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an aggressive program of lake trout control, but at best,
the program manages merely to hold down the lake
trout population: eradication of this non-native invader
a third important food source for grizzlies has been
diminished since the reintroduction of wolves in 1995:
the bears formerly fed extensively on winter-killed elk
and bison when they emerged from their dens in the
spring, but now the wolves are consuming many of
Surprisingly, despite the decline of three key food
resources, grizzly numbers in the GYe have increased
themselves to be genuine opportunists, shifting to
alternative resources when a preferred food source is
in short supply. the grizzlies are now killing more elk
calves than they did before the decline of cutthroat
the bears also feed on berries, succulent plants, fleshy
roots, insects, and mushrooms when they are avail-
with the effects of climate change and non-native spe-
cies, although there surely are limits to what they can
endure.
matically from approximately 19,000 animals in 1994
to only about 6,000 in 2010 (see fig. 15.13). However,
a recent assessment determined that wolf predation by
itself was not sufficient to account for the drop in elk
numbers. contributing to the decline were increased
predation of elk calves by grizzly bears, as described
previously, along with drought and elk hunting outside
sionally bison, deer, pronghorn, and moose, but hun-
dreds of cattle and sheep were taken as well (though
less than 3 percent of livestock losses in the area can
be attributed to predation). compensation programs for
livestock losses were initiated by a nongovernmental
organization, Defenders of Wildlife, and then adopted
to varying degrees by state game and fish departments.
the costs of conserving biological diversity can be sub-
stantial when large predators are involved, but the ben-
efits are also obvious. For example, wolves and grizzlies
there also are thought to be ecological benefits. Fol-
lowing the sharp decline in elk numbers on Yellow-
stone's northern range, ecologists William Ripple and
Robert Beschta proposed that the associated reduction
in browsing pressure had allowed sprouts of aspen, wil-
lows, and other woody riparian plants to grow tall again
their suggested mechanism involved not just the reduc-
tion in elk numbers but also a change in elk behavior.
With wolves, they postulated, the elk moved around
more often, avoiding habitats where they would be
more vulnerable to wolf predation. According to Ripple
and Beschta's hypothesis, such movements might be
in response to detection of a wolf in the distance. in
both cases, the result would be less time spent browsing
in any particular place, allowing more sprouts to grow
tall. though an intriguing concept, other research has
sprouts on the northern range still have not elongated
into new tree-sized stems, except within fenced exclo-
Unlike aspen, willows have become conspicuously
taller since about 2000 in some well-watered places,
such as along the Lamar River near Soda Butte creek,
perhaps due partially to the presence of wolves. How-
ever, increased willow growth has not been observed
everywhere. colorado State University scientists Kristen
Wolves, Elk, and Aspen
By the early twentieth century, the wolf was function-
ally extinct across most of the West, and it was one
of the first species to be protected after passage of the
tor eradication in YnP had been questioned as early as
the 1930s, and the possible role of the wolf in control-
Wolf reintroduction gained considerable public support
at that time, but it was not until 1995 that 14 wolves
were captured in Alberta and released into YnP's north-
2012 there were several hundred in the area (about 100
in YnP).
critics worried that wolves would reduce elk herds to
the point of impairing big-game hunting opportunities,
and that they would prey heavily on livestock outside
example, the northern Yellowstone elk herd fell dra-
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