Ecological niche

An ecological niche is the particular way a species fits into its environment: the range of physical conditions it can tolerate, such as temperature or moisture, the food and other resources it uses, when and where it is active, and how it interacts with predators, prey, competitors and partners. A habitat is where an organism lives; its niche is closer to its role or way of life there. Specialists such as koalas, which eat almost only eucalyptus leaves, have narrow niches, while generalists such as raccoons have broad ones.

The idea was shaped in the early 20th century by Joseph Grinnell, who stressed environmental conditions, and Charles Elton, who stressed feeding relationships. In the late 1950s G. Evelyn Hutchinson combined these views and distinguished the fundamental niche, the full set of conditions a species could occupy on its own, from the realized niche, the usually smaller part it actually occupies once competitors, predators and limited dispersal are taken into account.

Under the competitive exclusion principle, two species cannot share exactly the same niche in one place for long, because one will outcompete the other. Species often avoid this by dividing resources, for example by feeding at different times or heights.