As of Wednesday, June 25, 2014
Scientists
have used coyote and red fox fur trapping records across North America
to document how the presence of wolves influences the balance of smaller
predators further down the food chain.
From
Alaska and Yukon to Nova Scotia and Maine, the researchers have
demonstrated that a “wolf effect” exists, favoring red foxes where
wolves are present and coyotes where wolves are absent.
This
effect requires that enough wolves be present to suppress coyotes over a
wide area. Fur trapping records from Saskatchewan and Manitoba reveal
that where wolves are absent in the southern agricultural regions of
each province, coyotes outnumber foxes on average by 3-to-1.
However,
where wolves are abundant in the North, the balance swings dramatically
in favor of foxes on average by 4-to-1 and at an extreme of 500-to-1 at
one site. In
between is a 200-kilometer (124-mile) transition zone where too few
wolves are present to tip the balance between coyotes and foxes.
The
results of the study by Thomas Newsome and William Ripple in the Oregon
State University Department of Forest Ecosystems and Society were
published today in the Journal of Animal Ecology by the British
Ecological Society. “As
wolves were extirpated across the southern half of North America,
coyotes dramatically expanded their range,” said Newsome, a
post-doctoral researcher. “They were historically located in the middle
and western United States, but they dispersed all the way to Alaska in
the early 1900s and to New Brunswick and Maine by the 1970s.” “So
essentially coyotes have been dispersing into wolf and red-fox range in
the North but also into areas where wolves are absent but red fox are
present in the East,” Newsome added.
Newsome
came to the United States on a Fulbright scholarship from Australia
where he earned a Ph.D. from the University of Sydney and specialized in
the study of dingoes, that continent’s top predator. There’s a debate
among Australians, he said, about the potential role of dingoes in
suppressing introduced pests that have already decimated wildlife there.
Over
the last 200 years, Australia has had the highest extinction rate in
the world,” Newsome said. “The debate is about whether the dingo can
provide positive ecological benefits. Where dingoes have been removed,
the impacts of introduced red foxes and feral cats have been quite
severe on native fauna.”
Dingoes
are managed as a pest in New South Wales, the country’s most populous
state. To reduce dingo predation in the livestock industry, Australia
also maintains the world’s longest fence, which runs for 5,500
kilometers (3,400 miles) in an attempt to exclude dingoes from almost a
quarter of the continent.
In
North America, the effect of wolves on coyotes and red foxes provides a
natural case study that can be instructive for Australians.
“Australians can learn a lot from how wolves are managed in North
America, and Americans can learn from the ecological role of the dingo,”
Newsome said.
As
coyotes have expanded in North America, they have become a major cause
of concern for the livestock industry. In the United States in 2004,
researchers estimated annual losses due to coyote predation on sheep and
cattle at $40 million. To reduce those damages, the Wildlife Service of
the U.S. Department of Agriculture has a program to reduce coyote
numbers, an effort that has drawn criticism from conservation groups.
In
reviewing the fur trapping data from two U.S. and six Canadian
jurisdictions, Newsome and Ripple eliminated potential sources of bias
such as records from fur farms that raise foxes. The fur prices of
coyotes and red foxes are also strongly correlated, and the two species
occupy much of the same types of habitat, so they are equally likely to
be targeted and caught in hunters’ traps.
This
study gives us a whole other avenue to understand the ecological
effects of wolves on landscapes and animal communities,” said Ripple. He
has studied the influence of carnivores on their prey — such as deer
and elk — and on vegetation from aspen trees to willows. He and his
colleagues have shown that the removal of top predators can cause
dramatic shifts within ecosystems.
Wolves
are naturally recolonizing many areas of the United States following
their reintroduction into Yellowstone National Park and surrounding
areas in 1995. Scientists are studying wolf interactions with other
species, and in particular, there is interest in determining whether
recolonizing wolves will suppress coyote populations and have cascading
effects on red foxes and other species.
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