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Carcass-stealing by grizzlies doesn’t mean wolves kill more
Different worlds
Carcass-stealing by grizzlies doesn’t mean wolves kill more
“It’s a baffling finding,” said Doug Smith, Yellowstone’s wolf biologist. “To be honest, for 20 years I’ve been saying bears increase wolf kill rates because bears steal so many carcasses.”
That data from two very different ecosystems pointed to the same conclusion helped convince Yellowstone bear biologist Kerry Gunther that the research was “not just a fluke.”
The study’s lead author was Aimee Tallian, a Utah State University wildlife ecologist and former Yellowstone research assistant. Eleven international co-authors helped with the National Science Foundation-funded project that allowed Tallian to spend a year working in Sweden.
Different worlds
The research area in south-central Sweden is very different from Yellowstone, Tallian noted. Roads criss-cross the dense forest because it is logged. That means researchers could drive to most locations, compared to Yellowstone where hours spent hiking is more often the norm.
“It’s heavily managed by humans, but there are still a lot of woods and remote areas,” she said.
Yellowstone is also unusual in that grizzly-wolf interactions are sometimes seen along the main roads where they are photographed by tourists or studied through spotting scopes. Seeing the animals in Sweden is rare, partly because they are still hunted populations.
Ecologist Aimee Tallian
Research says
Ecologist Aimee Tallian
Research says
Tallian said the assumption that the presence of an apex predator like grizzlies would drive wolves to hunt and kill more prey was never written down anywhere, but was a commonly held belief.
“The results were the opposite of what we expected,” she said. “I double-checked the data so many times thinking, ‘What did I do wrong?’”
“Our results challenge the conventional view that brown bears do not affect the distribution, survival or reproduction of wolves,” stated the research paper, which was published in the “Proceedings of the Royal Society B” on Feb. 8.
“Although the outcome of interactions between bears and wolves at carcasses varies, bears often dominate, limiting wolves' access to food,” the paper said. “Furthermore, our findings suggest that wolves do not hunt more often to compensate for the loss of food to brown bears. In combination, this implies that bears might negatively affect the food intake of wolves," so wolf populations that live within the same geographical area as brown bears may see effects on their fitness.
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Research
We used long-term datasets from Scandinavia (Europe) and Yellowstone National Park (North America) to evaluate how grey wolf (Canis lupus) kill rate was affected by a sympatric apex predator, the brown bear (Ursus arctos).
We used kill interval (i.e. the number of days between consecutive ungulate kills) as a proxy of kill rate. Although brown bears can monopolize wolf kills, we found no support in either study system for the common assumption that they cause wolves to kill more often. On the contrary, our results showed the opposite effect.
In Scandinavia, wolf packs sympatric with brown bears killed less often than allopatric packs during both spring (after bear den emergence) and summer. Similarly, the presence of bears at wolf-killed ungulates was associated with wolves killing less often during summer in Yellowstone.
The consistency in results between the two systems suggests that brown bear presence actually reduces wolf kill rate. Our results suggest that the influence of predation on lower trophic levels may depend on the composition of predator communities.
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Research
Competition between apex predators? Brown bears decrease wolf kill rate on two continents
Abstract
Trophic interactions are a fundamental topic in ecology, but we know little about how competition between apex predators affects predation, the mechanism driving top-down forcing in ecosystems.
We used long-term datasets from Scandinavia (Europe) and Yellowstone National Park (North America) to evaluate how grey wolf (Canis lupus) kill rate was affected by a sympatric apex predator, the brown bear (Ursus arctos).
We used kill interval (i.e. the number of days between consecutive ungulate kills) as a proxy of kill rate. Although brown bears can monopolize wolf kills, we found no support in either study system for the common assumption that they cause wolves to kill more often. On the contrary, our results showed the opposite effect.
In Scandinavia, wolf packs sympatric with brown bears killed less often than allopatric packs during both spring (after bear den emergence) and summer. Similarly, the presence of bears at wolf-killed ungulates was associated with wolves killing less often during summer in Yellowstone.
The consistency in results between the two systems suggests that brown bear presence actually reduces wolf kill rate. Our results suggest that the influence of predation on lower trophic levels may depend on the composition of predator communities.
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