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?

(1 point)

bears

elk

willows

wolves

Answer 1

wolves

Wolves are the keystone species because their presence has a disproportionate effect on the ecosystem (controlling elk numbers and triggering the trophic cascade that benefited willows, beavers, and other species).