Recolonizing wolves influence the realized niche of resident cougars

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.

Ecological niche partitioning within a large predator guild in a nutrient‐limited estuary

“…As such, nutrient and resource limitations likely are important drivers of population‐, community‐, and ecosystem‐level processes within the ecosystem, including interspecific interactions and resource use by large‐bodied predators. Results support our hypotheses that niche partitioning occurs among the most abundant species within the aquatic predator guild, which is likely facilitated by a variety of factors including character displacement and interspecific differences in life‐histories (e.g., Schluter and McPhail ; Fedriani et al ; Elboch et al ).…”

“…Of particular importance for understanding the potential impacts of changes in predator abundance is the extent of trophic redundancy within predator guilds (i.e., whether the role of a particular species might be filled by another), which is thought to dictate ecosystem resilience (e.g., Peterson et al ; Mouillot et al ). Recent research suggests that predator guilds often thought to be ecologically similar actually show some degree of niche partitioning, which also occurs within populations through ontogenetic niche shifts and individual specializations (e.g., Rosenfeld ; Bolnick et al ; Elboch et al ). Elucidation of niche partitioning within coastal estuarine communities can thus facilitate improved understanding of both food web dynamics and community responses to environmental perturbations and anthropogenic impacts.…”

Multiple anthropogenic interventions drive puma survival following wolf recovery in the Greater Yellowstone Ecosystem

“…As elk decreased, starvation across age classes and predation on kittens both increased (Figure ). Decreasing elk availability over the course of our study was likely influenced by three contributing factors: first, the Jackson herd was actively reduced following management objectives; second, over the course of our study, a larger proportion of the remaining Jackson herd wintered on the NER (Cole, ; WGFD ), where they were less available to pumas because of the NER's open expanses without cover and the presence of wolves and people (Elbroch et al., ); third, re‐established wolves likely limited elk availability and accessibility through exploitive and interference competition (Elbroch, Lendrum, Newby et al., ; Kortello et al., ), discussed further below. State wildlife managers, in fact, speculated that elk shifted their distributions to the NER, where they were less available to pumas, due to a combination of wolf predation and earlier winter snowfalls (WGFD, ).…”

“…We split each year into two 6‐month seasons, following legal hunting periods for pumas, which we expected to yield differences in age‐specific survival and mortality rates because human‐caused mortality is generally the driver of puma population dynamics across hunted populations (Quigley & Hornocker, ; Stoner et al., ): (a) we defined the “hunting season” as 1 October to 31 March of the following year, during which pumas were legally hunted. The hunting season also captured the following additional ecological variation: elk returned to low‐elevation winter ranges in November and aggregated in large herds near supplementary feeding stations, deer migrated out of the study area, competition between wolves and pumas likely increased near shared prey, and deep snows and cold temperatures increased the risk of starvation (Elbroch, Lendrum, Newby, Quigley & Thompson, ; Elbroch et al., ); (b) We defined the “nonhunting season” as 1 April–30 September, during which puma hunting was closed, and during which elk migrated to summer ranges at higher elevations and became more widely dispersed, deer returned becoming an integral part of local puma diets, temperatures warmed, and ungulate and puma parturitions occurred (Elbroch, Lendrum, Alexander & Quigley, ; Elbroch, Lendrum, Newby et al., ).…”

“…Elbroch, Lendrum, Newby et al, 2015).For our second time-based covariate, we divided our study into two time periods, primarily reflecting "low-wolf" and "high-wolf" densities. We selected a cut-off date ofDecember 31, 2005, as …”