Absence of top predators puts ecosystems awry at the expense of other species
By Summit Voice
SUMMIT COUNTY — The absence of wolves has thrown some western ecosystems out of balance at the expense of other species — including threatened Canada lynx, according to new research published this week in the Wildlife Society Bulletin.
The study suggests that lynx are struggling at least partly because of a decline in snowshoe hare populations, and that the loss of hares in turn may be caused by coyote populations that have surged to fill the ecological niche formerly filled by wolves. Biologists use the term trophic cascade to describe the ripple effects that missing predators can have on entire ecosystems.
Where wolves recovered, as in Yellowstone National Park, coyote populations were initially reduced by 50 percent. Although more sampling will be required, early evidence indicates that a snowshoe hare recovery may be taking place.
An increase in secondary mesopredators has been documented in a wide range of ecosystems on land and in the sea and has caused significant disruptions. In this case, it has possibly contributed to the decline of a threatened species, the scientists said.
“The increase in mesopredators such as coyotes is a serious issue; their populations are now much higher than they used to be when wolves were common in most areas of the United States,” said William Ripple, a professor in the Department of Forest Ecosystems and Society at Oregon State University.
“Before they were largely extirpated, wolves used to kill coyotes and also disrupt their behavior through what we call the ‘ecology of fear,’” Ripple said. “Coyotes have a flexible, wide-ranging diet, but they really prefer rabbits and hares, and they may also be killing lynx directly.”
The researchers did not say whether wolves might also kill lynx directly.
In numerous studies in recent years, researchers have documented how the presence of wolves and other large predators helps control populations of grazing ungulates including deer and elk, and also changes their behavior. Where wolves have become established, this is allowing the recovery of forest and stream ecosystems, to the benefit of multiple plant and animal species.
Lacking the presence of wolves or other main predators in both terrestrial and marine environments, populations of smaller predators have greatly increased. Other studies have documented mesopredator impacts on everything from birds to lizards, rodents, marsupials, rabbits, scallops and insects. This includes much higher levels of attacks by coyotes on some ranch animals such as sheep, and efforts attempting to control that problem have cost hundreds of millions of dollars.
Scientists have concluded that exploding mesopredator populations can be found in oceans, rivers, forests and grasslands around the world.
“In the absence of wolves, coyote densities and distributions generally expanded in theU.S., into the Midwest, to the northeast as far as Newfoundland, and as far northwest as Alaska,” the researchers wrote in their report.
As these issues are factored into decisions about how to manage wolves, the researchers said, it’s also important to maintain what they call “ecologically effective” wolf populations, the researchers wrote in their study. The full value of these top predators, and the numbers of them it takes to achieve a wide range of ecological goals, should be more thoroughly researched and better understood, they said.
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