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)
Responses

willows
willows

bears
bears

wolves
wolves

elk

Answer 1

wolves

Explanation: Wolves have a disproportionately large effect on the ecosystem by controlling elk numbers and triggering a trophic cascade that benefits multiple other species (willows, beavers, foxes, bears).