Wolf Ecology

Lessons From The Wolf The wolf-effect theory holds that wolves [in Yellowstone] kept elk numbers at a level that prevented them from gobbling up every tree or willow that poked its head aboveground. When the wolves were extirpated in the park as a menace, elk numbers soared, and the hordes consumed the vegetation, denuding the Lamar Valley and driving out many other species. Without young trees on the range, beavers, for example, had little or no food, and indeed they had been absent since at least the 1950s. Without beaver dams and the ponds they create, fewer succulents could survive, and these plants are a critical food for grizzly bears when they emerge from hibernation. After the wolves' reintroduction in 1995 and 1996, they began to increase their numbers fairly rapidly, and researchers began to see not only a drop in the population of elk but a change in elk behavior. The tall, elegant mahogany-colored animals spent less time in river bottoms and more time in places where they could keep an eye out for predatory wolves. If the wolf-effect hypothesis is correct, and wolves are greatly reducing elk numbers, the vegetation should be coming back for the first time in seven decades. Trees are coming back most dramatically in places where a browsing elk doesn't have a 360-degree view; these willows, for example, sit below a rise that blocks the animals' view. A look at the plants shows they have not been browsed at all in several years. Elk don't feel safe here, Ripple contends, because they can't see what is going on all around and are nervous about spending time in this vicinity. Just 50 meters away, however, where the terrain is level and wide open and the elk enjoy a panoramic view, the willows are less than a meter tall and have been browsed much more heavily over the past three years. "It's the ecology of fear," Ripple says.

That's a pretty neat scenario. The article goes on to cite some skeptics who think the changes may have more to do with climate changes than wolf reintroduction. There may be something to that, although the last paragraph I quoted seems to be a good pro-wolf-theory quirk in the data.