FOOD
CHAIN
In
ecology, a sequence showing the feeding relationships between organisms in a particular
ecosystem. Each organism depends on the next lowest member of the chain for its
food. A pyramid of numbers can be used to show the reduction in food energy at
each step up the foodchain.Energy in the form of food is shown to be
transferred from autotrophs, or producers, which are principally plants and photosynthetic
microorganisms, to a series of heterotrophs, or consumers. The heterotrophs
comprise the herbivores, which feed on the producers; carnivores, which feed on
the herbivores; and decomposers, which break down the dead bodies and waste
products of all four groups (including their own), ready for recycling. In
reality, however, organisms have varied diets, relying on different kinds of
foods, so that the food chain is an oversimplification.
The
more complex food web shows a greater variety of relationships, but again emphasizes
that energy passes from plants to herbivores to carnivores. Environmentalists
have used the concept of the food chain to show how poisons and other forms of
pollution can pass from one animal to another, threatening rare species. For
example, the pesticide DDT has been found in lethal concentrations in the
bodies of animals at the top of the food chain, such as the golden eagle Aquila
chrysaetos.
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