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Wolf response to climate change studied

Pack of Wolves
On Isle Royale, wolves limit the productivity of moose, which limit productivity of fir trees.  

November 5, 1999
Web posted at: 2:13 p.m. EST (1913 GMT)

By Environmental News Network staff

The way wolves respond to significant climate changes can have far-reaching consequences for the ecosystems in which they live, according to a recent study.

In Michigan, on Isle Royale, wolves regulate such a system by limiting the productivity of moose, which limit productivity of fir trees.

"We can't think of wolves as a single species. Instead, we need to think of them as members of a complicated ecosystem," said biologist Rolf Peterson.

The wildlife data used in the study was collected during a long-term and continuing survey directed by Peterson on wolf-moose relationships on Isle Royale National Park.

"Wolves responded to increasingly snowy winters by hunting in larger packs, and consequently, were able to triple the number of moose killed per day compared to less snowy years when they hunted in smaller packs," Peterson said.

Peterson said this greater killing efficiency by wolves brought a decline in the moose population that in turn resulted in less browsing pressure on balsam fir saplings. Just one year following a winter with heavy snows, the saplings showed a noticeable increase in number.

Wolf Pack
The wolves hunted in larger packs during severe winters.  

This type of impact by top-of-the-food-chain predators on lower trophic levels is well known in marine systems, said Peterson, and has been shown to occur in terrestrial systems in the study of invertebrates.

Peterson said that the mean size of wolf packs on Isle Royale ranged from approximately 4.5 animals during least snowy winters to 12 animals during the most snowy winters.

The increase was due primarily to the fact that grown pups who would normally leave the pack to seek mates remained with their family unit during severe winters.

Both wolves and moose found it easier to travel along the shoreline of the island park during heavy snow conditions. This increased encounters between the two species and left more old moose and calves available to wolf predation.

The greater food supply for wolves during snowy winters made them healthier and able to reproduce more successfully, according to Peterson.

"Our best data shows that wolves do have potential to protect the forest. Wolf predation did essentially save elements of the forest that would have disappeared without wolves," Peterson said.

Copyright 1999, Environmental News Network, All Rights Reserved

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Isle Royale National Park
Michigan Technological University
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