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Vol. 54, 2015
Recolonizing wolves
influence the realized niche of resident cougars
L
Mark Elbroch1*, Patrick E Lendrum1, Jesse Newby2,
Howard Quigley1 and Daniel J Thompson3
1Panthera,
8 West 40th Street, 18th Floor, New York, NY 10018, USA
2Craighead Beringia South, PO Box 147, Kelly, WY
83011, USA
3Wyoming Game and Fish, 260 Buena Vista, Lander, WY
82520, USA
Abstract
Background: Niche
differentiation may betray current, ongoing competition between two
sympatric species or reflect evolutionary responses to historic
competition that drove species apart. The best opportunity to test
whether ongoing competition contributes to niche differentiation is to
test for behavioral shifts by the subordinate competitor in controlled
experiments in which the abundance of the dominant competitor is
manipulated. Because these circumstances are difficult to coordinate in
natural settings for wide-ranging species, researchers seize
opportunities presented by species reintroductions. We tested for new
competition between reintroduced wolves and resident cougars in the
Southern Yellowstone Ecosystem to assess whether wolves might be
impacting the realized niche of sympatric cougars.
Results: Between
2002 and 2012, a period during which wolves increased from 15 to as
high as 91 in the study area, cougars significantly increased the
percentage of deer and decreased the percentage of elk in their diet in
summer. Our top models explaining these changes identified elk
availability, defined as the number of elk per wolf each year, as the
strongest predictor of changing cougar prey selection. Both elk and
deer were simultaneously declining in the system, though deer more
quickly than elk, and wolf numbers increased exponentially during the
same time frame. Therefore, we concluded that prey availability did not
explain prey switching and that competition with wolves at least
partially explained cougar prey switching from elk to deer. We also
recorded 5 marked cougar kittens killed by wolves and 2 more that were
killed by an undetermined predator. In addition, between 2005 and 2012,
9 adult cougars and 10 cougar kittens died of starvation, which may
also be in part explained by competition with wolves.
Conclusions: Direct
interspecific predation and shifting cougar prey selection as wolves
increased in the system provided evidence for competition between
recolonizing wolves and resident cougars. Through competition,
recolonizing wolves have impacted the realized niche of resident
cougars in the Southern Yellowstone Ecosystem (SYE), and current
resident cougars may now exhibit a realized niche more reflective of an
era when these species were previously sympatric in the Yellowstone
Ecosystem.
Key words: Canis
lupus; Competition; Prey
switching; Puma concolor;
Realized niche; Wyoming; Yellowstone.
*Correspondence: E-mail: melbroch@panthera.org
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