ECOLOGY
I. ECOLOGY – the branch of biology that deals with the interactions between organisms and the
relationships between organisms and the environment
A. Levels of Ecological Organization:
1. Organism - a given individual of a particular species
2. Population – includes all the members of a species living in a given area at a particular time
ex) perch in the Niagara River; deer in NT
3. Community - all the populations in a given area
ex) all plants and animals in Lake Erie
4. Ecosystem - all the members of a given community plus the non-living factors of the
environment and the interactions between the two
Ex) plants, animals, climate, soil, rocks, etc. in a forest
5. Biosphere – The portion of the earth in which life exists. All the earth’s ecosystems
interacting with one another.
B. Requirements for a Stable Ecosystem
Certain requirements must be met for a stable ecosystem to exist:
1. There must be a constant supply of energy (sunlight for photosynthesis).
2. There must be producers (autotrophs) – organisms that transfer the sun’s energy to organic
compounds (food).
3. There must be a recycling of materials between organisms and the environment.
4. Biodiversity must exist.
Biodiversity – the number of different species in an ecosystem. The more variation within an
ecosystem, the more likely it is to remain stable when the environment changes.
Other Ecology terms:
Terrestrial – land
Aquatic - water
Fauna - animals
Flora - plants
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Factors that Disrupt Ecosystem Stability and Decrease Biodiversity
A stable ecosystem can be altered by the activities of other organisms (including humans), climate changes
or natural disasters. The altered ecosystem can usually recover through gradual changes back to a point of
long term stability.
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climate change
habitat change, loss or destruction
pollution/nutrient loading
invasive species
overhunting/exploitation
B. Limiting Factor - an environmental condition that limits the growth of a population
ex) Availability of food; Availability of shelter; Predation; Temperature; Rainfall
Carrying Capacity - the maximum size of a population that can be sustained in an area over a long
period of time; often determined by food supply
II. COMPONENTS OF AN ECOSYSTEM:
A. Living (Biotic) Factors:
1. Producers - organisms that make their own food; also known as autotrophs
Ex) plants and algae
2. Consumers – (heterotrophs) - organisms that feed on other organisms
a. herbivores - consumers that eat producers Ex) cows, caterpillars, horses, deer
b. carnivores - consumers that eat other animals Ex) lions, spiders, sharks, polar bear
c. omnivores - consumers that eat both plants and animals
Ex) black bear, raccoons
d. scavengers - animals that eat dead and decaying animal matter
Ex) buzzards, vultures, hyenas, crabs
e. decomposers - organisms that break down dead organisms Ex) fungi & bacteria
B. Non-Living (Abiotic) Factors: air, water, rocks, minerals
1. Climate - includes amount of rainfall and sunlight and the temperature range of a region
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III. ECOSYSTEM INTERACTIONS - For an ecosystem to be self-sustaining, there must be a flow of energy
between organisms. The pathway of energy flow through the living components of an ecosystem are
represented by food chains and food webs.
1. Food Chains - the pathway in which energy flows from organism to organism
Producer  Consumer 1  Consumer 2  Consumer 3
Grass  Grasshopper  Frog  Snake  Hawk
2. Energy Pyramids - greatest energy/biomass at bottom (producer) level; diminishes at upper
levels
 Energy is LOST at each level of the pyramid…
1) as HEAT
2) as ATP (energy for metabolism)
3) to make tissues
energy that is LEFT OVER moves to next level
 As ENERGY is lost from one trophic level to the next, less BIOMASS and FEWER
organisms can be supported
Example : there are fewer wolves in a habitat than deer
4. Food Webs - all the complex, interconnected food chains in a community; ecosystems are
more likely to exist as food webs rather than as food chains. In a natural community, most
organisms eat more than one species and may be eaten, in turn, by more than one species.
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B. Relationships Between Organisms in an Ecosystem:
1. Competition
Habitat – the place where an organism lives
1. Different species living in the same habitat, may require the same resources. When the
resources are limited, competition occurs among the species.
2. Competition - is the struggle between different species for the same limited resources. The
more similar the needs of the species, the more intense the competition.
3. Each species occupies a niche in the community.
Niche - the role the species plays, and includes the type of food it eats, where it lives, where it
reproduces, and its relationships with other species.
2. Symbiotic Relationships - relationships with members of other species in which at least one
of the two benefits from the arrangement
a. mutualism – both species benefit; bees & flowers; termites & protozoa; ibises and
rhinoceros / crocodiles
(+,+)
b. commensalism – one organism benefits, one is unaffected; remora & shark;
barnacles & whales (+, 0)
c.parasitism - one organism benefits (parasite), one is harmed (host)
(+,-);fleas & dogs, ticks & humans, tapeworms, lampreys, leeches
3. Predation - one organism kills (predator) and eats another (prey)
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IV. MATERIAL CYCLES - In a self-sustaining ecosystem, various materials are recycled between organisms
and the abiotic environment. The recycling process allows materials to be used over and over again.
A. Water Cycle - Sunlight causes water to evaporate from oceans. Moisture forms clouds which
eventually produce precipitation in the form of rain, snow, sleet, etc. Some precipitation falls back
into the ocean, some falls on land and run into lakes and rivers. Animals or plants can take in this
water for their usage. Some water vapor is added to the atmosphere by aerobic respiration in plants
and animals and by transpiration in plants. All water will eventually return to ocean to begin the
cycle again.
B. Carbon-Oxygen Cycle - The carbon-oxygen cycle involves the processes of respiration and
photosynthesis. In respiration, glucose and oxygen are combined releasing energy and producing CO2
and H2O. In photosynthesis, water and carbon dioxide with the energy from the sun are combined to
produce glucose (containing the energy) and oxygen. Each process compliments the other, and the
ecosystem maintains its balanced communities.
C. Nitrogen Cycle - Nitrogen is needed by all living things because it is part of the structure of amino
acids and proteins. In this cycle, nitrogenous wastes and the remains of dead organisms are converted by
decomposers and soil bacteria into compounds that can be used by autotrophs.
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V. CHANGES IN THE ECOSYSTEM
Succession – the replacement of one kind of community with another is called ecological succession. The
kind of stable ecosystem that develops in a particular geographical area depends on climate.
Climax communities - Succession ends with the development of a climax community in which the
populations of plants and animals exist in balance with each other and the environment. In Western New
York, our climax community would be deciduous trees like oak, maple, beech, and willow.
Deciduous trees – lose their leaves in the fall
B. Pioneer Organisms - the first organisms to populate a barren region. They begin the process of
succession. Ex) lichens
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