Loss of Wolves Changes Canadian Ecosystem
WASHINGTON The loss of once-plentiful wolves in a part of Canada's west allowed the elk population to mushroom, pushing out beavers and songbirds and showing the importance of top predators, Canadian researchers said Monday.
Although scientists have long noted that the loss of even one species can have profound effects, the report is one of the first large-scale studies to show clearly the widespread consequences of losing a predator at the top of the food chain.
Mark Hebblewhite of the University of Alberta, and colleagues studied what happened in "a serendipitous natural experiment" when wolves returned to part of the Bow Valley of Banff National Park in Alberta.
Wolves were driven out in the 1960s "because that's what we did then," Hebblewhite said.
"The first wolf pack recolonized the Bow Valley of Banff National Park in 1986. High human activity partially excluded wolves from one area of the Bow Valley, whereas wolves made full use of an adjacent area," the researchers wrote in their report, published in the journal Ecology.
Willow trees, river-loving birds called willow warblers and American redstarts, and beaver dams once were common in Bow Valley and surrounding areas. But in the areas where wolves remained scarce and elk populations mushroomed, these plants and animals were less common.
The wolves clearly had a major effect on elk. Elk populations were 10 times as high in areas where there were no wolves, Hebblewhite's team found.
This meant that elk could be found in suburban backyards, and sometimes on hiking trails. "Seven people are sent to hospitals every year on average by getting into a fight with an elk," he said. "They are 250 kg (550 pounds) on average so you don't want to get into a fight with one. But being a park they couldn't just go willy-nilly shooting elk and as a society we have advanced beyond wildlife management by just shooting things."
The elk browsed on tender young willows, leaving little for beavers and willow-dwelling birds. Aspen trees seemed less affected.
"We also found that as elk populations climbed, active beaver lodges declined, probably because beavers could no longer find sufficient trees with which to build their dams," Hebblewhite said in a statement.
But in the parts of the park where wolves returned, the elk populations in affected areas fell and willows were coming back.
While other predators such as grizzlies might have played a role, Hebblewhite's team noted, bears were never completely driven from the park while wolves were.
"Yes, wolves are ecologically important. It (the study) bolsters the importance of conserving species like wolves and other top carnivores," Hebblewhite said.