This story is a remarkable example of how Mother Nature is always at work to keep things in balance.
In 1995 wolves were reintroduced into the Yellowstone National Park, which had been wolf-free for over 70 years.
Of course, wolves kill a number of different species of animals, but we are certainly less aware that they give life to many others.
What really surprised naturalists and biologist, hovewer, was how the wolfes ended up changing the behavior of the rivers, in the better.
The rivers changed in response to the wolves. The wolves helped regenerating forests and this helped keep the rivers in good shape and preserve biodiversity.
Still skeptical? Just take a look at this: