In ecology, a niche is a term describing the relational position of a species or population in an ecosystem.

More formally, the niche includes how a population responds to the abundance of its resources and enemies (e.g., by growing when resources are abundant, and predators, parasites, and pathogens are scarce) and how it affects those same factors (e.g., by reducing the abundance of resources through consumption and contributing to the population growth of enemies by falling prey to them).

Gause's competitive exclusion principle says that those species having identical requirements cannot occupy the same niche indefinitely.