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Wolves Help Bears Get Their Berries

Jul 08, 2014 05:57 PM EDT
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No, wolves are not sidling up to a friendly grizzly bear to offer a bushel of berries, but they are helping in their own way. Researchers have found that recovering wolf populations in North America are culling elk numbers, leaving more berries for sweet-toothed grizzlies to munch on.

 According to a study published in the Journal of Animal Ecology since grey wolf populations have risen in Yellowstone National Park, the average proportion of fruit in grizzly scat has risen significantly.

"The grizzly bear uses some of the same plants that the prey of the wolf uses," lead author of the study, William Ripple,  told the Los Angeles Times. "The reintroduction of one top predator is potentially affecting another top predator through this food web."

According to Ripple and his colleagues, elk herds browse on trees and shrubs in Yellowstone National Park. However, the elimination of natural wolf populations in most of North America in the 1920s had resulted in elk numbers to grow out of control.

The result was the over-browsing of many berry-producing shrubs that bears also relied on.

Wolves were finally reintroduced to Yellowstone in 1995 and have since been gradually recovering. Recently, wolf populations have found their way back into other parts of North America as well, bullying out overpopulated coyote, elk, and deer across the states and restoring things to how they were 70 years ago.

"We're in the early stages of this ecosystem recovery. This is what we call passive restoration," Ripple said. "We put the wolf back in and then we let nature take its course."

Still, while the bears may be benefitting from better access to berry crops, the reintroduction of wolves may also lead to less access to another kind of food source, elk.

"Bears eat elk and bear numbers have increased three or four times during the [post-wolf] period," Arthur Middleton of Yale University told BBC News.

While bears don't focus elk populations as heavily as wolves do, the expert explained that elk calves are an important food source for grizzlies in the spring.

"Bears and wolves together reduce elk numbers, and it may be that as elk numbers have declined some bears have sought out alternative foods such as berries," said Middleton, offering another explanation for the bears' sudden interest in berries that is separate from shrub re-growth.

The authors of the study do admit that the complex web of the Yellowstone ecosystem is nothing as simple as "wolves help berries help bears," but understanding that single facet can certainly help develop a greater understanding overall.

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