Ecology
PART I
Lesson Objectives
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Describe ecological levels of organization in the biosphere.
Distinguish between abiotic and biotic factors.
Define organism, population, community, ecosystem, biome,
and biosphere as the term are used in ecology and other
ecological concepts.
Identify factors that determine population growth rate.
Compare and contrast exponential and logistic growth.
Define limiting factors and their effect on population
dynamics.
Compare and contrast niches and habitats.
Identify and describe terrestrial biomes.
Give an overview of aquatic biomes.
Describe characteristics of biotic and abiotic components of
aquatic and terrestrial ecosystems
Introduction
Levels of Organization
• Ecologists study organisms and their
environments at different levels of
organization:
– Biosphere: consists of all organisms on Earth
– Biome: group of ecosystems that have the same
climate and dominant communities.
– Ecosystem: consists of living things and their
environment.
– Community: consists of populations of
different species that live in the same area
and interact together.
– Population: organisms of the same species
that live in the same area, interact with one
another, and produce fertile offspring.
– Organisms: are individual living things.
This is the lowest level of organization that
ecologists study. Biologists study organisms,
organ systems, organs, tissues, cells,
organelles, and molecules. Chemists study
atoms and subatomic particles.
Organisms and the Environment
• Organisms: life form consisting of one or
more cells; has characteristics of life.
• Environment includes both living (biotic)
and nonliving things (abiotic).
Biotic and Abiotic Factors
• Biotic living organisms
• Abiotic nonliving or physical factors
• Together determine productivity of the
ecosystem in which organisms’ live
What Is a Population?
In biology, a population is a group of organisms
of the same species that live in the same area.
How large a population is and how fast it is
growing are often used as measures of its
health.
Population Growth Rate
• Population growth rate (r) is how fast a
population changes in size over time. A
positive growth rate means a population is
increasing. A negative growth rate means
it is decreasing. The two main factors
affecting population growth are the birth
rate (b) and death rate (d).
Births and Deaths: Balancing Costs
of Reproduction and Survival
• growth rate = birth rate – death rate
r=b–d
Other Factors Affecting
Population Growth Rate
Population growth may also be affected by
people coming into the population from
somewhere else (immigration, i) or leaving
the population for another area (emigration,
e). The formula for population growth takes
all these factors into account.
• r = (b + i) - (d + e)
r = population growth rate; b = birth rate; i = immigration
rate; d = death rate; and e = emigration rate
Patterns of Population Growth
• At first, exponentially then logistically until
carrying capacity is reached
After 5 hours of exponential growth;
one bacteria yields…
32,768
Limits to Population Growth
• limiting factor is a property of a
population’s environment – living or
nonliving – which controls the process of
population growth. Biologists have
identified two major types of limiting
factors:
– Density-dependent factors
– Density-independent factors.
What Is a Community?
Communities are made up of populations of
different species. A community is the biotic part
of an ecosystem. It consists of all the
populations of all the species in the same area.
It also includes their interactions.
What Is an Ecosystem?
An ecosystem is a unit of nature and the focus
of study in ecology. It consists of all the biotic
and abiotic factors in an area and their
interactions. Ecosystems can vary in size.
A lake could be considered an ecosystem. So
could a dead log on a forest floor. Both the lake
and log contain a variety of species that interact
with each other and with abiotic factors.
Ecosystem Components
• Niches
• Habitats
• Competitive Exclusion Principle
The Niche
Niche organism’s occupation (role), where it
lives, and way in which organism’s use
conditions they exist in
– Food it eats
– Place in food web
– How it gets food
– Range of temperatures
needed for survival
– When and how it
reproduces
The Habitat
• Physical environment to which an
organisms has become adapted and
survives in.
Competitive Exclusion Principle
• Two different species
cannot occupy the
same niche in the
same geographic area.
If they do they will compete
with one another for the
same food and other resources.
Eventually, one species will
out compete the other.
What Are Biomes?
A biome is a group of similar ecosystems
with the same general abiotic factors and
primary producers. Biomes may be
terrestrial or aquatic.
Terrestrial Biomes
Terrestrial biomes include all the land areas
on Earth where organisms live. The
distinguishing features of terrestrial biomes
are determined mainly by climate (abiotic
factor). Terrestrial biomes include tundras,
temperate forests and grasslands,
chaparral, temperate and tropical deserts,
and tropical forests and grasslands.
Terrestrial Biomes and
Climate
• Climate is the average weather in an area over a
long period of time. Weather refers to the
conditions of the atmosphere from day to day.
• In terms of moisture, climates can be classified
as arid (dry), semi-arid, humid (wet), or semihumid. The amount of moisture depends on both
precipitation and evaporation.
• Biomes are categorized based upon their
climate types.
Climate and Biodiversity
Climate determines plant growth, it also
influences the number and variety of other
organisms in a terrestrial biome. Biodiversity
generally increases from the poles to the
equator. It is also usually greater in more
humid climates.
Climate and Adaptations
Organisms evolve adaptations that help them survive in the
climate of the biome where they live. For example, in biomes
with arid climates, plants may have special tissues for storing
water. The desert animals also have adaptations for a dry
climate. In biomes with cold climates, plants may adapt by
becoming dormant during the coldest part of the year.
Dormancy is a state in which a plant slows down cellular
activities and may shed its leaves. Animals also adapt to cold
temperatures. One way is with insulation in the form of fur and
fat.
Survey of Terrestrial Biomes
Terrestrial biomes are classified by climatic factors
and types of primary producers.
Aquatic Biomes
Terrestrial organisms are generally limited by temperature
and moisture.
Therefore, terrestrial biomes are defined in terms of these
abiotic factors.
Most aquatic organisms do not have to deal with extremes
of temperature or moisture.
Instead, their main limiting factors are the
availability of sunlight and the
concentration of dissolved oxygen
and nutrients in the water.
Aquatic Biomes and Sunlight
In large bodies of standing water, including the ocean and lakes, the water
can be divided into zones based on the amount of sunlight it receives:
1. The photic zone extends to a maximum depth of 200 meters; enough
sunlight penetrates for algae and other photosynthetic organisms to
photosynthesize.
2. The aphotic zone is water deeper than 200 meters; too little sunlight
penetrates for photosynthesis to occur. As a result, food must be made by
chemosynthesis or else drift down from the water above.
Aquatic Organisms
Aquatic organisms generally fall into three broad groups: plankton, nekton, and
benthos. They vary in how they move and where they live.
1. Plankton are tiny aquatic organisms that cannot move on their own. They live in
the photic zone. They include phytoplankton and zooplankton. Phytoplankton are
bacteria and algae that use sunlight to make food. Zooplankton are tiny animals that
feed on phytoplankton.
2. Nekton are aquatic animals that can move on their own by ‘‘swimming” through the
water. They may live in the photic or aphotic zone. They feed on plankton or other
nekton. Examples of nekton include fish and shrimp.
3. Benthos are aquatic organisms that crawl in sediments at the bottom of a body of
water. Many are decomposers. Benthos include sponges, clams, and anglerfish
which are adapted to a life in the dark.
What Is the Biosphere?
The biosphere is the global sum of all ecosystems; integrating
all living beings and their relationships, including their
interactions with the elements of the lithosphere, hydrosphere,
and atmosphere.
Lesson Summary
Ecology is the study of how living things interact with each other and with their environment. The
environment includes abiotic (nonliving) and biotic (living) factors.
• Organisms are dependent upon their environments for energy and matter.
• Population growth rate is how fast a population changes in size over time. It is determined by
rates of birth, death, immigration, and emigration.
• Under ideal conditions, populations can grow exponentially. The growth rate increases as the
population gets larger. Most populations do not live under ideal conditions and grow logistically
instead. Density-dependent factors slow population growth as population size nears the carrying
capacity.
• A community is the biotic part of an ecosystem. It consists of all the populations of all the species
that live in the same area. It also includes their interactions.
• An ecosystem consists of all the biotic and abiotic factors in an area and their interactions. A niche
refers to the role of a species in its ecosystem. A habitat is the physical environment in which a
species lives and to which it is adapted. Two different species cannot occupy the same niche in the
same place for very long.
• Terrestrial biomes are determined mainly by climate. Climate influences plant growth, biodiversity,
and adaptations of land organisms. Terrestrial biomes include tundras, temperate forests and
grasslands, chaparral, temperate and tropical deserts, and tropical forests and grasslands.
• Aquatic biomes are determined mainly by sunlight and concentrations of dissolved oxygen and
nutrients in the water. Aquatic organisms are plankton, nekton, or benthos.
• The biosphere is composed of all the ecosystems on Earth.