refers to liquid environments such as lakes and oceans,
occurring between the lithosphere and atmosphere. The biosphere's creation and
continuous evolution result from physical, chemical, and biological processes. To
study these processes a multi-disciplinary effort has been employed by scientists from
such fields as chemistry, biology, geology, and ecology.
Microevolution
with
Macroevolution,
Arteficial
Selection,
and
Genetic
Engineering
Microevolution is the change in allele frequencies that occurs over time within
a population.[1] This change is due to four different processes: mutation, selection
(natural and artificial), gene flow and genetic drift. This change happens over a
relatively short (in evolutionary terms) amount of time compared to the changes
termed macroevolution.
Population genetics is the branch of biology that provides the mathematical
structure for the study of the process of microevolution. Ecological genetics concerns
itself with observing microevolution in the wild. Typically, observable instances
of evolution are examples of microevolution; for example, bacterial strains that
have antibiotic resistance. Microevolution may lead to speciation, which provides the
raw material for macroevolution. Macroevolution is guided by sorting of interspecific
115
variation ("species selection"), as opposed to sorting of intraspecific variation in
microevolution.[3] Species selection may occur as (a) effect-macroevolution, where
organism-level traits (aggregate traits) affect speciation and extinction rates, and (b)
strict-sense species selection, where species-level traits (e.g. geographical range)
affect speciation and extinction rates.[4] Macroevolution does not produce evolutionary
novelties, but it determines their proliferation within the clades in which they evolved,
and it adds species-level traits as non-organismic factors of sorting to this process.
Mutations are changes in the DNA sequence of a cell's genome and are caused
by radiation, viruses, transposons and mutagenic chemicals, as well as errors that
occur during meiosis or DNA replication. Errors are introduced particularly often in
the process of DNA replication, in the polymerization of the second strand. These
errors can also be induced by the organism itself, by cellular processes such
as hypermutation. Mutations can affect the phenotype of an organism, especially if
they occur within the protein coding sequence of a gene. Error rates are usually very
low—1 error in every 10–100 million bases—due to the proofreading ability of DNA
polymerases.[8][9] (Without proofreading error rates are a thousandfold higher; because
many viruses rely on DNA and RNA polymerases that lack proofreading ability, they
experience higher mutation rates.) Processes that increase the rate of changes in DNA
are called mutagenic: mutagenic chemicals promote errors in DNA replication, often
by interfering with the structure of base-pairing, while UV radiation induces
mutations by causing damage to the DNA structure. [10] Chemical damage to DNA
occurs naturally as well, and cells use DNA repair mechanisms to repair mismatches
and breaks in DNA—nevertheless, the repair sometimes fails to return the DNA to its
original sequence.
In organisms that use chromosomal crossover to exchange DNA and
recombine genes, errors in alignment during meiosis can also cause mutations.
[11]
Errors in crossover are especially likely when similar sequences cause partner
chromosomes to adopt a mistaken alignment making some regions in genomes more
prone to mutating in this way. These errors create large structural changes in DNA
sequence—duplications, inversions or deletions of entire regions, or the accidental
exchanging of whole parts between different chromosomes (called translocation).
Mutation can result in several different types of change in DNA sequences;
these can either have no effect, alter the product of a gene, or prevent the gene from
116
functioning. Studies in the fly Drosophila melanogaster suggest that if a mutation
changes a protein produced by a gene, this will probably be harmful, with about 70
percent of these mutations having damaging effects, and the remainder being either
neutral or weakly beneficial.[12] Due to the damaging effects that mutations can have
on cells, organisms have evolved mechanisms such as DNA repair to remove
mutations.[5] Therefore, the optimal mutation rate for a species is a trade-off between
costs of a high mutation rate, such as deleterious mutations, and the metabolic costs of
maintaining systems to reduce the mutation rate, such as DNA repair enzymes.
[13]
Viruses that use RNA as their genetic material have rapid mutation rates, [14] which
can be an advantage since these viruses will evolve constantly and rapidly, and thus
evade the defensive responses of e.g. the human immune system.
Mutations can involve large sections of DNA becoming duplicated, usually
through genetic recombination. These duplications are a major source of raw material
for evolving new genes, with tens to hundreds of genes duplicated in animal genomes
every million years. Most genes belong to larger families of genes of shared ancestry.
Novel genes are produced by several methods, commonly through the duplication and
mutation of an ancestral gene, or by recombining parts of different genes to form new
combinations with new functions.
Here, domains act as modules, each with a particular and independent
function, that can be mixed together to produce genes encoding new proteins with
novel properties. For example, the human eye uses four genes to make structures that
sense light: three for color vision and one for night vision; all four arose from a single
ancestral gene. Another advantage of duplicating a gene (or even an entire genome) is
that this increases redundancy; this allows one gene in the pair to acquire a new
function while the other copy performs the original function. Other types of mutation
occasionally create new genes from previously noncoding DNA.
Selection is the process by which heritable traits that make it more likely for
an organism to survive and successfully reproduce become more common in
a population over successive generations. It is sometimes valuable to distinguish
between naturally occurring selection, natural selection, and selection that is a
manifestation of choices made by humans, artificial selection. This distinction is
rather diffuse. Natural selection is nevertheless the dominant part of selection.
117
The natural genetic variation within a population of organisms means that
some
individuals
will
survive
more
successfully
than
others
in
their
current environment. Factors which affect reproductive success are also important, an
issue which Charles Darwin developed in his ideas on sexual selection.
Natural selection acts on the phenotype, or the observable characteristics of an
organism, but the genetic (heritable) basis of any phenotype which gives a
reproductive advantage will become more common in a population (see allele
frequency). Over time, this process can result in adaptations that specialize organisms
for particular ecological niches and may eventually result in the speciation (the
emergence of new species).
Natural selection is one of the cornerstones of modern biology. The term was
introduced by Darwin in his groundbreaking 1859 book On the Origin of Species,
[27]
in which natural selection was described by analogy to artificial selection, a
process by which animals and plants with traits considered desirable by human
breeders are systematically favored for reproduction. The concept of natural selection
was originally developed in the absence of a valid theory of heredity; at the time of
Darwin's writing, nothing was known of modern genetics. The union of
traditional Darwinian
evolution with
subsequent
discoveries
in classical and molecular genetics is termed the modern evolutionary synthesis.
Natural selection remains the primary explanation for adaptive evolution.
Genetic drift is the change in the relative frequency in which a gene variant
(allele) occurs in a population due to random sampling. That is, the alleles in the
offspring in the population are a random sample of those in the parents. And chance
has a role in determining whether a given individual survives and reproduces. A
population's allele frequency is the fraction or percentage of its gene copies compared
to the total number of gene alleles that share a particular form.
Genetic drift is an evolutionary process which leads to changes in allele
frequencies over time. It may cause gene variants to disappear completely, and
thereby reduce genetic variability. In contrast to natural selection, which makes gene
variants more common or less common depending on their reproductive success,
[29]
the changes due to genetic drift are not driven by environmental or adaptive
pressures, and may be beneficial, neutral, or detrimental to reproductive success.
118
The effect of genetic drift is larger in small populations, and smaller in large
populations. Vigorous debates wage among scientists over the relative importance of
genetic drift compared with natural selection. Ronald Fisher held the view that genetic
drift plays at the most a minor role in evolution, and this remained the dominant view
for several decades. In 1968 Motoo Kimura rekindled the debate with his neutral
theory of molecular evolution which claims that most of the changes in the genetic
material are caused by genetic drift.[30] The predictions of neutral theory, based on
genetic drift, do not fit recent data on whole genomes well: these data suggest that the
frequencies of neutral alleles change primarily due to selection at linked sites, rather
than due to genetic drift by means of sampling error.
The relevance of ecosystem development to human ecology
The human productive environment comprises early successional or growthtype ecosystems, such as croplands, pastures, tree plantations, and intensely managed
forests that provide food and fiber. Mature ecosystems, such as old-growth forests,
climax grasslands, and oceans, are more protective than productive. They stabilize
substrates, buffer air and water cycles, and moderate extremes in temperature and
other physical factors, while at the same time often providing products.
The third category of natural or semi-natural ecosystems, which bear the brunt
of assimilating the vast wastes produced by the urban-industrial and agricultural
systems, consists of waterways (inland and coastal), wetlands, and other intensely
stressed environments. Ecosystems in this admittedly arbitrary category are, in the
developmental sense, mostly in intermediate, eutrophicated, or arrested stages of
succession.
Partitioning the landscape into three environmental components—natural, domesticated, and fabricated—as is traditional with landscape architects, provides
another convenient way to consider the needs of and interrelations between these
necessary parts of our household. Although the urbanized or fabricated environment is
parasitic on the life-support environment (natural and domesticated) for basic
biological necessities (breathing, drinking, and eating), it does create and export other,
mostly non-biotic, resources, such as fertilizers, money, processed energy, and goods
that both benefit and put stress on the life-support environment. Much more can be
done to increase the resource output while reducing the stress and use of subsidies
necessary to maintain outputs from high-energy, densely populated “hot spots.”
119
However, no known feasible technology can substitute on a global scale for the basic
biotic life-support goods and services provided by natural ecosystems.
Utilization of Learning
Answer the following questions;
1.
What is the strategy of ecosystem development?
2.
What is the concept of the climax?
3.
Explain the evolution of the Biosphere.
4.
Differentiate microevolution with Macroevolution, Artifioal Selection, and
Genetic Engineering; and
5.
What is the relevance of ecosystem development to human ecology?
Supplementary
Essentials of Ecology eBooks (Available in Google Classroom)
http://unmecology.blogspot.com
https://science.jrank.org
https://en.wikipedia.org/wiki/Microevolution
http://www.ecologyessays.com/
Chapter 5: Landscape and Regional Ecology
Lesson 1: Landscape Ecology: Definition and Relation to Levels of organization
concept
120
Target Outcomes
At the end of the lesson, you are expected to;









explain landscape Ecology: Definition and Relation to Levels of organization
concept;
understand landscape elements;
describe biodiversity at the community and landscape levels;
understand island biogeography;
explain neutral theory;
illustrate temporal and spatial scale;
explain landscape geometry;
explain the concept of landscape sustainability; and
understand domesticated landscapes.
Abstraction
Landscape Ecology
Landscape ecology is the study of the pattern and interaction between
ecosystems within a region of interest, and the way the interactions affect
ecological processes, especially the unique effects of spatial heterogeneity on
these interactions. Historical Perspective
Throughout the history of ecology, scientists have observed variability
across time and space in the abiotic and biotic components of ecosystems. But
early ecologists did not have the technology or concepts to explicitly deal with
spatial heterogeneity, so there was a tendency to develop explanations by
grouping organisms into uniform and recognizable units. For example, scientists
were struck by the relatively consistent associations of plant species and grouped
vegetation into community types (Mueller-Dombois & Ellenberg 1974).
Compared to vegetation, where observed change was rather slow, observations of
fluctuating populations ranging from bacteria and protozoans in the laboratory to
snowshoe hares (Lepus americanus) in the boreal forest, led scientists to
121
mathematical theories that explicitly focused on temporal dynamics (Kingsland
1995). But the resulting models treated the environment as spatially
homogeneous. Such views of nature and the theory about dynamics led to
“equilibrium” concepts (May 1973) that dominated ecological thinking from the
1920s through the 1980s.
During the 1980s, advances in the accessibility of computing, remotely
sensed satellite and aerial imagery, development of geographic information
systems (GIS, ARC/INFO was first released in 1982), and spatial statistical
methods (Fortin & Dale 2005), enabled ecologists to observe and analyze spatial
heterogeneity ranging from local habitats to entire continents. The technology
enhanced a paradigm shift occurring in ecology and the emergence of landscape
ecology as a sub-discipline within ecology (Wu & Loucks 1995). Landscape
ecology specifically recognizes that disturbance, whether anthropogenic or caused
by natural processes, creates spatial heterogeneity that is the normal condition of
ecosystems. In landscape ecology particularly, a “non-equilibrium” view emerged,
that links disturbance in time and space to system structure and function in
feedback loops that influence the ecology and evolutionary trajectories in the
ecosystems. The International Association of Landscape Ecology was formed in
1982. In 1986, Forman and Godron published their seminal text on landscape
ecology. This work was important, not only because it outlined principles, but also
because it brought together the North American scientific interest — typically
focused on heterogeneity in ecosystems — with more anthropocentric scientific
traditions of geography, landscape architecture, and planning, rooted in the long
history of landscape alteration in Europe.
Landscape Elements
A landscape is the visible features of an area of land, its landforms, and
how they integrate with natural or man-made features.[1] A landscape includes the
physical
elements
of geophysical defined landforms such
as
(ice-
capped) mountains, hills, water bodies such as rivers, lakes, ponds and the sea,
living elements of land cover including indigenous vegetation, human elements
including different forms of land use, buildings, and structures, and transitory
elements such as lighting and weather conditions. Combining both their physical
122
origins and the cultural overlay of human presence, often created over millennia,
landscapes reflect a living synthesis of people and place that is vital to local and
national identity.
The character of a landscape helps define the self-image of the people who
inhabit it and a sense of place that differentiates one region from other regions. It
is the dynamic backdrop to people's lives. Landscape can be as varied as farmland,
a landscape park or wilderness. The Earth has a vast range of landscapes,
including the icy landscapes of polar regions, mountainous landscapes, vast arid
desert landscapes, islands, and coastal landscapes, densely forested or wooded
landscapes including past boreal forests and tropical rainforests, and agricultural
landscapes of temperate and tropical regions. The activity of modifying the visible
features of an area of land is referred to as landscaping.
There are several definitions of what constitutes a landscape, depending on
context.[2] In common usage however, a landscape refers either to all the visible
features of an area of land (usually rural), often considered in terms
of aesthetic appeal, or to a pictorial representation of an area of countryside,
specifically within the genre of landscape painting. When people deliberately improve
the aesthetic appearance of a piece of land—by changing contours and vegetation, etc.
—it is said to have been landscaped,[1] though the result may not constitute a
landscape according to some definitions.
The word landscape (landscipe or landscaef) arrived in England—and therefore
into the English language—after the fifth century, following the arrival of the AngloSaxons; these terms referred to a system of human-made spaces on the land. The
term landscape emerged around the turn of the sixteenth century to denote a painting
whose primary subject matter was natural scenery.[3] Land (a word from Germanic
origin) may be taken in its sense of something to which people belong (as in England
being the land of the English).[4] The suffix -scape is equivalent to the more common
English
suffix - ship.[4] The
roots
of - ship are
etymologically
akin
to
Old
English sceppan or scyppan, meaning to shape. The suffix -schaft is related to the
verb schaffen, so that -ship and shape are also etymologically linked. The modern
form of the word, with its connotations of scenery, appeared in the late sixteenth
century when the term landschap was introduced by Dutch painters who used it to
123
refer to paintings of inland natural or rural scenery. The word landscape, first
recorded in 1598, was borrowed from a Dutch painters' term. [5] The popular
conception of the landscape that is reflected in dictionaries conveys both a particular
and a general meaning, the particular referring to an area of the Earth's surface and the
general being that which can be seen by an observer.
Biodiversity at the community and landscape levels
The term biodiversity (from “biological diversity”) refers to the variety of life
on Earth at all its levels, from genes to ecosystems, and can encompass the
evolutionary, ecological, and cultural processes that sustain life. Biodiversity includes
not only species we consider rare, threatened, or endangered but also every living
thing—from humans to organisms we know little about, such as microbes, fungi, and
invertebrates.
At the Center for Biodiversity and Conservation, we include humans and
human cultural diversity as a part of biodiversity. We use the term “biocultural” to
describe the dynamic, continually evolving and interconnected nature of people and
place, and the notion that social and biological dimensions are interrelated. This
concept recognizes that human use, knowledge, and beliefs influence, and in turn are
influenced, by the ecological systems of which human communities are a part. This
relationship makes all of biodiversity, including the species, land and seascapes, and
the cultural links to the places where we live—be right where we are or in distant
lands—important to our wellbeing as they all play a role in maintaining a diverse and
healthy planet.
Island biogeography
Biogeography is the study of the geographic location of a species. Island
biogeography is the study of the species composition and species richness on islands.
Island biogeography is a study aimed at establishing and explaining the factors
that affect species diversity of a specific community. An island in this context, is not
just a segment of land surrounded by water. It is any area of habitat surrounded by
areas unsuitable for the species on the island. Other examples of "islands" include
124
dung piles, game preserves, mountain tops, and lakes. In 1967, ecologists Robert
MacArthur and E.O. Wilson, coined the Theory of Island Biogeography. This
theory attempted to predict the number of species that would exist on a newly created
island. It also explained how distance and area combine to regulate the balance
between immigration and extinction in an island population. Immigration is the
appearance of a new species in a community. Extinction is then the disappearance of a
species from a community. This relationship is known as "species turnover", states
that the equilibrium value for the island is proportional to the number of immigrants
that come to the island, and the loss of individuals due to emigration and extinction.
E.O. Wilson and R. MacArthur did several experiments and made several
predictions about the Theory of Island Biogeography. Some of their predictions
included (1)species richness tends toward an equilibrium value and (2) the
equilibrium value is the result of immigration, but emigration and extinction may also
occur.
The equilibrium value (equilibrium diversity value) of an island depends on the area
of the island- the larger the area the more resources there are on the island. Smaller
islands support smaller populations, and smaller populations are more likely to
become extinct. Here is where the Target Effect comes in play. The Target Effect
says that larger islands have higher immigration rates because they are a bigger target.
Three basic types of species-area relationships have been well defined and
demonstrated through various experiments within the field of ecology: "type-1"
investigates species richness vs. sample area in nested samples (within a defined
habitat or region), "type-2" is defined by examining the total species richness vs. total
area among habitats or regions differing in area, and "type-3" examines local species
richness in a sample of defined size among habitats or regions differing in area [1].
Another factor that determines the equilibrium diversity value is the distance
from the source as discussed below. For example, the immigration rate is higher at
closer islands than on islands that are further away from the mainland. Here is where
the Rescue Effect comes in mind. The rescue effect decreases the rate of extinction
due to recolonization and immigration. Immigration is a major contributor due to
increasing population size and the size of the genetic pool. These two factors can
reduce the probability that any particular species will become extinct [2].
125
Recolonization happens through two occurrences: Immigration and invasion;
immigration is the arrival of a new species to an area, while invasion is the arrival of a
species that already inhabits an area [3].
The last factor that contributes and/or determines the equilibrium diversity
value is the species richness of the source. Species richness is the number of species
in a community. Although islands are considered relatively new land, they can still
have a great deal of diversity on them over a few years. This concept comes from
the Time/Stability Hypothesis and to the Species-Area Effect which both say that
the older the land is/the longer the land has been around, the more diversity and the
more stable that land will contain. For example, islands may not be diverse right away
because they have not been around long enough for species to migrate onto that
particular land mass. The Species-Area Effect states that increased area results in
increase species equilibrium. However, this relationship is not linear. The following
equation describes this relationship: S=cAz, where S is the number of species, c is a
constant, A is the area, and z is the slope of the line (varies). Islands may be colonized
several different ways:(1) by hitchhiking on other species, (2)flying, (3) rafting, (4)
swimming, (5) wind, (6) and speciation. It takes time for the new islands to gain
several different species of animals due to several different aspects, but given enough
time the islands will obtain life on them and become more and more diverse.
Neutral theory
In the decades since its introduction, the neutral theory of evolution has
become central to the study of evolution at the molecular level, in part because it
provides a way to make strong predictions that can be tested against actual data. The
neutral theory holds that most variation at the molecular level does not affect fitness
and, therefore, the evolutionary fate of genetic variation is best explained by
stochastic processes. This theory also presents a framework for ongoing exploration
of two areas of research: biased gene conversion, and the impact of effective
population size on the effective neutrality of genetic variants. The evolution of living
organisms is the consequence of two processes. First, evolution depends on the
genetic variability generated by mutations, which continuously arise within
populations. Second, it also relies on changes in the frequency of alleles within
populations over time.
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The fate of those mutations that affect the fitness of their carrier is partly
determined by natural selection. On one hand, new alleles that confer a higher fitness
tend to increase in frequency over time until they reach fixation, thus replacing the
ancestral allele in the population. This evolutionary process is called positive or
directional selection. Conversely, new mutations that decrease the carrier's fitness
tend to disappear from populations through a process known as negative or purifying
selection.
Finally,
it
may
happen
that
a mutation is
advantageous
only
in heterozygotes but not in homozygotes. Such alleles tend to be maintained at an
intermediate frequency in populations by way of the process known as balancing
selection.
However, natural selection is not the only factor that can lead to changes
in allele frequency. For example, consider a theoretical population in which all
individuals, or genotypes, have exactly the same fitness. In this situation, natural
selection does not operate, because all genotypes have the same chance to contribute
to the next generation. Given that populations do not grow infinitely and that each
individual produces many gametes, it follows that only a fraction of the gametes that
are produced will succeed in developing into adults. Thus, in each generation, allelic
frequencies may change simply as a consequence of this random process of gamete
sampling. This process is called genetic drift. The difference between genetic drift and
natural selection is that changes in allele frequency caused by genetic drift are
random, rather than directional. Ultimately, genetic drift leads to the fixation of some
alleles and the loss of others.
But what about mutations that do not affect the fitness of individuals? These so-called
neutral mutations are not affected by natural selection and, hence, their fate is
essentially driven by genetic drift. Interestingly, Darwin himself recognized that some
traits might evolve without being affected by natural selection:
"Variations neither useful nor injurious would not be affected by natural selection,
and would be left either a fluctuating element, as perhaps we see in
certain polymorphic species, or would ultimately become fixed, owing to the nature
of the organism and the nature of the conditions." (Darwin, 1859)
It is important to note, however, that the impact of genetic drift is not limited
to neutral mutations. Because of genetic drift, most advantageous mutations are
eventually lost, whereas some weakly deleterious mutations may become fixed.
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Beyond selection and drift, biased gene conversion (BGC) is a third process
that can cause changes in allele frequency in sexual populations. BGC is linked
to meiotic
crossing-over.
When
crossing-over
occurs
between
two homologous chromosomes, the intermediate includes heteroduplex DNA—a
region in which one DNA strand is from one homologue and the other strand is from
the other homologue. Regardless of the ultimate resolution of the crossover
intermediate (in other words, whether the regions on either side of the crossover
junction recombine), base-pairing mismatches in the heteroduplex region must be
resolved. As a consequence, when a given locus resides in the heteroduplex region,
one allele can be "copied and pasted" onto the other one during gene conversion.
Temporal and spatial scale
Temporal comes from the Latin word temporalis which means "of time" and is
usually applied to words that mean not having much of it, such as the temp who
works at an office for a set amount of time, because temporary situations don't last
long. A less common word, temporality also means "having limited time," and it
rhymes with mortality! (Don't remind us.) Temporal implies "of this earth," too —
temporal boundaries keep us from being able to fly around the clouds, but spiritual
beings can zing around at will. Temporal can also refer to temples, the ones on the
side of your head that are probably aching by now. Temporal scale is habitat lifespan
relative to the generation time of the organism, and spatial scale is the distance
between habitat patches relative to the dispersal distance of the organism.
Spatial ecology studies the ultimate distributional or spatial unit occupied by
a species. In a particular habitat shared by several species, each of the species is
usually confined to its own microhabitat or spatial niche because two species in the
same general territory cannot usually occupy the same ecological niche for any
significant length of time.
In nature, organisms are neither distributed uniformly nor at random, forming
instead
some
sort
of spatial
pattern.[1] This
is
due
to
various
energy
inputs, disturbances, and species interactions that result in spatially patchy structures
or gradients. This spatial variance in the environment creates diversity in communities
of organisms, as well as in the variety of the observed biological and ecological
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events.[1] The type of spatial arrangement present may suggest certain interactions
within and between species, such as competition, predation, and reproduction.[2] On
the other hand, certain spatial patterns may also rule out specific ecological
theories previously thought to be true.[3]
Although spatial ecology deals with spatial patterns, it is usually based
on observational data rather than on an existing model.[2] This is because nature rarely
follows set expected order. To properly research a spatial pattern or population, the
spatial extent to which it occurs must be detected. Ideally, this would be accomplished
beforehand via a benchmark spatial survey, which would determine whether the
pattern or process is on a local, regional, or global scale. This is rare in actual field
research, however, due to the lack of time and funding, as well as the ever-changing
nature of such widely-studied organisms such as insects and wildlife.[4] With detailed
information about a species' life-stages, dynamics, demography, movement, behavior,
etc., models of spatial pattern may be developed to estimate and predict events in
unsampled locations.
Landscape Geometry
As defined by Odum and Barrett (2005), landscape geometry is the “study of
the shapes, patterns, and configurations of landscape elements.” The shapes are the
patches of good or acceptable habitat that is surrounded by a matrix of poor or less
favorable habitat. The shape of the patches themselves is a significant characteristic of
the overall landscape geometry (Hamazaki, 1996) Patterns are reflected in the number
and types of patches as well as their distribution throughout the matrix
(configuration). Not specifically identified in this definition is the connectivity
provided by corridors. Corridor characteristics such as width and length contribute to
the overall landscape geometry and can significantly impact the landscapes ecological
functions. Some authors have suggested that corridors can be analyzed as linear
habitat patches rather than landscape separate elements (Hamazaki, 1996 and
Rosenberg and Noon, 1997). Given that landscape heterogeneity is a “central causal
factor” in ecosystem processes (Pickett and Cadenasso, 1995), landscape geometry is
a necessary component in ecosystem research. In addition to the physical parameters
(size, shape, area), landscapes can have functional geometries based upon ecological
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requirements of specific species or species types (e.g. home range). An agricultural
field adjacent to a forested area may be an important patch for certain species
(raptors), but a isolating element for others (amphibians). Based upon the differing
ecological needs of any species, landscape geometry can also be expressed as a
functional geometry that is not directly based upon physical properties of the
landscape itself. Travis and French (2000) state that species dispersal models are
oversimplified. The models need to incorporate more functional than physical
geometric characteristics. Haskell and others (2002) used fractal geometry based on
home ranges to compare resource distribution for different species within the same
landscape.
The concept of landscape sustainability
A sustainable landscape is one that conforms to the environment surrounding it,
requiring only inputs (e.g. water, fertilizer) that are naturally available, with little or
no additional support. It is self-sustaining over long periods of time. It exists in
harmony with its local ecosystem––if bad weather hits, or wildfires or rockslides
devastate your neighborhood, your garden recovers quickly. The landscape is diverse
enough to remain resilient and productive indefinitely.
When evaluating your landscape for sustainability, there are three main areas to
consider: How it responds to the local ecology (ecological), how much it costs to
maintain (economic), and how it affects your family and neighbors (socio-cultural).
1.
Ecological: How well does your design match the local ecology, utilizing
similar plants and mimicking local landforms? You'll want your garden to help
feed, and give shade and housing to local birds and insects, as well as humans.
2.
Economic: How much does it cost to maintain your landscape? You'll want it
to thrive with available, natural resources, instead of having to spend extra on
water or chemicals to be healthy and look good. If you have a landscaper, the
landscape should be easy for them to maintain with well paid, but minimal effort.
3.
Socio-cultural: How does the neighbourhood like the way it enhances or
blends with their yards? Your landscape should reflect what you, your family, and
your neighborhood like best about your local environment.
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Domesticated Landscapes
The term “landscape domestication” has become increasingly visible within
the last decade or so. Some find this use of “domestication” to be inappropriate,
however, as domestication is often associated with Charles Darwin and his theory of
evolution. A glance at a dictionary dispels confusion, as there are no mentions of
evolution or selection or genetics in the definitions. The term comes from the
Latin domesticäre to dwell in a house, to accustom (Harlan 1992). A house is a built
environment and has been part of our experience since people started constructing
their own shelters from the elements. The house in the countryside is surrounded by
a garden, which also has a dump heap, both of which are intimately involved in the
domestication of plants. Hence, there is a strong relationship between landscape
domestication and plant or animal domestication, as pointed out by Rindos (1984),
although he preferred the “developing agroecology” to landscape domestication.
Utilization of Learning
Answer the following questions;
1. What is landscape Ecology?
131
2.
3.
4.
5.
6.
7.
8.
9.
What are the elements of landscape?
How are the biodiversity at the community and landscape levels?
What island biogeography?
What is neutral theory?
What is temporal and spatial scale?
What is landscape geometry?
How is the concept of landscape sustainability?
What is domesticated landscapes?
Supplementary
https://www.youtube.com/watch?v=30l6cTHhjVg
https://www.nature.com
https://en.wikipedia.org
https://dengarden.com
https://link.springer.com
https://link.springer.com
Lesson 2: Major Ecosystem Types and Biomes
Target Outcomes
132
At the end of the lesson, you are expected to:
1.
2.
3.
4.
explain marine ecosystems;
explain freshwater ecosystems;
describe terrestrial biomes ;and
understand human-designed and managed systems.
Abstraction
Marine ecosystems
Marine ecosystems are an important part of the world, because the marine
ecosystems give marine life such as: tiny plankton, fish, crustaceans, invertebrates,
reptiles, marine mammals, sharks, and rays a place to live and survive. It also gives
those marine animals a place to hunt. Many marine life have an important role in the
world such as the tiny plankton because without them the world would build up with
carbon dioxide, the plankton absorbs the carbon dioxide in the air and releases oxygen
back into the air. Without marine ecosystems to protect the tiny plankton, more
species would become extinct. The most important marine ecosystems for marine life
are estuaries and coral reefs. These two marine ecosystems are important because the
estuaries are breeding territories for many marine animals, because it is easy for
young-lings to survive there, since there are no known predators that live in that
region. Coral reefs are important for the marine life, because it provides a shelter for
various amounts of species. Coral reefs also are the most diverse ecosystem in the
whole aquatic system. Without all the marine ecosystems, the marine food web and
the whole ocean would be in danger of continuing in its current state.
The threats that have impacted the marine ecosystems are pollution and
overfishing. Pollution is impacting the marine ecosystems, because as more carbon
dioxide is released into the air more of the ice caps are melting. Therefore, the rising
of ocean levels and the decrease in salinity levels. Are causing problems for the
marine life. If the salinity levels keep dropping the marine life that survives in salt
water will not be able to survive in the fresh water rich waters. Pollution is killing
marine animals not only in the salinity drop, but also they eat or get trapped in
harmful garbage, marine life in the ocean die from swallowing or getting caught on
133
trash every day. Over one million sea birds are killed by pollution every year. Also
three hundred dolphin and porpoise are killed by pollution, by either swallowing trash
or getting tangled in trash and one hundred thousand marine mammals are killed by
ingesting plastics and other pollution substance every year. Pollution is a major
reason why marine ecosystems are being threatened. But, another threat to marine
ecosystems are overfishing. Overfishing is a threat for marine ecosystems because a
decrease in number of a species will affect the marine food web disrupting the whole
ocean. If overfishing causes specie to become extinct in the marine ecosystem then it
will have one of the species in the ocean to become overpopulated. Once one specie
becomes overpopulated then that organism dominates the ocean making other species
to become endangered or extinct. The threats in the marine ecosystems can have an
impact that the system will never repair itself, which will disrupt the world more then
any other ecosystem would. However, the Government stepped in and passed an
amendment that decreases overfishing. This amendment helps the ocean to recover
the decrease of marine animals. The amendment puts a set limit for the marine species
we manage.[7] In 2014, 91 percent of annual limits were nit exceeded and only 9
percent were exceed. There are numinous amount of reason why catch limits are
being exceeded such as: miscount of population, by catch in a fishery, and fishing
rates are higher than estimated. Scientist track these number to manage overfishing so
population does not deplete more.
Freshwater ecosystems
Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They
include lakes, ponds, rivers, streams, springs, bogs,
and wetlands.[1] They
can
be
contrasted with marine ecosystems, which have a larger salt content. Freshwater
habitats can be classified by different factors, including temperature, light penetration,
nutrients, and vegetation.
Freshwater ecosystems can be divided into lentic ecosystems (still water)
and lotic ecosystems (flowing water). Limnology (and its branch freshwater biology)
is a study about freshwater ecosystems.[1] It is a part of hydrobiology. Original
attempts to understand and monitor freshwater ecosystems were spurred on by threats
to human health[2] (ex. Cholera outbreaks due to sewage contamination). Early
monitoring focused on chemical indicators, then bacteria, and finally algae, fungi and
134
protozoa. A new type of monitoring involves quantifying differing groups of
organisms (macro invertebrates, macrophysics and fish) and measuring the stream
conditions associated with them.
Five broad threats to freshwater biodiversity include overexploitation, water
pollution, flow modification, destruction or degradation of habitat, and invasion by
exotic species.[4] Recent extinction trends can be attributed largely to sedimentation,
stream fragmentation, chemical and organic pollutants, dams, and invasive species.
[5]
Common
chemical
stresses
on
freshwater ecosystem
health include
acidification, eutrophication and copper and pesticide contamination.[6] Unpredictable
synergies with climate change greatly complicate the impacts of other stressors that
threaten many marine and freshwater fishes.
Terrestrial biomes
A terrestrial biome is an area of land with a similar climate that includes similar
communities of plants and animals. Different terrestrial biomes are usually defined in
terms of their plants, such as trees, shrubs, and grasses.
Factors such as latitude, humidity, and elevation affect biome type:

Latitude means how far a biome is from the equator. Moving from the poles to
the equator, you will find (in order) Arctic, boreal, temperate, subtropical,
and tropical biomes.

Humidity is the amount of water in the air. Air with a high concentration of
water will be called humid. Moving away from the most humid climate, biomes
will be called semi-humid, semi-arid, or arid (the driest).

Elevation measures how high land is above sea level. It gets colder as you go
higher above sea level, which is why you see snow-capped mountains.
Terrestrial biomes include grasslands, forests, deserts, and tundra. Grasslands are
characterized as lands dominated by grasses rather than large shrubs or trees and
include the savanna and temperate grasslands. Forests are dominated by trees and
other
woody
vegetation
and
are
classified
based
on
their
135
latitude. Forests include tropical, temperate, and boreal forests (taiga). Deserts cover
about one fifth of the Earth’s surface and occur where rainfall is less than 50 cm
(about 20 inches) each year. Tundra is the coldest of all the biomes. The tundra is
characterized for its frost-molded landscapes, extremely low temperatures,
little precipitation, poor nutrients, and short growing seasons. There are two main
types of tundra, Arctic and Alpine tundras. Terrestrial biomes lying within
the Arctic and Antarctic Circles do not have very much plant or animal life.
Utilization of Learning
Answer the following questions;
1. What is a marine ecosystem?
2. What is a freshwater ecosystem?
3. What is terrestrial biome?
Supplementary
https://www.youtube.com/watch?v=A495e31cDdE
https://wiki.seg.org
https://flexbooks.ck12.org
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