7.11 Extinction

The loss of species

Extinction is the permanent loss of a species. A steady, low rate of loss is background extinction. A mass extinction is a rapid loss of many species at once — Earth has had five major ones. Causes include rapid environmental change, competition, disease, and catastrophes.

Aftermath and today

Extinction opens ecological niches, which surviving groups can fill through adaptive radiation (rapid diversification). Today, human activity — habitat destruction, climate change, pollution — is driving extinction rates far above the natural background level.

Key terms

Extinction

The permanent loss of a species.

Background extinction

The steady, low natural rate of species loss over time.

Mass extinction

A rapid loss of many species at once; Earth has had five major ones.

Causes of extinction

Rapid environmental change, competition, disease, catastrophes, and human impact.

Adaptive radiation

Rapid diversification of a group into newly opened niches (often after mass extinction).

Try an AP-style question

After a mass extinction, surviving lineages often diversify rapidly. What best explains this?

1. Mutation rates increase to replace lost species
2. Extinction events create new genes directly
3. Vacant ecological niches become available to the survivors
4. The survivors are all identical and cannot compete