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E c o l o g y I
Main Idea: the interactions between Organisms and their interactions with the Environment
A. Ecology (Definition) – the study of how organisms interact with the living and nonliving things that surround them.
1. The fundamental concept of ecology is that all living things are dependent on each other and they interact with one another and with the physical environment. surrounds an organism.
B. Parts of an Ecosystem
2. Environment (Definition) – every living and nonliving thing that
1. Ecosystem (Definition) – all the living and nonliving things that interact in a specific area .
I.e. pond, field of corn, fish tank, woodland, ocean or a decaying log.

a. Biotic Factors (Definition)
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– the living parts of the environment.
I.e. bacteria, plants and animals.
b. Abiotic Factors (Definition)
– the nonliving parts of the environment.
I.e. soil, water, physical space and energy.
2. Habitat (Definition) – the
“ home ” of a particular species. i.e. fields, forests, oceans, streams and deserts.
3. Population (Definition) – the individuals of a species that live in the same area. i.e. ants in a single anthill, squirrels in the town of Lancaster, or worms in the courtyard.

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4. Community (Definition) – different populations in a given area combine to form a community.
I.e. all the dogs, cats, people, squirrels, birds (etc.) in the town of
Lancaster.
5. Biosphere (Definition) – all of the earth’s ecosystems
(any portion of the earth, including all of the water, land, and air in which organisms survive.) a. Throughout the biosphere, organisms interact and compete for vital resources, such as food , space , and shelter .
C. Environmental Limits on Population Size
1. The growth and survival of organisms depends on the physical conditions and on the resources available to the organism.
2. If they had unlimited resources
, living things could produce populations of infinite (unlimited) size.
3. Within any ecosystem, however, resources ( oxygen, carbon dioxide,water,

4 nutrients, space, and sunlight ) are finite ( limited ).
4. Because the resources are limited, organisms must compete with one another to survive. a. Competition (Definition) – the struggle for resources among organisms.
b. Within any one species, competition keeps the size of that species’ population balanced. c. Populations tend to increase or decrease depending on the resources that are available at the time. Over long periods of time, however, the size of the population remains stable .
5. Limiting Factors (Definition) – anything that limits the size of a population. a. Limiting factors can be abiotic
( nonliving ) :
1. Abiotic factors, such as the amount of dissolved oxygen in a pond, may limit the kinds and numbers of fish that can live there.

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2. Abiotic factors, such as the amount of sunlight filtering through a forest may limit the number of green plants living on the forest floor.
3. Other limiting factors that are abiotic include the intensity of light , the temperature range in the environment, minerals that are available in the water or soil, or the type of rock or soil in the ecosystem. b. Limiting factors can also be biotic
( living ) :
1. An important biotic factor that limits population sizes is the relationship between predators and prey. a. Predator (Definition) – kill and eat other organisms. b. Prey (Definition) – killed for food.
2. As predators kill and eat their prey, they limit the growth of the prey population.

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3. If too many prey animals are killed, predators begin to starve
, and their population is reduced.
4. With fewer predators, the size of the prey population begins to recover .
6. Carrying Capacity (Definition) – the number of organisms of any single species that an ecosystem can support. a. Carrying Capacity of a species is determined by available energy , water , oxygen , minerals
, and the interactions of its organisms . b. For example, a field’s carrying capacity for a population of foxes is affected not only by the climate
, but also by the number and kinds of other populations present.
1. If there are many mice for the fox population to eat, the fox population may increase drastically.
2. If there are many viruses affecting the foxes, their population may crash .

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3. The population of organisms in a given area will increase until the carrying capacity is reached.
There will be a quiz on this entire packet on
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There will be a TEST on this entire packet on
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Unit XII Ecology Notes [Notes2000 #7]