A keystone species is a species that has a massive affect on the ecological community. These species are not usually large in terms of the number of members in the population, but they have a major impact on how the community is shaped. For instance, the sea otter is an example of a keystone species. The sea otters feed on sea urchins, and sea urchins feed on kelp. When sea otters are present, there is a limited number of sea urchins, and kelp forests thrive; however, without sea otters, sea urchins destroy kelp forests and every organism that lives in them. Pictured is an elephant. Elephants are keystone species in the African savanna. Since they are herbivores, they are constantly destroying trees to use as a food source. This results in the abundance of grassland species in the African savanna. If large herbivores (like the elephants) were not present, there would be a proliferation of trees in the savanna, turning it into a low-density forest.