Ripple and his Oregon State co-author Robert Beschta have documented impacts of cougars and wolves on the regeneration of forest stands and riparian vegetation in Yellowstone and other national parks in North America. Fewer predators, they have found, lead to an increase in browsing animals such as deer and elk. More browsing disrupts vegetation, shifts birds and small mammals and changes other parts of the ecosystem in a widespread cascade of impacts.
Studies of Eurasian lynx, dingoes, lions and sea otters have found similar effects, the authors reported.
Lynx have been closely tied to the abundance of roe deer, red fox and hare. In Australia, the construction of a 3,400-mile dingo-proof fence has enabled scientists to study ecosystems with and without the animals, which are closely related to gray wolves. In some parts of Africa, the decrease of lions and leopards has coincided with a dramatic increase in olive baboons, which threaten farm crops and livestock. In the waters off southeast Alaska, a decline in sea otters through killer whale predation has led to a rise in sea urchins and loss of kelp beds.
The authors call for a deeper understanding of the impact of large carnivores on ecosystems, a view that they trace back to the work of landmark ecologist Aldo Leopold. The classic concept that predators are harmful and deplete fish and wildlife is outdated, they said. Scientists and wildlife managers need to recognize a growing body of evidence for the complex roles that carnivores play in ecosystems and for their social and economic benefits.
Leopold recognized such relationships between predators and ecosystems, Ripple said, but his observations on that point were largely ignored for decades after his death in 1948.
"Human tolerance of these species is a major issue for conservation," Ripple said. "We say these animals have an intrinsic right to exist, but they are also providing economic
|Contact: William Ripple|
Oregon State University