Wolves are one of the most powerful predators in the world.

Wolves help control the ecosystem and keep it in balance, even more so than you might think.

How, you may ask?

Wolves eat mainly large herbivores, like deer, moose, and elk.  

When wolves were hunted nearly to the brink of extinction in Yellowstone in the mid-1920s, the populations of deer, moose, and elk multiple greatly.  As a result, they overgrazed the land.  Because of their overgrazing, birds could not build trees that beavers could not cut down to build dams.

Because beavers could not create dams, local populations of fish dwindled, which meant less food for their predators like bears.  

In 1974, wolves were officially declared an endangered species and became protected under the Endangered Species Act.  However, it wasn't until the 1990s when population recovery efforts began to take place.

Once 31 gray wolves from Canada were captured and brought to Yellowstone, things drastically changed for the better.  The populations of deer, moose, and elk dwindled greatly.  These prey species avoided open valleys and gorges where the wolves could hunt them.  Eventually, trees grew to house a variety of species of birds and to feed growing populations of beavers.  Beavers built more dams and more fish populations thrived to feed hungry bears.  Without herbivores overgrazing, erosion decreased and plant life along the rivers thrived.  The rivers even changed course because of the stabilization of the riverbanks.