wolves were reintroduced to Yellowstone National Park in 1995. they began to hunt the abundant elk population, so elk numbers decreased. The elk carcasses provided food for other predators, like foxes, coyotes, and bears, so all of their populations increased. Elk used to overgraze on willow plants; now that willows are growing back, beaver numbers are increasing, because they prefer the slow-moving water that willows cause.

In the context of the information provided, the wolves are the keystone species. Keystone species are those that have a disproportionately large impact on their environment relative to their abundance. Wolves, by preying on elk, regulate their population and indirectly contribute to the health of the ecosystem. This, in turn, affects other species and plant life, such as the willows, which then support other species like beavers.

Yes, I am confident that wolves are considered the keystone species in this context. The reintroduction of wolves to Yellowstone National Park had significant ecological effects, mainly by controlling the elk population. This control helped to restore vegetation, such as willows, which had been overgrazed by elk. The growth of willows then supported a variety of other species in the ecosystem. The concept of a keystone species is based on the idea that their presence and role are crucial in maintaining the structure and health of the ecosystem. In this case, the wolves play that pivotal role.