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Pertaining to living organisms.

Carrying capacity
A maximum number of individuals or maximum population density that a habitat can support.

All the organisms that live within a given area.

An organism that obtains food from other living organisms.

Ecological succession
Changes in the species composition of an ecosystem following a disturbance.

The study of how organisms interact with their environments.

All the organisms that live within a given area and all the abiotic features of their environment.

Exponential growth
A model of population growth in which a population grows at a rate proportional to its size.

Life history strategy
The position a population of organisms occupies on the continuum between producing a large number of “inexpensive” offspring and a small number of “expensive” offspring.

Logistic growth
A model of population growth in which growth slows as the population approaches the carrying capacity of its habitat.

The total set of biotic and abiotic resources a species uses within a community.

A group of individuals of a single species that occupies a given area.

An organism that makes organic molecules from inorganic materials and energy.

A situation in which individuals of two species live in close association with one another.

Trophic level
One of the feeding levels in a food chain, including producers, primary consumers, secondary consumers, tertiary consumers, and so forth.

Review Questions
21.1 Organisms and Their Environment
What is ecology?
Does an organism’s environment include only nonliving components? yes 3.
What is the difference between a community and an ecosystem?
The difference between a community and an ecosystem is one (community) is an area where organisms live and the other (ecosystem) is all the organisms that live within a given area and all the abiotic features of their environment

21.2 Species Interactions
A diagram of who eats what within a community is called a__.
What organisms are at the base of a food chain or food web?
What role do decomposers play? What organisms function as decomposers in most communities?
Can two species have the same niche in a community? Why or why not?
What is parasitism? What are some examples of parasitism?
What is the difference between commensalism and mutualism?
21.3 Energy Flow in Ecosystems
All organisms need energy in order to grow, reproduce, and perform the activities necessary for survival. Where does this energy come from ultimately?
How does sunlight energy enter the biotic world?
How much of the energy at one trophic level becomes available to the next trophic level, on average? What happens to the rest?
What is an energy pyramid?
21.4 Kinds of Ecosystems
What are some of the factors that determine the types of organisms that live in a certain habitat?
What is the primary variable used to classify habitats into major biomes?
Give an example of a biome where the soil is nutrient-poor, and of one where soil is nutrient-rich.
Why are fires essential to savanna habitats?
What are some features of plants found in desert habitats?
What are the three life zones found in aquatic lake habitats?
What’s the difference between plankton and nekton?
What is the intertidal zone, and what are some of the organisms that live there?
21.5 Change in an Ecosystem
What is the difference between primary and secondary succession?
Why are the later colonizers of a habitat dependent on earlier waves of colonizers?
What happens to the total biomass in an ecosystem during succession?
What trend is there in the number of species present in an ecosystem?
Why does regular disturbance sometimes contribute to the biodiversity of a habitat?
21.6 Population Studies
Under what conditions do organisms experience exponential growth?
Why do populations that occupy unpredictable environments often grow exponentially?
Under what conditions does logistic growth resemble exponential growth? When do the two differ?
What is the difference between r-selected and K-selected organisms?
Describe Type I, Type II, and Type III survivorship.
Why is an r-selected life history associated with unstable environments? Why is a K-selected life history associated with stable environments?

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