Keystone Species

 A keystone species is an organism that helps define an entire ecosystem. Without its keystone species, the ecosystem would be dramatically different or cease to exist altogether. 

Keystone species have low functional redundancy. This means that if the species were to disappear from the ecosystem, no other species would be able to fill its ecological niche. The ecosystem would be forced to radically change, allowing new and possibly invasive species to populate the habitat. Any organism, from plants to fungi, may be a keystone species; they are not always the largest or most abundant species in an ecosystem. However, almost all examples of keystone species are animals that have a huge influence on food webs. The way these animals influence food webs varies from habitat to habitat. 

Their consumption of plants helps control the physical and biological aspects of an ecosystem.

In African savannas such as the Serengeti plains in Tanzania, elephants are a keystone species. Elephants eat shrubs and small trees, such as acacia, that grow on the savanna. Even if an acacia tree grows to a height of a meter or more, elephants are able to knock it over and uproot it. This feeding behavior keeps the savanna a grassland and not a forest or woodland.  

With elephants to control the tree population, grasses thrive and sustain grazing animals such as antelopes, wildebeests, and zebras. Smaller animals such as mice and shrews are able to burrow in the warm, dry soil of a savanna. Predators such as lions and hyenas depend on the savanna for prey.

Gray wolves are a top predator whose presence has a ripple effect on the rest of its ecosystem. Studies show that wolves keep elk populations in check, preventing them from over-browsing on willow and aspen, which in turn helps maintain healthy stands of trees in the landscape. Wolves are a boon to other predator populations as well, with their uneaten food scraps strengthening the food supply of scavengers like eagles, coyotes, and bears.The gray wolf inhabits just a fraction of its historical range in the lower 48 states, and it remains an endangered keystone species.