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Animals regulate their numbers by own population density

Zoologists from the University of Toronto have cracked the ecological puzzle of how animals - in this case the arctic ground squirrel - manage to control their own population in the northern boreal forest of Canada.

In a study to be published in the Nov. 23 issue of Nature, the researchers found that when arctic ground squirrel populations reached the maximum limit the environment could support, the females severely reduced reproduction and most died over winter during hibernation, thus controlling the population.

"No population of organisms increases without limit. The central question in population ecology is what regulates their numbers. And the answer often is: the actions of the populations themselves," says Rudy Boonstra, a professor of zoology in the Division of Life Sciences at the University of Toronto at Scarborough and co-author of the paper. "The populations themselves are critical to preventing unlimited growth. There are obviously other processes going on - predators and things like that - but the regulation that occurs in arctic ground squirrels is mainly dictated by the number of fellow squirrels that are around it."

"Animals can change their reproductive output depending on certain environmental conditions. And one of those environmental conditions is population density," notes Tim Karels, lead author of the paper who conducted the research as part of his PhD thesis at U of T. "So if you have lots of neighbours and you're competing for the same food, it can lower reproduction. And that's what we saw. At very high population densities, female ground squirrels basically shut down their reproduction, and that was done in order to sustain their own survival. When conditions were better, they would start reproducing again."

The arctic ground squirrel lives in the tundra, alpine and forested regions of the Northwest Territories, the Yukon and Alaska and hibernates over winter. Karels conducted the research between the spring of 1996 an
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Contact: Janet Wong
jf.wong@utoronto.ca
416-978-6974
University of Toronto
22-Nov-2000


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