Trophic Levels

Species within an ecosystem are organized into a food chain, a sequential order in which energy and nutrients are passed through different organisms. Each species in the chain represents a specific position known as a trophic level.

The lowest end consists of primary producers called autotrophs, organisms that obtain the energy to synthesize new organic matter from an abiotic energy source, such as sunlight.

All of the levels above consist of heterotrophs, which must obtain energy from other organisms. The first level of heterotrophs are primary consumers, organisms that feed directly on primary producers. Next up, secondary consumers obtain energy from feeding on primary consumers, and they are subsequently eaten by tertiary consumers.

However, organisms are not always exclusive to these categories. For example, a hawk can be both a secondary consumer feeding on seed eating birds, or a tertiary consumer feeding on snakes which may also feed on the seed eating birds.

Decomposers, including fungi, bacteria and detritivores, make up the final trophic level. These organisms feed on the dead remains of other organisms, and can be placed anywhere within the food chain.