The food chain: who eats who in 

The food chain describes who eats whom in the wild. Every living thing — from one-celled algae to giant blue whales — needs food to survive. Each food chain is a possible pathway that energy and nutrients can follow through the ecosystem.

For example, grass produces its own food from sunlight. A rabbit eats the grass, then a fox eats the rabbit. When the fox dies, bacteria break down its body, returning it to the soil where it provides nutrients for plants, like grass.

Of course, many different animals eat grass, and rabbits can eat other plants besides grass. Foxes, in turn, can eat many types of animals and plants. Each of these living things can be a part of multiple food chains. All of the interconnected and overlapping food chains in an ecosystem make up a food web.

Organisms in food chains are grouped into categories called trophic levels. Roughly speaking, these levels are divided into producers (first trophic level), consumers (second, third and fourth trophic levels) and decomposers.