Keystone species help maintain the structure and functioning of an ecosystem. This is because compared to other species in a given habitat, their numbers are greater. Keystone species also determine the numbers and types of other species in an ecosystem.
A decline in the keystone species' numbers could subsequently result in the decline or extinction of other species in the habitat. New species could spring up and force out the indigenous species.
Predators are keystone species, as they control the populations of certain other species. For example, the presence of a lion or leopard can control the population of the antelope species in the ecosystem. If the predator disappears, the antelope population may increase tremendously, and as a result, the ecosystem may not be able to support it. The antelope would begin competing with each other for water and food.
Some herbivores are also keystone species. For example, savannas such as the Maasai Mara plains in Kenya remain a grassland and do not revert to woodland because elephants feed on small trees. As a result, the grasses flourish and animals such as zebras and antelopes that feed on the grasses survive. Carnivores such as leopards, lions and hyenas rely on the savanna for prey.