The Presence of Brown Bears Reduces the Number of Kills Made by Wolves

Researchers from Utah State University have found that larger brown bear populations deter wolves. Wolves make less kills when more brown bears are present. The findings have surprised scientists since it was expected that they would kill more prey when competing with bears. The details were just published in the journal Proceedings of the Royal Society B.

Grey wolves (Canis lupus) and brown bears (Ursus arctos) often have overlapping ranges and may occasionally interact. Both species are apex predators, animals that are at the very top of their ecosystem’s food chain, lacking natural predators. Other examples of apex predators are lions, tigers, and killer whales. Apex predators are often important to the ecosystems they reside in since they keep herbivore populations in check. This in turn helps manage damage to trees and other plants. Although overlapping apex predators may not actively fight, they can sometimes compete for resources. Previous research has showed that brown bears sometimes steal wolf kills; the wolves aren’t strong enough to fight back and will generally end up abandoning the prey item.

Ecologists investigated whether or not the presence of brown bears, which steal wolf kills, would impact how grey wolves hunt. The team studied wolf packs at sites in the Yellowstone National Park in Wyoming and throughout Scandinavia. The researchers used GPS and observational data to record kills and population densities.

Interestingly, the grey wolves didn’t increase their hunting activity to make up for lost kills to brown bears. Instead, the wolves killed less when brown bears were present. Previously, ecologists had suggested that wolves may need to kill more prey when they had to compete with bears. It’s possible that wolves prefer to hunt when there are no brown bears in the area, reducing the chance of having their food stolen. Another theory is that they’re simply not finding the same number of prey items; young deer are easy for both bears and wolves to capture.

The team’s results show that brown bears actually reduce the number of kills made by grey wolves, the opposite of what scientists had expected. The authors emphasize the importance of considering interactions between apex predators when studying complete ecosystems.

REFERENCE

Tallian et al. Competition between apex predators? Brown bears decrease wolf kill rate on two continents. Proceedings of the Royal Society B (2017).

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