Loss of Predators in Northern Hemiphere Affecting Ecosystem Health
A grizzly bear in Yellowstone National Park. (Credit: Oregon State University)
ScienceDaily (Apr. 9, 2012) —
A survey 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 recently 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 animal populations to greatly increase, crippling the
growth of young trees and reducing biodiversity. This also contributes
to deforestation and results in less carbon sequestration, a potential
concern with climate change.
"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, Northern
Europe 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 wolves, 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
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 preservation or recovery of large predators may represent an
important conservation need for helping to maintain the resiliency of
northern forest ecosystems," the researchers concluded, "especially in
the face of a rapidly changing climate."
The above story is reprinted from materials provided by Oregon State University. Note: Materials may be edited for content and length. For further information, please contact the source cited above.
William J. Ripple, Robert L. Beschta. Large predators limit herbivore densities in northern forest ecosystems. European Journal of Wildlife Research, 2012; DOI: 10.1007/s10344-012-0623-5