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Wolves as Engineers of Biodiversity

Today, wolves recovering in the Northern Rockies are known as the “engineers of biodiversity.” Time Magazine Jan.’98, reports, ”... An ecosystem stripped of the wolf doesn’t simply become more peaceable; rather, it becomes flabby and unbalanced.” With the dominant predator gone, the next biggest hunter-typically the coyote-assumes the top spot. As the coyote population explodes, the populations of foxes, badgers and martens, which compete with coyotes for rodents and other small game, dwindle. Large prey such as elk, which were once brought down by wolves, begin to multiply excessively, stripping vegetation from highlands, and denuding riparian habitat of valuable stream side cover such as aspen and willow. And with few elk carcasses to be found, scavengers like magpies, ravens and grizzly bears, accustomed to dining on scraps from wolf kills, have to scrounge elsewhere for protein. “The wolf is a keystone species,” says Yellowstone biologist Douglas Smith. “You remove it and the effects cascade down to the grasses.”

Kevin Nahler

Photo Credit: Kevin Nahler

In Yellowstone, that cascade effect has long been felt. Since the 1930s, wildlife managers have watched in dismay as the park’s ecosystem -- once well-balanced between predator and prey -- grew more and more bottom-heavy. Finally, in the 1970s, they decided to do something about it. Working through the then newly-enacted Federal Endangered Species Act, they proposed a plan under which wolves would be imported from Canada to reclaim their place in the ecosystem.

Twenty years later, the plan was approved, and wolves were captured and transported by airplane across the border, and then by truck and even by mule-drawn wagons in 1995 and 1996 to Yellowstone (31 wolves) and to Idaho (35 wolves). A third wolf population was starting to recolonize northwestern Montana by natural migration from Canada in the late 1970s-early 1980s. These three separate recovery areas provided excellent habitat for the wolves to breed and expand their territories, and today the combined wolves from these three regions are known as the Northern Rockies gray wolf population.

The impact of the return of this key predator and its contribution to establishing a healthy, functioning ecosystem is now apparent:

Around Yellowstone, elk kills are common, a welcome development for park managers hoping to bring that animal’s population back to manageable levels, and the elk themselves have become more wary and less apt to stay in any one place for long periods of time.

Kevin Nahler

Photo Credit: Kevin Nahler

Wolf-killed carcasses of elk, deer and bison provide plenty of left-overs for other animals to scavenge, a symbiotic relationship that had existed for thousands of years before wolves were exterminated from the Park.

This reinstated wolf presence has reduced the coyote population of the Park by fifty percent (and even more in some areas), since wolves view other canids as territorial competition. This has opened up ecological “breathing room” for foxes and other species in areas where the coyote population had unnaturally exploded in the absence of wolves. Recent evidence suggests that the wolf’s reduction of the coyote population has even resulted in higher survivorship rates of the fawns of pronghorn antelopes, highly favored by coyotes.

Even riparian and highland vegetation, no longer over-grazed by hungry elk who now keep on the move in the historical dance between predator and prey, is expected to start making a comeback. Results from studies initiated soon after wolf reintroduction are already showing signs of this recovery in riparian areas where willow and aspen growth is flourishing. This woody riparian habitat provides nesting and roosting spots for migrating songbirds, shade over the rivers that keep temperatures cool and favorable for juvenile fish, roots that add stability to streambanks from erosion, and woody material used by beavers to construct dams. “We’re seeing beneficial effects from the top down,” says Robert Crabtree, a wildlife ecologist. “Who knows how far it will go?”

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