Loss of predators in Northern Hemisphere affecting ecosystem health

April 9, 2012
A grizzly bear in Yellowstone National Park. (Photo courtesy of Oregon State University)

A survey done on the loss in the Northern Hemisphere of large predators, particularly wolves, concludes that current populations of moose, deer, and other large herbivores far exceed their historic levels and are contributing to disrupted ecosystems.

The research, published today by scientists from Oregon State University, examined 42 studies done over the past 50 years.

It found that the loss of major predators in forest ecosystems has allowed game to greatly increase, crippling the growth of young trees and reducing biodiversity. This also contributes to and results in less , a potential concern with .

"These issues do not just affect the United States and a few national parks," said William Ripple, an OSU professor of forestry and lead author of the study. "The data from Canada, Alaska, the Yukon, and Asia are all showing similar results. There's consistent evidence that large predators help keep populations of large herbivores in check, with positive effects on ecosystem health."

Densities of large mammalian herbivores were six times greater in areas without , compared to those in which wolves were present, the researchers concluded. They also found that combinations of predators, such as wolves and bears, can create an important synergy for moderating the size of large herbivore populations.

"Wolves can provide food that bears scavenge, helping to maintain a healthy bear population," said Robert Beschta, a professor emeritus at OSU and co-author of the study. "The bears then often prey on young moose, deer or elk – in Yellowstone more young elk calves are killed by bears than by wolves, coyotes and cougars combined."

In Europe, the coexistence of wolves with lynx also resulted in lower deer densities than when wolves existed alone.

In recent years, OSU researchers have helped lead efforts to understand how major predators help to reduce herbivore population levels, improve ecosystem function and even change how herbivores behave when they feel threatened by predation – an important aspect they call the "ecology of fear."

"In systems where large predators remain, they appear to have a major role in sustaining the diversity and productivity of native plant communities, thus maintaining healthy ecosystems," said Beschta. "When the role of major predators is more fully appreciated, it may allow managers to reconsider some of their assumptions about the management of wildlife."

In Idaho and Montana, hundreds of wolves are now being killed in an attempt to reduce ranching conflicts and increase game herd levels.

The new analysis makes clear that the potential beneficial ecosystem effects of large predators is far more pervasive, over much larger areas, than has often been appreciated.

It points out how large predators can help maintain native plant communities by keeping large herbivore densities in check, allow small trees to survive and grow, reduce stream bank erosion, and contribute to the health of forests, streams, fisheries and other wildlife.

It also concludes that human hunting, due to its limited duration and impact, is not effective in preventing hyper-abundant densities of large herbivores. This is partly "because hunting by humans is often not functionally equivalent to predation by large, wide-ranging carnivores such as wolves," the researchers wrote in their report.

"More studies are necessary to understand how many wolves are needed in managed ecosystems," Ripple said. "It is likely that wolves need to be maintained at sufficient densities before we see their resulting effects on ecosystems."

The research was published online today in the European Journal of Wildlife Research, a professional journal.

"The preservation or recovery of large may represent an important conservation need for helping to maintain the resiliency of northern ," the researchers concluded, "especially in the face of a rapidly changing climate."

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8 comments

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Sinister1811
2.2 / 5 (10) Apr 09, 2012
Similar problems exist within the southern hemisphere.
rockymountainj
3 / 5 (4) Apr 09, 2012
This study's assertion that human hunting cannot fill the role of predator hunting is flawed. Perhaps this is true in human hunting's present form. But with smart management techniques, human hunting can absolutely fill this role. How is human hunting fundamentally different in function? It is limited in duration because closed hunting seasons in the fall are designed to maximize herbivore populations and keep them in line with the carrying capacity of the management area. They are limited in area only when remote wilderness areas do not enjoy longer, more liberal open seasons. By designIng wildlife management policies to reflect the goals sought in this study, humans can fill the role of predators without placing pets, children, and farm animals at risk.
jalexmead
5 / 5 (2) Apr 09, 2012
The people who live in wilderness areas should learn to coexist with wolves and other predators. If not then you should move back to the city or suburbs where there are no wild animals. You have no right to exterminate the wolves from all the wilderness areas because you chose to move out there. The wolves have a right to life too! Most of the lands the wolves are on are federal lands which are owned by all the American people not just the people who chose to move out into the wilderness and then call for the elimination of everything that may be dangerous or inconvenient.
ryggesogn2
1 / 5 (2) Apr 09, 2012
Wolves were shot because they attacked cattle and sheep ranchers were trying to raise for people to eat.
Wolves have a right to life? Do human babies have that same right?
jalexmead
5 / 5 (2) Apr 10, 2012
So we are worried about an occasional cow or sheep that is killed by a wolf that the ranchers are compensated for, when 30 to 40 % of the food in America is wasted, and another 20 to 30 % is wasted from overeating.
210
2 / 5 (4) Apr 10, 2012
Wolves were shot because they attacked cattle and sheep ranchers were trying to raise for people to eat.
Wolves have a right to life? Do human babies have that same right?
Human babies? Someone is shooting human babies for the protection of livestock? What are you saying or trying to suggest?
word-
rockymountainj
1 / 5 (3) Apr 10, 2012
The people who live in wilderness areas should learn to coexist with wolves and other predators. If not then you should move back to the city or suburbs where there are no wild animals. You have no right to exterminate the wolves from all the wilderness areas because you chose to move out there.


Where I live in Alberta I coexist quite well with cougars as well as black and grizzly bear. I just don't like that thIs article erroneously suggests that reintroducing wolves into large areas of habitat are the only way to control game animal populations when I am quite happy to collect any extra meat myself.

PS. Wolves don't have rights. We as humans have responsibilities to behave ethically, but that doesn't mean predators lie morally outside the reach of wildland management.
ryggesogn2
1 / 5 (2) Apr 10, 2012
What are you saying or trying to suggest?

Some animal lovers hate people.
So we are worried about an occasional cow or sheep that is killed by a wolf

Trouble is, the predator will find it easier to attack livestock than elk. So what you are really advocating is banning human use of the wolves territory.

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