An ecological niche describes the range of resources, environmental conditions and interactions that allow a population to survive and reproduce.

A niche is not simply the place where an organism lives. Habitat describes where an organism occurs; niche describes how it lives there and what conditions and resources its population requires.

A niche can include many dimensions, such as temperature range, moisture, food type, nesting sites, activity time and vulnerability to competitors or predators.

The fundamental niche is the range of conditions under which a species could persist in the absence of limiting interactions with other species. The realized niche is the portion actually occupied when competition, predation, mutualisms and other interactions are present.

Example

A barnacle species may tolerate both upper and lower parts of a rocky shore physiologically. If another species outcompetes it in the lower zone, its fundamental niche includes both zones but its realized niche is restricted mainly to the upper zone.

Niches matter because coexistence depends on how strongly species overlap in their use of limiting resources. Two species can share a habitat while occupying different niches—for example by feeding at different heights, at different times, or on different prey.

The niche concept therefore links organismal requirements to population distribution and species interactions.