You wouldn't think that wolves and bears would help each other in the wild. Yet that's exactly what's happening. It turns out that the return of wolves to Yellowstone National Park is beginning to bring back a key part of a grizzly bear's diet: berries.

For the past century, berries have been almost absent from the diets of grizzly bears in Yellowstone, despite the fact that a variety of species grow in the area. Everything from serviceberry to huckleberry once provided bears with the nutrition they needed over the summer. Yet elk have cropped the berry bushes, consuming entire plants and leaving little for the bears to feast on as they prepare to hibernate for winter. The wolf introduction, though, changed all of that. The wolves began to cull the elk herds, scaring them away from habitat that included berry bushes. This became a boon to the grizzlies.

"Wild fruit is typically an important part of grizzly bear diet, especially in late summer when they are trying to gain weight as rapidly as possible before winter hibernation," said William Ripple, one of the researchers, in a news release. "Berries are one part of a diverse food source that aids bear survival and reproduction and at certain times of the year can be more than half their diet in many places in North America."

Elk can be destructive to vegetation without proper predator controls. In fact, herds were responsible for the demise of young aspen and willow trees when wolves were removed from Yellowstone in the early 1900s. Since the wolves were reintroduced in the 1990s, though, these plants have begun to recover, drastically impacting the Yellowstone ecosystem.

"Studies like this also point to the need for an ecologically effective number of wolves," said Robert Beschta, co-author of the study, in a news release. "As we learn more about the cascading effects they have on ecosystems, the issue may be more than having just enough individual wolves so they can survive as a species. In some situations, we may wish to consider the numbers necessary to help control overbrowsing, allow tree and shrub recovery and restore ecosystem health."

The findings are published in the Journal of Animal Ecology.