Rivers

Wolves were once native to the Yellowstone National Park — until hunting wiped them out. But when the wolves began to come back, something interesting happened: the rest of the park began to find a new, more healthful balance. When the grey wolf was reintroduced into the Yellowstone Ecosystem in 1995, for example, there was only one beaver colony in the park. Today, the reintroduction of wolves continues to astonish biologists with a ripple of direct consequences throughout the ecosystem including other flourishing species populations.