Cougar survival and source‐sink structure on Greater Yellowstone's Northern Range

Abstract

We studied survival and causes of mortality of radiocollared cougars (Puma concolor) on the Greater Yellowstone Northern Range (GYNR) prior to (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994) and after wolf (Canis lupus) reintroduction (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) and evaluated temporal, spatial, and environmental factors that explain variation in adult, subadult, and kitten survival. Using Program MARK and multimodel inference, we modeled cougar survival based on demographic status, season, and landscape attributes. Our best models for adult and independent subadults indicated that females survived better than males and survival increased with age until cougars reached older ages. Lower elevations and increasing density of roads, particularly in areas open to cougar hunting north of Yellowstone National Park (YNP), increased mortality risks for cougars on the GYNR. Indices of ungulate biomass, cougar and wolf population size, winter severity, rainfall, and individual characteristics such as the presence of dependent young, age class, and use of Park or Wilderness were not important predictors of survival. Kitten survival increased with age, was lower during winter, increased with increasing minimum estimates of elk calf biomass, and increased with increasing density of adult male cougars. Using our best model, we mapped adult cougar survival on the GYNR landscape. Results of receiver operating characteristic (ROC) analysis indicated a good model fit for both female (area under the curve [AUC] ¼ 0.81, 95%CI ¼ 0.70-0.92, n ¼ 35 locations) and male cougars (AUC ¼ 0.84, 95%CI ¼ 0.74-0.94, n ¼ 49 locations) relative to hunter harvest locations in our study area. Using minimum estimates of survival necessary to sustain the study population, we developed a source-sink surface and we identify several measures that resource management agencies can take to enhance cougar population management based on a source-sink strategy. ß 2011 The Wildlife Society.

Recolonizing wolves influence the realized niche of resident cougars

“…Instead, our results better support an alternate explanation for how competition may be playing out between wolves and cougars in the SYE-one that suggests that changing cougar prey selection was driven by changing cougar habitat use. If cougars have shifted to more complex habitats to mitigate direct interference competition with coursing wolves, as has been shown in Northern Yellowstone (Ruth et al 2011(Ruth et al , 2015, then this shift in habitat use likely led to increased encounter rates with more forest-dependent mule deer. In support of this hypothesis, we did in fact detect an increase in the percentage of kill sites found in forested habitats in summers over the course of the study.…”

“…Atwood et al (2007) reported that cougars increased predation on elk (Cervus elaphus) and reduced predation on mule deer (Odocoileus hemionus) with the recolonization of wolves in southwest Montana; in contrast to Kortello et al (2007), they attributed the change to elk switching habitats from open grasslands that mitigate predation risk from cougars to more structured habitats that mitigate predation risk from wolves, suggesting facilitation rather than any form of competition between top predators. Ruth et al (2011Ruth et al ( , 2015 found that cougars increased their use of structurally complex habitats after the reintroduction of wolves in Northern Yellowstone National Park, implying a reduction in the spatial attributes of the cougar's realized niche. Further, wolves killed three adult cougars and five kittens in Northern Yellowstone over the course of their study (Ruth 2004a(Ruth , 2015.…”

“…The SYE is a large undeveloped landscape where ungulate prey exhibit seasonal migrations (Sawyer et al 2005;Smith 2007;Nelson et al 2012;Elbroch et al 2013) and winter snows force wolves, cougars, and their prey to share lower elevations in late winter (Kortello et al 2007;Ruth et al 2011;Elbroch et al 2013). Evidence for competition between the two species implies that ongoing competition with wolves limits the realized niche of cougars.…”

Human-caused mortality influences spatial population dynamics: Pumas in landscapes with varying mortality risks

“…In the first 3 years of Garnet research (1997)(1998)(1999)(2000), pumas were heavily hunted throughout the study area, but in subsequent years (2001)(2002)(2003)(2004)(2005)(2006) hunting was restricted (Robinson and DeSimone, 2011). However, human-induced mortality remained relatively high over all years of Garnet research compared to the NGYE (Montana Fish, Wildlife and Parks hunt reports 1988-2007(DeSimone and Semmens, 2005;Ruth et al, 2011). We hypothesized that after puma hunting was restricted in the Garnet area the population's per capita contribution to the region would increase in part due to higher levels of dispersal into surrounding subpopulations.…”

Ecology and predator associations of the northern quoll (Dasyurus hallucatus) in the Pilbara

“…For example, individuals in a population are often forced to move due to natural dispersal events (Ruth et al 2011) or dispersal driven by high densities above carrying capacity (Benson and Chamberlain 2007). When an animal leaves an area (a source) it may disperse into a sink, which is a habitat of lower quality or of apparent high quality, but nonetheless associated with low survival rates (Andreasen et al 2012;Ruth et al 2011). Differences between source and sink habitats are especially evident in areas where mortality risk occurs in pulses, such as hunting seasons, allowing influx of individuals during the off-season.…”