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Competition between apex predators? Brown bears decrease wolf kill rate on two continents; Tallian A et al. 2017 Proc. R. Soc. B 284: 20162368. http://dx.doi.org/10.1098/rspb.2016.2368
Topic Started: Feb 8 2017, 08:17 PM (721 Views)
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Why grey wolves kill less prey when brown bears are around

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Food fight
Wild Wonders of Europe/Widstrand/Naturepl.com

By Brian Owens

Wolves may be better at sharing their meals with bears than we thought.

Biologists have long assumed that when wolves and brown bears share territory, the wolves are forced to kill more often to make up for the food stolen by scavenging bears.

But when Aimee Tallian, a biologist at Utah State University, and her colleagues looked for evidence of this, they found the opposite. Where wolves live alongside bears in Scandinavia and Yellowstone National Park in the US, they actually kill less often.

“People had this general assumption, because you do see lynx and mountain lions abandon their kills once a bear takes it over, but no one had really looked at this in wolves before,” she says.

It’s not yet clear why this might be, but Tallian has a few theories.

Waiting for leftovers

One is that in winter, when wolves normally kill large animals like moose, there is enough meat on the carcass that it is worthwhile for the pack to spend a few extra days waiting around for leftovers after a scavenging bear is done with it, instead of going off to make another kill.

Another is that in spring and summer both wolves and bears prey on baby moose, and this competition over a finite resource might make it harder for both of them to find prey.

It’s probably some combination of the two, says Tallian, which will require further study to sort out. “We want to look at what component of that kill interval the bears are actually changing,” she says.

Heather Bryan, a biologist at the University of Victoria, Canada, says it may be impossible to generalise the results to other wolf and bear populations, because the dynamics of carnivore populations can change drastically depending on everything from food availability, the season and individual members of a pack. So there may be no specific lessons for conservationists protecting wild populations.

But the general principle of considering complex, multispecies interactions is vital. “The idea of thinking about the whole ecosystem and species interactions is important in conservation,” Bryan says.wol

https://www.newscientist.com/article/2120620-why-grey-wolves-kill-less-prey-when-brown-bears-are-around/




Journal reference:
Tallian A et al. 2017 Competition between apex predators? Brown bears decrease wolf kill rate on two continents. Proc. R. Soc. B 284: 20162368. http://dx.doi.org/10.1098/rspb.2016.2368

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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