Populations & balance

All animals of the same species in an area are called a population, for example all hares in a meadow. Plants form populations too, such as all the beech trees in a forest. At first a population grows fast, because food and space are plentiful. But no growth goes on forever. At some point the population hits a limit.

The limit of the environment

Every habitat can feed only a certain number of animals. This upper limit is called the environmental carrying capacity, or carrying capacity for short. If there are too many hares, the grass no longer feeds them all. Then fewer young ones find enough food, and the population stops growing. It settles around the carrying capacity.

Predator and prey in interplay

Predator and prey are closely linked. If there are many hares, the foxes find food easily and have more young. Then the number of foxes rises, and they eat so many hares that their number drops. Now the foxes go hungry, their number falls, and the hares recover. So both swing up and down in turn.

Without interference from outside, the numbers usually settle around a rough balance. That balance is never rigid, it is made up of exactly this constant up and down. Humans, however, can disturb it badly, for example by hunting too much, destroying habitat, or bringing in foreign species. Then a population can collapse or grow out of control. Nature conservation tries to keep the swings within a healthy range and to bring disturbed ecosystems back into order.