Causes of endangerment and extinction

A species is endangered when its risk of extinction is high. A species is extinct when no individuals of that species remain anywhere.

A population can sustain itself only if enough individuals survive and reproduce. Pressures that reduce survival or reproduction can cause a population to decline. If all populations of a species disappear, the species becomes extinct.

Pressures that cause populations to decline

Climate change can alter temperatures, rainfall and other conditions. If conditions change faster than organisms can tolerate them or move to a suitable habitat, fewer may survive and reproduce.

Habitat destruction removes the places where organisms live and the resources they need, such as food, shelter or breeding sites. With fewer suitable places and resources, fewer individuals can survive and reproduce.

Hunting and overharvesting remove organisms from a population. If individuals are removed faster than the population can replace them through reproduction, the population declines.

Pollution can harm organisms directly or make their habitat unsuitable. This can reduce their survival or their ability to reproduce.

Introduced species are species brought into an area where they do not naturally occur. They can threaten native organisms by competing with them for resources, preying on them or spreading disease.

These pressures can act together. As populations decline, the risk that the whole species will disappear increases.