Wolves

When in 1995 fourteen wolves were set free in Yellowstone National Park, scientists did not even suspect that this would drastically change the entire ecosystem of the park.
There were no wolves in the park for 70 years and all this time deer reigned there, which over the years of uncontrolled reproduction (all the efforts of people to control their population did not bring success) caused great damage to the local flora. Fourteen wolves, of course, could not eat all the deer, but they made them more cautious to choose places for pastures and avoid some parts of the park. Vegetation began to revive in those places. In six years, the number of trees has increased fivefold. There were beavers who need trees to build dams. Muskrats, ducks and fish are brought into the backwaters. The wolves reduced the jackal population, which led to an increase in the number of hares and mice, and they attracted to the park hawks, ferrets and foxes. Bears came to the park, as they were able to drive the wolves away from their prey or eat up their leftovers. The number of berries in the park has increased.

But the most amazing thing is that wolves have changed the course of the rivers. Their beds straightened and stabilized, the erosion of the coast decreased. This happened because the influence of wolves on deer led to the explosive growth of trees and grass along the banks of the rivers, which led to their strengthening. The geography of the park itself has changed, and all thanks to fourteen wolves released there less than twenty years ago.