Bio Review Notes

Bio Review Notes #58
COMMUNITY ECOLOGY Performance Objectives:

After completing this lesson, students will be able to:

Describe a community, and the types of species that typify most communities

Explain community succession

Describe food pyramids and biomagnification

A community consists of all the species that live together and interact in a given habitat. Energy moves through community food chains from primary producers to primary consumers to secondary and higher-order consumers, forming a food pyramid with four or fewer trophic levels.

Community: All the species that live together and interact in a given habitat, such as a particular marsh or coral reef.

Biomass: The total quantity of living material in a community.

Food chains: Each community has primary producers (autotrophs) that derive energy from sunlight (or chemicals) and convert CO₂ into organic compounds. Most autotrophs are photosynthetic plants; their rate of synthesis of new biomass is called primary production. Organisms that feed on other species are called heterotrophs.

Primary producers are eaten by primary consumers (herbivores).
Primary consumers are eaten by secondary consumers (carnivores).
Secondary consumers are eaten by higher-order consumers.

Food webs: Many food chains are so intricate that they are called food webs.

Food/energy pyramid: Each trophic level has less energy and biomass than the level that supports it. Ratios between levels reflect the low level of energy conversion. The great energy loss at each level limits the maximum number of levels to about four.

Biomagnification: A chemical that is not easily broken down (like a heavy metal or long-lasting pesticide) reaches higher concentrations as it ascends the food chain, because the amount (largely unchanged) is distributed in a smaller biomass at each level.

Succession and climax: When new habitat becomes available (as after a forest fire or the birth of a new island), the first colonizers form a community, which makes new niches available for new species to come in. Some of the newcomers may force out earlier species. In this process, called succession, communities keep replacing one another. If enough species resist displacement, they form a climax community. In other cases, there is no climax; species turnover continues indefinitely.

Index Syllabus

rev. Aug. 2011