When experts decided to reintroduced a small pack of wolves into Yellowstone National Park for the first in 70 years, they never expected such a tremendous change in such a short period of time. They knew wolves would be able to effect the ecosystem of the park, that was what they were after, but they never imagined such a drastic change.
Due to the absence of wolves, one of the primary predators of Yellowstone national park, the herbivorous animals like deer and elks had taken over the park. Their number started to increase drastically and grazed everything around, which eventually left the grounds barren, effected the trees and other small creature on the park. However, after the return of the wolves, even though they were small, they hunted on deer and elks and reduced their number. And the park started to regenerate itself.