Keystone Species
Keystone species: A plant or animal that plays a unique and crucial role in the way an ecosystem functions.
Remove the keystone and the whole arch fails. This is like the keystone species: take that away and the ecosystem is hugely impacted.
Keystone species are those that are known to have an influence on an ecosystem that is disproportionate to their abundance. You are expected to be able to analyse data (from an Australian ecosystem) to identify a keystone species and predict the outcomes of removing the species from an ecosystem.
Sea otters are keystone species that feed on sea urchins. When sea otters are present, sea urchins are limited to small individuals, confined to crevices and deeper areas. This means that kelp forests are allowed to grow the sea urchin population is controlled by sea otters. Kelp-associated species therefore occur in greater abundance due to the increased secondary production and structure provided by the kelp- forest habitat. They also provide important nursery areas for juvenile fish, which may positively influence the abundance of larger fish. Smaller fish species may also use the kelp for spawning and larger, predatory species such as marine mammals and birds are more abundant due to the increased productivity associated with kelp forests.
When sea otters are removed, sea urchin numbers increase and kelp forests are either completely absent, or very limited in size. This has knock on effects for the rest of the ecosystem.