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Food Chain/Web

Current Research

Currently there is much debate over what forces control the structure of food webs. Some ecologists believe that food webs are controlled by bottom-up forces referring to the strong connection between primary production and the subsequent production of consumers. For example, adding large amounts of nutrients like phosphorus causes rapid growth of phytoplankton, the primary producers in lakes which subsequently influences consumers in the food web. Other ecologists believe that food webs are controlled by top-down forces meaning the predators near or at the top of the food web. For example, in the Pacific Ocean researchers have found that when sea otters disappear from an area, sea urchin (the favorite food of seaotters) populations increase, and these invertebrates dramatically overgraze down the kelp beds. Removing top predators causes changes all the way down to the primary producers. Carpenter and Kitchell have called this type of control the trophic cascade because such food webs are controlled by forces that cascade down from the top trophic level. Understanding the roles of top-down and bottom-up forces within food webs will allow more effective management of ecosystems.

Resources

Books

Begon, M., J.L. Harper, and C. R. Townsend. Ecology: Individuals, Populations and Communities. 2nd ed. Boston: Blackwell Scientific Publications, 1990.

Bradbury, I. The Biosphere. New York: Belhaven Press, Pinter Publishers, 1991.

Colborn, T.E., et al. Great Lakes: Great Legacy? Baltimore: The Conservation Foundation and the Institute for Research on Public Policy, 1990.

Miller, G.T., Jr. Environmental Science: Sustaining the Earth. 3rd ed. Belmont, CA: Wadsworth Publishing Company, 1991.

Pimm, S.L. Food Webs. New York: Chapman and Hall, 1982.

Jennifer LeBlanc

KEY TERMS

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Bioaccumulation: —The tendency of substances, like PCBs and other hydrophobic compounds, to build in the fatty tissues of organisms.
Biomagnification: —Tendency of organisms to accumulate certain chemicals to a concentration larger than that occurring in their inorganic, nonliving environment, such as soil or water, or in the case of animals, larger than in their food.
Food chain: —A sequence of organisms directly dependent on one another for food.
Food web: —The feeding relationships within an ecological community, including the interactions of plants, herbivores, predators, and scavengers; an interconnection of many food chains.
Hydrophobic compounds: —"Water-hating" chemical substances, such as PCBs and DDT, that do not dissolve in water and become concentrated in the fatty tissues of organisms.
Photosynthesis: —The conversion of radiant energy into chemical energy that is stored in the tissues of primary producers (e.g., green plants).
Primary consumer: —An organism that eats primary producers.
Primary producer: —An organism that photosynthesizes.
Trophic level: —A feeding level in a food web.

Additional topics

Science EncyclopediaScience & Philosophy: Ferroelectric materials to Form and matterFood Chain/Web - History Of Food Web Research, Structure Of Food Webs, Contaminants In Food Webs, Bioaccumulation