Wolves, once native to Yellowstone National Park, were hunted to the point of complete extinction in the park. As a result, the elk population in the park flourished, putting extra demands on the carrying capacity of the park. Many other species, such as certain trees and beavers, were negatively affected by the increase in elk. Years later, wolves were reintroduced into the park. While the elk population decreased after the wolves returned the beaver and songbird populations began to increase as did the populations of various plant species. Which of the following best explains how wolves are a keystone species in this ecosystem? A. Wolves help balance the population sizes of other species, allowing more species to thrive in the wolves presence than in their absence.
B. Wolves prey on certain species, increasing competition among other species, which results in a decrease in biodiversity in the ecosystem.
C. Wolves are not affected by factors that typically limit the population size; therefore, their population can grow exponentially, increasing the demand on the parks' resources.
D. Wolves prey on other species without having any natural predators themselves; therefore, their presence significantly decreases many populations within the community