Wolves are considered a keystone species in Yellowstone National Park because their presence triggers a chain reaction of ecological changes that benefit the entire ecosystem. Before wolves were reintroduced to Yellowstone in 1995, large herbivores, such as elk, were overpopulated which led to the overgrazing of vegetation causing desertification of large areas. When wolves began to hunt elk, the elk population declined, allowing vegetation to recover, which in turn led to other species such as birds and beavers to thrive. By reducing the elk population, wolves also impacted the behavior of the remaining elk, causing them to avoid specific areas, which allowed riparian areas to recover and created habitat for fish, amphibians, and other wildlife. Thus, wolves not only control the elk population but also help to restore the balance of the ecosystem in Yellowstone National Park.
