A keystone species is a species that is crucial or essential to the ecosystem’s community structure. Originally, a keystone species was always thought to be the top predator, such as the gray wolf. Scientists have found that wolf population sizes influence populations of both their prey and other species in the environment. However, a more recent viewpoint recognizes that less conspicuous species are also very important, as all species are interconnected in a biological community. Other examples of keystone species include the sea star Pisaster, found along the coast of Washington state, that feeds on mussels and prevents the mussels from crowding out other species. Another example is the black-tailed prairie dog of the prairie ecosystem—not only is it a critical source of food for larger predators, its burrowing loosens the soil and its burrows act as home for other creatures.