Guardian: Grey wolves have returned to Yellowstone National Park, raising hopes that the area's ecosystem has bounced back. But the reintroduction of these mighty predators isn't enough to enable a full recovery, scientists say.
In the early 1900s, wolves largely vanished from Yellowstone. In their absence, elk -- which were no longer hunted by wolves -- ate more willows by streams. Without enough food or material to build their dams, beavers also declined. That made the willows' situation even worse, because...