Keystone Species
A species’ ecological niche defines how it interacts with its environment and other organisms, but some species have an impact far greater than their numbers suggest.
These keystone species play a critical role in maintaining the structure and balance of their communities. By influencing the abundance or behaviour of other species, they help shape the entire ecosystem, showing how individual niches can have expansive effects.
A keystone species is a species whose influence on the structure and function of a community is disproportionately large relative to its abundance or biomass, such that its removal leads to significant changes in species composition, population dynamics and ecosystem processes.
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 and Communities
Keystone species maintain the structure of a community because their actions stabilise interactions among many other species.
They often regulate population sizes by controlling prey or competitor numbers, preventing any single species from becoming overly dominant. Some provide essential resources or create habitat that many organisms rely on, which supports high biodiversity. Others influence physical conditions such as light levels or nutrient availability, shaping which species can survive.
By holding these interactions in balance, keystone species help maintain the overall organisation and functioning of the community.
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.