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Example of a food web
A food chain, or more correctly, a food web, describes the food and feeding relationships between species in a biotic community. As usually diagrammed, an organism "lower" in a food chain is a source of food energy and material for an organism at a next "higher" level, indicated by an arrow representing biomass transfer. In another words, the food chain or food web shows the transfer of material and energy from one species to another within an ecosystem.
Here is an example of a food chain:
algae → copepod → fish → squid → seal → orca
This "chain" can be described as follows: Killer whales (Orca) feed upon seals, that feed upon squid, that eat small fish, that feed on copepods, that feed on algae. Food chains must begin with an autotroph: a species that has the ability to produce complex organic substances (essentially "food") from an energy source and inorganic materials. In this example, algae—autotrophs by virtue of their ability to photosynthesize—are the base of the food chain.
The term "food web" is distinguished from "food chain" by the fact that such direct steps as shown in the food chain example above seldom reflect reality. Food sources of most species in an ecosystem are much more diverse, resulting in a complex web of relationships as shown in the figure on the right. In this figure, the grouping of Phytoplankton → Herbivorous zooplankton → Carnivorous zooplankton → Arctic char → Capelin on the far right is a food chain; the whole complex network is a food web.
Last updated: 06-02-2005 13:21:43