During the 1980s, wolves were reintroduced to Yellowstone National Park after decades of absence due to attempted extermination in the early part of the 20th century. Within 20 years, not only had the wolf population increased, but there was also a dramatic increase in other species, such as aspen, cottonwood, and willow trees, beavers, warblers, insects, and fish. These changes in Yellowstone Park are examples of how important a(n) ________ can be to an ecosystem.

Keystone species are such species that had a large effect on the natural environment. Such species are very important species as they play key role in determining and maintaining the the structure of an ecosystem and also decide or fix which type of species will be there in that environment and what will be the number of those species in that particular community. Without these keystone species an ecosystem could completely cease or all species could not work in that same manner all-together. Wolf is one of an important keystone species in the ecosystem.