ENGG 413 ENVIRONMENTAL SCIENCE AND ENGINEERING
Main Topic 1: Ecological Concepts
EVOLUTION, BIOLOGICAL COMMUNITIES, AND SPECIES INTERACTIONS
Introduction
This lesson includes the discussions about how species diversity is produced through
evolution, how the biological communities are shaped through species interactions and how the
species and populations are affected by community properties. Also, it explains the dynamic and
changing communities.
Learning Outcomes
Intended Learning Outcome 1 (Syllabus)
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Acquire high level of awareness about the environment and its significance.
Topic Outcome
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Describe how evolution produces species diversity
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Discuss how species interactions shape biological communities.
Evolution Produces Species Diversity
We know that each species adapts the environment where it lives. Examples are polar
bears living in sunless, super-cold arctic winter and saguaro cactus surviving the blistering
temperature and dryness of the desert.
Source: aminoapps.com
Adaptation
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One of the most important concepts in biology.
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The acquisition of traits that allow a species to survive in its environment.
2 ways of using the term “Adapt”
1. Acclimation – When an individual organism can respond immediately to a changing
environment.
Example: Keeping a house plant indoors all winter and then put it out in full sunlight
in the spring. The leaves become damaged or the plant may grow new leaves with
thicker cuticles and denser pigments that block the sun’s rays. Although the capacity
to acclimate is inherited, houseplants in each generation must develop their own
protective leaf epidermis.
2. Genetic traits - passed from generation to generation and allow a species to live
more successfully in its environment. This process of adaptation to environment is
explained by the theory of evolution.
➢ Evolution – the basic idea is that species change over generations because
individuals compete for scarce resources.
➢ Natural Selection – the process of better-selected individuals passing their traits
to the next generation.
➢ Mutations – changes to the DNA coding sequence of individuals that occurs
occasionally, and the changed sequences are inherited by offspring.
Limiting Factors of Species
Pressure and influence to fitness of an individual and their offspring are exerted by
factors such as environmental. With this, species have limitations in where they can live. These
limiting factors are:
1. Physiological stress due to inappropriate levels of some critical environmental
factor, such as moisture, light, temperature, pH, or specific nutrients.
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ENGG 413 ENVIRONMENTAL SCIENCE AND ENGINEERING
Main Topic 1: Ecological Concepts
2. Competition with other species
3. Predation, including parasitism and disease
4. Luck.
Critical Factor
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According to the chemist Justus von Liebig (1840), the single factor in shortest supply
relative to demand is the critical factor determining where a species lives.
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Temperature, moisture level, nutrient supply, soil and water chemistry, living space, and
other environmental factors must be at appropriate levels for organisms to persist.
Tolerance Limits
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Ecologist Victor Shelford (1877-1968) expanded Liebig’s principle.
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He stated that each environmental factor has both minimum and maximum levels, called
tolerance limits, beyond which particular species cannot survive or is unable to
reproduce.
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The single factor closest to these survival limits is the critical factor that limits where a
particular organism can live.
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In some species, tolerance limits affect the distribution of young differently than they
affect adults.
Ecological Niche
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Habitat – the place or set of environmental conditions in which a particular organism
lives.
•
Ecological Niche – describes both the role played by a species in a biological community
and the set of environmental factors that determine its distribution.
•
Charles Elton (1900-1991) – British Ecologist who defined the concept of niche in 1927.
According to him, each species had a role in a community of species, and the niche
defined its way of obtaining food, the relationships it had with other species, and the
services it provided to its community.
•
G. E. Hutchinson (1903–1991) – The American limnologist who, thirty years later,
proposed a more biophysical definition of niche. According to him, every species exists
within a range of physical and chemical conditions such as temperature, light levels,
acidity, humidity, or salinity. It also exists within a set of biological interactions such as
predators and prey present, defenses, or nutritional resources available.
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Generalists – species that tolerate a wide range of conditions or exploit a wide range of
resources. Example: Species that thrive in broad variety of environments such as weedy
species or pests (rats, cockroaches, or dandelions).
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Specialists – species that have a narrow ecological niche. Examples are Giant Panda and
Giant Saguaro.
Speciation
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Speciation
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The development of a new species.
o
As a population becomes more adapted to its ecological niche, it may develop
specialized or distinctive traits that eventually differentiate it entirely from its
biological cousins.
2 kinds of speciation:
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ENGG 413 ENVIRONMENTAL SCIENCE AND ENGINEERING
Main Topic 1: Ecological Concepts
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Allopatric Speciation – speciation that occurs when populations are
geographically separated.
*Geographic Isolation – when the habitat are far enough apart that population
were genetically isolated; they couldn’t interbreed with populations on the other
habitat.
o
Sympatric Speciation – speciation that occurs within one geographic area.
*Behavioral Isolation – when two identical species live in similar habitats but have
different mating calls. This difference is enough to prevent interbreeding.
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Directional Selection – the shift toward one extreme of a trait.
Taxonomy
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The study of types of organisms and their relationships.
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With this, organisms can be traced which common ancestors they have descended.
Binomials
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also called Scientific or Latin Name
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Identify and describe species using Latin or Latinized nouns and adjectives, or
names of people or places.
o
Scientists communicate using scientific names instead of common names like
lion, dandelion, or ant to avoid confusion.
Species Interactions
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Competition leads to resource allocation.
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Predation is an important type of selective pressure.
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Symbiosis benefits both species involved.
Competition
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A type of antagonistic relationship within a biological community.
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Organisms compete for resources that are in limited supply such as energy and matter in
usable forms, living space, and specific sites to carry out life’s activities.
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Competition shapes a species population and biological community by causing
individuals and species to shift their focus from one segment of a resource type to
another.
Types of competition:
➢ Intraspecific competition – competition among members of the same species.
➢ Interspecific competition – competition between members of different species.
Predator
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Any organism that feeds directly on another living organism, whether or not this kills the
prey.
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Herbivores, carnivores, and omnivores, which feed on live prey, are predators.
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Predation is a powerful but complex influence on species populations in communities.
Predation affects:
1. All stages in the life cycles of predator and prey species.
2. Many specialized food-obtaining mechanisms.
3. The evolutionary adjustments in behavior and body characteristics that help prey
avoid being eaten and help predators more efficiently catch their prey.
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ENGG 413 ENVIRONMENTAL SCIENCE AND ENGINEERING
Main Topic 1: Ecological Concepts
Source: (McLaughlin, 2020)
Symbiosis
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Two or more species live intimately together, with their fates linked.
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Symbiotic relationships often enhance the survival of one or both partners.
Types of Symbiosis:
❖ Mutualism – type of symbiosis in which both members’ benefits. (e.g. Dogs and
Humans)
❖ Commensalism – type of symbiosis in which one member clearly benefits and the
other apparently is neither benefited nor harmed. (e.g. a spider building a web on
a tree)
❖ Parasitism – a form predation may also be considered symbiosis because of the
dependency of the parasite on its host. (fleas and mosquitoes feed on blood from
other organisms
❖ Endosymbiosis – one species living inside another one. (e.g. Protozoans that live
inside termites and help them digest wood)
❖ Ectosymbiosis – one species living on the surface of the other species. (e.g. Lice
that feed on the skin, blood, or oil secretions of the host)
Keystone Species
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Plays a critical role in a biological community that is out of proportion to its abundance.
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Thought to be the top predators like lions, wolves, and tigers that limited herbivore
abundance and reduced the herbivory of plants.
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Scientists now recognize that less-conspicuous species also play keystone roles.
Community Properties
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Productivity is a measure of biological activity.
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Abundance and diversity measure the number and variety of organisms.
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Resilience and stability make communities resistant to disturbance.
Primary Productivity
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The rate of biomass production.
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An indication of the rate of solar energy conversion to chemical energy.
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ENGG 413 ENVIRONMENTAL SCIENCE AND ENGINEERING
Main Topic 1: Ecological Concepts
Abundance and Diversity
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Abundance is an expression of the total number of organisms in a biological community.
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Diversity is a measure of the number of different species, ecological niches, or genetic
variation present.
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The abundance of a particular species often is inversely related to the total diversity of
the community.
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Communities with a very large number of species often have only a few members of any
given species in a particular area.
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Diversity decreases but abundance within species increases as we go from the equator
toward the poles.
Ecological Structure
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Ecological structure refers to patterns of spatial distribution of individuals and
populations within a community, as well as the relation of a particular community to its
surroundings.
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At the local level, even in a relatively homogeneous environment, individuals in a single
population can be distributed randomly, clumped together, or in highly regular patterns.
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In randomly arranged populations, individuals live wherever resources are available.
Ordered patterns may be determined by the physical environment but are more often
the result of biological competition.
Resilience and Stability
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Many biological communities tend to remain relatively stable and constant over time.
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Robert MacArthur (1955) - a graduate student at Yale, proposed that the more complex
and interconnected a community is, the more stable and resilient it will be in the face of
disturbance.
Three kinds of stability or resiliency in ecosystems:
1. Constancy – lack of fluctuations in composition or functions
2. Inertia - resistance to perturbations
3. Renewal - ability to repair damage after disturbance
Edges and Boundaries
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The boundary between one habitat and its
neighbors is an important aspect of community
structure. These relationships are called edge
effects.
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The edge of a patch of habitat is sometime
relatively sharp and distinct.
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In moving from a woodland patch into a
grassland or cultivated field, you sense a
dramatic change from the cool, dark, quiet
Source: (Cunningham & Cunningham, 2012)
forest interior to the windy, sunny, warmer, open space of the meadow.
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In other cases, one habitat type intergrades very gradually into another, so there is no
distinct border.
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Ecotones are what the ecologists call the boundaries between adjacent communities.
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Closed Community - a community that is sharply divided from its neighbors.
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ENGG 413 ENVIRONMENTAL SCIENCE AND ENGINEERING
Main Topic 1: Ecological Concepts
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Open Community - a community with gradual or indistinct boundaries over which many
species cross.
*Often this distinction is a matter of degree or perception.
Dynamic and Changing Communities
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Some biological communities are dependent on periodic disturbance.
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Introduced species can cause profound community change.
Ecological Succession
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Climax Community is the community that developed last and lasted the longest.
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Ecological Succession is the history of community development. When a succession
occurs, organisms occupy a site and change the environmental conditions.
2
kinds of succession:
1. Primary succession - Land that is bare of soil (a sandbar, mudslide, rock face, and
volcanic flow) is colonized by living organisms where none lived before.
2. Secondary succession - When an existing community is disturbed, a new one
develops from the biological legacy of the old.
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Ecological development or facilitation - In both kinds of succession, when organisms
change the environment by modifying soil, light levels, food supplies, and microclimate,
the change permits new species to colonize and eventually replace the previous species.
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Pioneer species - In primary succession on land, the first colonists (microbes, mosses,
and lichens) that can withstand a harsh environment with few resources.
Source: (Cunningham & Cunningham, 2012)
An example of primary succession, shown in five stages (left to right). Bare rocks are colonized by lichens
and mosses, which trap moisture and build soil for grasses, shrubs, and eventually trees.
Disturbance
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Any force that disrupts the established patterns of species diversity and abundance,
community structure, or community properties.
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Disturbances on earth: landslides, mudslides, hailstorms, earthquakes, hurricanes,
tornadoes, tidal waves, wildfires, and volcanoes.
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ENGG 413 ENVIRONMENTAL SCIENCE AND ENGINEERING
Main Topic 1: Ecological Concepts
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Animals can cause disturbance too.
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Disturbance-adapted species - species that can survive periodic disturbance (survive fires
underground, or resist the flames, and then reseed quickly after fires).
Introduced Species
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Continuous introduction of new community members and the disappearance of
previously existing species are requirements of succession.
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New species move in as conditions become suitable; others die or move out as the
community changes.
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New species can be introduced after a stable community already has become
established. Some of them cannot compete with existing species and fail to become
established. Others are able to fit into and become part of the community, defining new
ecological niches.
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If an introduced species preys upon or competes more successfully with one or more
populations that are native to the community, the entire nature of the community can be
altered.
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