An example of a keystone species is the sea otter. Sea otters feed on sea urchins, which are herbivores that graze on kelp forests. If sea otters were removed or died out, sea urchin populations would increase and overgraze on kelp forests, leading to the destruction of the ecosystem and the decline of other species that depend on kelp for food and habitat, such as fish and sea birds. This phenomenon is often referred to as a trophic cascade.
