When wolves left an area near Banff, Alta., elk became more common, a meadow replaced willow trees, and songbirds were replaced by sparrows, biologists say.
In the mid-1980s, wolves naturally recolonized the Bow Valley in Banff National Park, except for areas near the town itself.
Mark Hebblewhite of the University of Alberta in Edmonton and his colleagues have found the exclusion of the wolves caused major changes in the area's food chain.The study in the August issue of the journal Ecology is one of the first large-scale studies to show the key role of a top predator on land.
"Those effects trickled in a cascading fashion down the trophic [nutritional] levels from the highest carnivore to the herbivores, elk, down to vegetation," Hebblewhite said.
Since wolves feed on elk, the number of herbivores jumped without the predators. Elk populations were 10 times as high in the low-wolf area compared to where many wolves roamed, the team found.
"Where there's lot of elk, it's like a lawnmower's gone through and mowed everything down," Hebblewhite said. "There's no young aspen."
Beaver populations, which depend on willow to build their dams, also seemed to decline. Songbirds like the American redstart also vanished from the area without wolves.
In contrast, inside the fence where there are no elk, tall willows and aspens are still growing and songbirds are chirping.
The natural experiment shows the importance of using conservation strategies to protect top predators, the team said.
Researchers at the University of Alberta, Parks Canada, University of Guelph and University of Calgary co-authored the study.
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