A trophic level consists of organisms that get their energy from a similar source. Each step in a food chain is a trophic level. A food chain is a series of organisms each eating or decomposing the preceding organism in the chain. For example, in a lake phytoplankton are eaten by zooplankton and zooplankton are eaten by small fish. A food web is similar to a food chain, but in a food web there are many interconnected and interacting food chains. In a typical food chain, a producer or autotroph is the source of solar energy that powers the ecosystem. For example, in a grazing food web a herbivore eats living plant tissue (the producer) and is eaten in turn by an array of carnivores and omnivores. In contrast, a detrivore harvests energy from dead organic material and provides energy for a separate food chain.

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