Prairie dogs are a keystone species, a species whose very presence contributes to the existence of the ecosystem in which it lives. Prairie dogs contribute to the soil and water quality in their plains ecosystem. Their foraging retains water in the soil and forces fresh new grasses to continually grow. Young grasses have more nutrients for species such as bison and elk.
Elephants are keystone species on African grasslands, known as savannas. Without the presence of elephants, grasslands would probably develop into forests. Elephants graze on trees such as acacias, above, preventing them from growing to maturity.
Sea otters, like this mother and pup, are one of the most important keystone species in the kelp forest habitat. Kelp, a giant species of seaweed, is home to hundreds of species, from sea stars to sharks. Sea urchins eat kelp. Sea otters eat sea urchins, preventing an overpopulation of urchins from destroying the ecosystem.
Some species of hummingbirds are keystone species in the Sonoran Desert. Hummingbirds pollinate many varieties of native cactus and other plants. In areas of the Sonoran Desert with few hummingbirds, invasive species such as buffelgrass have taken over the ecosystem.
Keystone species are often predators, like this mountain lion in Glacier National Park, Wyoming. The deer, rabbits, and bird species in the ecosystem are at least partly controlled by the presence of the mountain lion. Their feeding behavior, or where they choose to make their nests and burrows, is largely a reaction to the mountain lion’s activity.
Sea stars like this one are an important keystone species in tide pools. In fact, the concept of "keystone species" was developed by Dr. Robert Paine, who studied sea stars in their native environment in Makah Bay, Washington. Sea stars eat sea urchins, mussels, and other shellfish that have no other natural predators.