In addition to producers and consumers, an ecosystem also accomodates organisms that act as decomposers. Organisms such as bacteria, fungi, and crayfish can all function as decomposers in their ecosystems. 

Decomposers feed on dead organisms, their parts, and their fecal matter. By doing so, they decompose the dead organisms and their parts, releasing the nutrients contained in them into a form that is accessible to the producers of the ecosystem. Therefore, decomposers act as a kind of link between the "end" of the food chain and its "beginning".


A spotted crayfish functions as a decomposer when it eats dead organisms.

Decomposers play a vital role in the nutrient cycle of a well-functioning ecosystem. A producer, such as a cattail, uses its roots to gather nitrogen. This nitrogen is transferred to an organism that uses the cattail as its food source, such as the larva of a caddisfly. The nitrogen is then transferred to an organism that eats the larva, such as a perch. Finally, when the perch dies, the decomposers of the ecosystem recycle the nitrogen contained within the perch's body into a form that can be used by plants and other producers. This process is an example of the nutrient cycle in action.