For grizzly bears and wolves in Yellowstone, competing for food has unexpected results

Sharing a meal with a greedy table companion creates strained relationships, especially when there are claws and fangs.

For wolves and grizzly bears in Yellowstone National Park, the competition for a dead-end dinner has unexpected results. When a bear steals food from a pack of wolves, wolves kill less often.

“What we did was break the wolf’s feeding sequence,” University of Montana researcher Matthew Metz told the Missoulian. “We’ve studied their research time and their manipulation time: the amount of time they spend eating and digesting their deaths.”

And especially in the spring, when Yellowstone elk herds are giving birth to thousands of staggering calves across the Lamar Valley and all the predators around the cruises for fresh protein, grizzly bears lean on wolves. a way that changes the behavior of wolves. The reduction in wolf deaths when there are grizzlies has also been seen in a paired study of Scandinavian predators.

“Wolves put extra food into the landscape for bears,” said Norwegian Nature Research Institute scientist Aimee Tallian, who collaborated with Metz through UM’s Yellowstone Wolf Project. “But bears are antagonistic to wolves. They take part in the supply of shared prey and usurp the slaughter of wolves. So wolves help bears, but bears don’t necessarily help wolves much.”

The Great Yellowstone ecosystem surrounding Yellowstone National Park has the second largest concentration of grizzlies in the lower 48 states. It is estimated that about 1,000 grizzlies pack between five and 13 per 100 square miles.

In comparison, Scandinavia has about 3,000 rough bears (the same species as US grizzly bears). But they are scattered about three bears per 100 square kilometers across Norway and Sweden. And they feed on tall ones, which are not grouped like elk, but exist in similar numbers to Scandinavian forests.

“They’re controversial there, too,” Tallian said of bear relations on the other side of the Atlantic Ocean.

Scandinavia also has a large wolf population, which inhabits regions with and without wild bears. This added complexity to the study, because researchers could contrast wolf behavior with and without urine competition.

“The fact that we’re seeing patterns in various places suggests that these patterns exist where wolves and bears persist together,” Tallian said. “That’s a big part of their habitat.”

Comparing American and Scandinavian meats has other complications. In Yellowstone, wolves and grizzlies also have to compete with black bears, which do not exist in Europe.

While competition from grizzlies tends to reduce wolf death rates, it has the opposite effect on mountain lions. Metz said lions in the land of bears are also expelled from their deaths by grizzlies and then have to kill more to stay fed.

The relationship may change from place to place. Along Alaska salmon streams, for example, Kodiak brown bears usually eat only the heads of spawning fish, leaving a large amount of body meat to follow the wolves.

It remains to be seen exactly why and how these inter-species death rates are balanced. But Tallian and Metz agreed that the opportunity to study several major predators working in the same landscape was enlightening.

“Relatively little was known about how bears affected wolf feeding dynamics,” Metz said. “Our work begins to fill the gap by showing that the dynamics are different and provide another reminder of how changes in the complexity of the ecosystem, in this case, the presence of bears, affect the behavior of other species.” .

“A great way to think about that is the historical context,” Tallian added. “This is probably what these systems have looked like for thousands of years, with this dynamic interaction of competitors in the landscape. There are very few places that feel so intact these days, where ecosystems can play on their own.”

In:
• to the bru
• Yellowstone National Park