Question

the gray wolf is a whose removal resulted in in the elk population, which in turn resulted in in the aspen population. once wolves were reintroduced, the elk population but the wolves also changed elk behavior, resulting in that kept the elk out of areas where they could be seen by wolves. camouflage an increase a fear effect grew a decrease declined producer keystone species

Explanation:

A keystone species has a large impact on its ecosystem. When gray wolves (a keystone species) were removed, elk (their prey) had less predation pressure, so elk population increased. More elk meant more feeding on aspen (elk's food source), leading to a decrease in aspen population. When wolves were reintroduced, elk population declined (due to predation). Also, wolves' presence caused a fear effect in elk, changing their behavior to avoid areas where they could be seen (and thus more likely to be preyed upon).

Answer:

keystone species, an increase, a decrease, declined, a fear effect