Question

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.
Which of these species is a keystone species?

Answer 1

In this scenario, the wolves can be considered a keystone species. The reintroduction of the wolves caused a chain reaction that influenced the populations of other species in the ecosystem. The presence of wolves helped regulate the elk population, leading to a cascade of effects on other species within the ecosystem.