Food chains & webs

Grass is eaten by the hare, the hare by the fox. Such a sequence is called a food chain. It shows who eats whom. At the start there is almost always a plant, because plants and algae can make their own food out of sunlight. From the plants the energy travels on step by step to the animals, which all have to eat.

Feeding levels

Each step in the chain is called a trophic level. The plant is the first level, the plant eater the second, the meat eater the third. Some chains have a fourth level with a top predator right at the top. In nature many chains are woven together. Then we speak of a food web.

Why there are only few top predators

At every step most of the energy is lost. A hare uses it for breathing, moving and keeping warm, and in the end it escapes as heat. Only a small remainder ends up in its body and can be passed on. As a rule of thumb we count on about one tenth. That is why a fox needs many hares, and the hares need even more grass. Because so little energy arrives at the top, there are always only few top predators.

Because everything is connected, a disturbance affects the whole web. If the grass disappears, the hares starve, and then the fox has no prey. If the fox is gone, the hares multiply strongly and eat the grass bare. A food web reacts to every change. At the end of the chain nothing is lost: dead plants and animals end up with the decomposers. Fungi and bacteria break them down and return their nutrients to the soil, where new plants use them again.