The Community Ecology of Large Carnivores in the Mountain West (hosted by TWS)

Symposium
ROOM: RSCC, D6
SESSION NUMBER: 8168
 
Inhabiting the apex predator position in the trophic systems in which they reside, large carnivores are integral to the function of ecosystems. These predators exert both consumptive and non-consumptive effects in their prey with consequences that can cascade through trophic systems. Furthermore, the competition between and among large carnivores and mesocarnivores shapes the carnivore guild. Concurrently, large carnivores have shown a capacity to threaten the security and private property of many people that share their landscape with these species. In the dynamic 21st century, over ¾ of the remaining species of large carnivore have declining population trajectories. Thus, there are a number of abiotic, biotic, and anthropogenic dynamics that are influential to the community ecology of large carnivores. Though relevant around the world, the Mountain West of the United States is a particularly important region for research on these topics given a number of high profile large carnivore restoration efforts and ongoing large carnivore range expansion. This symposium outlines the community ecology of the systems in which large carnivores reside in the Mountain West. Topics of particular focus will include the: 1) trophic linkages among large carnivores and other species in these Mountain West systems, 2) community ecology of multi-carnivore guilds, 3) spatial modeling of hot spots of human-carnivore conflict, and 4) behavioral plasticity of carnivores in response to human activity, among others. This symposium intends to pave a clear pathway for the development of ecological theory and the creation of progressive management and conservation practice relating to large carnivores.

8:00AM A Tendency to Simplify Complex Systems
  Robert Montgomery
Predation is a fundamental force exerting strong selective pressure on prey populations. Predators not only kill prey, triggering lethal effects, but also hunt prey which can induce risk effects. Foundational research has documented the importance of risk effects in predator-prey systems of arthropods, fish, birds, and rodents, among others. Within systems of fierce carnivores hunting mobile and elusive ungulate prey however, risk effects research has only expanded in the last 20 years. Presently, the degree to which this research mirrors the complexity of carnivore-ungulate trophic systems has been questioned. The objective of our analysis was to determine the extent to which experimental designs among risk effects research in carnivore-ungulate systems consider the trophic interactions of multiple carnivore predators and multiple ungulate prey. Thus, we synthesized carnivore-ungulate risk effects literature to quantify the tendency for these studies to be multispecies in design. Among the 170 studies that we reviewed, we found that on average just 1.26 (range = 1 to 5) carnivore species and 1.60 (range = 1 to 11) ungulate species were considered per study. Furthermore, 63% (n =107 of 170) of the studies featured single predator – single prey research designs. These results contrast with the fact that all but one of the 82 carnivore-ungulate systems in this literature had multiple species of resident carnivores and/or ungulates. By in large, we detected a tendency to simplify complex systems. We relate these observations to the role of simplicity as: i) an underlying value of science (i.e., Occam’s razor), ii) a cornerstone of predator-prey theory (e.g., Lotka-Volterra equations), and iii) part of the origins of risk effects research (i.e., experimental systems). Finally, we ground our discussion in the implications of this research for the conservation of carnivores and ungulates in the dynamic 21st century.
8:20AM Relationship between Amount of Suitable Habitat and Genetics in a Wide-Ranging Large Carnivore
  Justin Dellinger
Co-considering the ecology (e.g., habitat use) and evolution (e.g., population genetic structure and diversity) of a species can increase understanding of current population status and inform future management practices. Previous analyses indicate mountain lions (Puma concolor) in California are genetically structured and exhibit extreme variation in population genetic diversity. Although human development may have fragmented gene flow, we hypothesized the remaining habitat available would affect the evolution and population genetic diversity of each population. Results from regression analyses indicate that amount of suitable habitat, determined via a resource selection function derived using >800,000 location fixes from 225 radio-collared mountain lions, is strongly and positively associated with population genetic diversity, notably effective population size. Protected suitable habitat, not just the amount of habitat, had a more apparent positive impact on population genetic diversity. Our asymptotic results suggest that contiguous habitat of ≥10,000 km2 may be expansive enough to alleviate the measureable negative evolutionary effects of genetic drift and inbreeding, allowing mountain lion populations to maintain suitable effective population sizes. Five of the nine geographic–genetic mountain lion populations in California fell below this habitat threshold and two of those five populations lack connectivity to nearby populations. Enhancing the ecological conditions via protection of more suitable habitat and facilitating positive evolutionary processes via increased connectivity (e.g., road crossing structures) might ensure these small and/or isolated populations persist into the future. Our results demonstrate the amount and status of suitable habitat influence the evolutionary potential of large carnivores. Our results will inform conservation genetics efforts for mountain lions and other top predator populations, aiding in long-term population viability.
8:40AM Artificial Night Light Creates a Predator Buffet
  Mark Ditmer
Artificial light at night (ALAN) is increasingly recognized as important sources of environmental disturbance that degrade wildlife habitat conditions and influences the biology and ecology of numerous species. Despite globally elevated levels of sensory pollution, quantifying the effects of ANLN on wildlife ecology at a macro-scale has received little attention. We investigated how ALAN influenced predator-prey relationships using spatially-explicit estimates of ALAN and data from GPS-collared cougars (Puma concolor; n = 117) and their primary prey, mule deer (Odocoileus hemionus; n = 486), and 1,650 cougar-killed mule deer cache sites in the Great Basin. We hypothesized that ALAN may act as a predator shield (regions with higher levels of ALAN provide abundant forage without fear of predation). Alternatively, if cougars seek out this high density of prey and kill without regard to ALAN levels it may create a “predator buffet” (unlimited buffet), or cougars may only use the darkest areas within the urban-interface to move and hunt (limited buffet). We used resource selection functions, generalized additive models, and integrated step-selection functions to assess how ALAN and natural habitat features influenced areas where cougars killed the most deer, activity periods, and movement and resource selection patterns. Results support the “limited predator buffet” hypothesis; mule deer kill sites were located at the boundaries of elevated ALAN levels, but in the relatively darkest locations, and deer in the urban-interface foraged longer in areas with higher NDVI and selected for areas with elevated light levels. Cougars in the darker regions killed mule deer with typical habitat characteristics (rugged, near habitat edges), while the opposite was true for kill sites in the high ALAN regions. Determining how ALAN influences the ecology of species at fine and macro-scales is critical for the future management and conservation of species encountering this growing source of environmental pollution.
9:00AM The Challenges of Managing Large Carnivores in Human-Dominated Landscapes: Grizzly Bear Recovery As a Case Study
  Hilary Cooley
The USFWS listed grizzly bears as a Threatened species in the lower-48 States in 1975 and subsequently designated six recovery zones. Due to the success of conservation efforts and collaboration among a variety of stakeholders, two of these populations (Greater Yellowstone Ecosystem, Northern Continental Divide Ecosystem) have achieved recovery goals and the USFWS is working towards delisting. Conservation success, however, brings significant management challenges as both populations are expanding into human-dominated landscapes. We review population status, management issues, and litigation challenges. We also present updates on recovery and management in the small Cabinet-Yaak and Selkirk Ecosystems and the currently unoccupied North Cascades and Bitterroot Ecosystems.
9:20AM Impacts of Recolonizing Black Bears on Cougar Predation Behavior
  Kristin Engebretsen
In Nevada’s Great Basin, cougars (Puma concolor) have been thriving as the apex predator without competition from other carnivores for approximately 80 years, due to the extirpation of black bears (Ursus americanus) and grizzly bears (Ursus arctos) from the region by the 1930s. However, recent conservation efforts have allowed black bears to begin successfully recolonizing their historic range in the western Great Basin. Data from ongoing studies focused on black bear recovery and cougar population demographics throughout the eastern Sierra Nevada and western Great Basin Desert indicate that black bears frequently visit and kleptoparasitize prey resources from cougars. These preliminary findings suggest that there may be differences in bear and cougar interactions across mountain ranges as black bears recolonize the region, but the impacts of bear density and scavenging pressure on cougar foraging behavior have not been fully explored. Using data from kill site investigations collected from 30 GPS-collared cougars between 2009 and 2017, we show the effects that the recovery and increasing population of recolonizing black bears have on cougar kill rates and prey selection. We used general linear mixed models to determine whether changes in bear density and scavenging pressure at kill sites impact cougar kill rate or prey selection across multiple mountain ranges, both with and without recolonizing bears. Understanding to what extent black bears usurp cougar kills will reveal the impact that black bear scavenging has on cougar predation of mule deer and other prey species and, thus, aid in managing a healthy balance between predators and prey. Our research will combine data from long-term studies of two large carnivores outside protected areas to improve our understanding of predator community dynamics with recolonizing large carnivores. Subsequently, our results should guide the development of management plans for multi-predator multi-prey systems in working landscapes across the Mountain West.
09:40AM Break
10:10AM The Role of Cougar Population Growth in the Use of Residential Areas and Interactions with People
  Brian Kertson
The presence of large carnivores close to people poses unique challenges for wildlife managers working to maintain fully functioning ecosystems while simultaneously minimizing potential risks to public safety and private property. In western North America, cougar (Puma concolor) use of residential areas is relatively commonplace and may lead to undesirable interactions with people. Wildlife managers often assume that cougar population growth translates into greater use of residential environments and more interactions, but direct evaluation of this assumption has not occurred. We used single-sex Leslie matrices, utilization distributions, confirmed interaction reports, and a two-stage hurdle model to investigate the effects of population trajectory on cougar use of residential areas and interactions with people in western Washington during a period of population stability (2004-2008; λ̂ = 1.00) and growth (2013-2017; λ̂ = 1.27). We predicted that use of residential areas and interaction levels would be greater for individual demographic classes and the population as a whole during the period of growth. Contrary to our prediction, we did not detect meaningful differences in cougar presence in residential areas and the number of interactions between time periods. We also documented consistent space use patterns by individual demographic classes as males and subadults were more likely to use residential areas than females and adults while females and subadults used residential portions of the landscape more intensively than males and adults. Our results suggest a growing cougar population does not necessarily translate into greater proximity to people and more interactions. Consequently, management strategies that rely exclusively on reducing population growth to reduce conflicts may not achieve their desired objectives. Cougar management in wildland-urban landscapes would likely benefit from an interdisciplinary approach that incorporates the management of prey, outreach to improve animal husbandry practices, and land use planning that concentrates residential development and increases connectivity.
10:30AM Carnivore Sympatry in Core Habitat of Black Bears
  Remington Moll
In carnivore guilds, larger and more dominant species can shape community dynamics by influencing the behavior of smaller, subordinate carnivores that seek to avoid exploitative and/or interference competition. However, not all subordinate carnivores will respond in the same way to dominant carnivores. Thus, intra-guild spatial interactions in carnivore communities might proceed along complex pathways governed by the dominant species’ influence over subordinates. We examined the potential for these dynamics among sympatric carnivores in western Nevada. Specifically, we evaluated the top-down influence of black bears (Ursus americanus) over a mesocarnivore community consisting of coyotes (Canis latrans), bobcats (Lynx rufus), gray foxes (Urocyon cinereoargenteus), and kit foxes (Vulpes macrotis). Mountain lions (Puma concolor) occur in this system at lower densities than black bears, the most common dominant carnivore. We evaluated whether mesocarnivore community composition varied across the core habitat of black bears by combining a resource selection function, fit to GPS data from 30 black bears, with occupancy models, fit to data from a large camera trapping grid. We found that the carnivore community in the core areas of black bears tended to be composed of bobcats and both fox species, while in areas lacking bears, fewer bobcats were detected but coyotes and foxes were common. These results suggest black bears mediate the sympatry of the two medium-bodied subordinate carnivores (coyotes and bobcats), but do not directly affect the two smaller-bodied carnivores (foxes). Thus, exploitative and/or interference competition between black bears and coyotes may be an important determinant of bobcat occupancy in our study system. Further, there was no evidence that black bears “released” smaller-bodied carnivores (foxes), perhaps because one medium-bodied mesocarnivore was replaced by another with increasing black bear use. Overall, this study highlights the important role black bears play in carnivore community dynamics in the American west.
10:50AM The Tangled Web We Weave: Incorporating Human Influence into Predator-Prey Dynamics
  Kristin Barker
Large carnivores are recovering in many landscapes where the human footprint is simultaneously expanding. Some studies have found that large carnivores strongly avoid human activity, whereas others highlight the adaptability of carnivores to human disturbance. Because carnivore response to humans has received little mechanistic study, there is significant uncertainty about how predator-prey interactions – and their associated ecosystem services and management considerations – will play out in human-dominated areas. For instance, humans may create refuge areas where prey populations flourish and can cause management conflicts, or humans may create areas where resource subsidies congregate prey and draw increased predator encounters. To improve understanding of predator-prey interactions in anthropogenic landscapes, we examined wolf (Canis lupus) movements and kill sites in Jackson Hole, Wyoming, where approximately 11,000 elk (Cervus canadensis) winter across a land use gradient ranging from a busy townsite to seasonally-closed wilderness areas. We used GPS collar data from more than 30 wolves in 8 packs collected over 10 winters along with prey distribution and environmental data to model wolf resource selection in the absence of human influence. Then, to test whether and how human influence alters wolf distribution, we compared this model’s predictions with other models that included up to 4 anthropogenic predictors: motorized use areas, presence of humans (i.e., non-motorized use areas), structural developments, and activity associated with supplemental ungulate feeding. We also assessed the influence of human activity on wolf predation by modeling wolf kill site selection using data collected during winter 2019. Finally, we compared results of the resource selection and kill site selection models to determine whether humans had similar effects on wolf distributions and predation events. Our work sheds new light on mechanisms governing predator-prey interactions in anthropogenic areas while providing relevant information to managers working in and around the wildlife-human interface.
11:10AM Timescapes of Fear: Sympatric Ungulates Change Spatiotemporal Activity in Response to Contrasting Predation Risk from Humans and Apex Predators
  Carolyn Shores
A growing body of research suggests that apex carnivores can regulate ecosystems through top-down trophic cascades. Much of this research has come from studies in relatively natural landscapes with low impact from humans, yet in large parts of the world apex carnivores coexist with prey in human-modified ecosystems where prey are also hunted by people. The effects of large carnivores on prey behavior in these ecosystems, where prey are forced to choose between minimizing risk from human hunters or carnivores, is not well understood. We investigated how human hunting influences prey behavior and to what extent it alters the behaviorally-mediated effects of large carnivores in a multi-predator, multi-prey ecosystem in northeastern Washington state, USA. Specifically, we used remote cameras to compare the habitat associations and diel activity patterns of mule deer (Odocoileus hemionus)and white-tailed deer (O. virginianus) during hunting and non-hunting seasons in an ecosystem with multiple large carnivores (wolves, Canis lupus; cougars, Puma concolor). Habitat features considered were distance to roads, terrain steepness, and forest cover. We found that mule deer changed their activity patterns and habitat associations during hunting seasons more than white-tailed deer, and altered their habitat use in ways that may make them more vulnerable to predation from large carnivores. Both deer species increased nocturnal activity during hunting seasons, but only mule deer decreased diurnal activity at the same time. Neither deer species responded to cougars, whereas mule deer avoided and white-tailed deer were associated with wolves. Our results suggest that human hunting of prey may temporarily cancel out behaviorally-mediated top-down effects of large carnivores, and that changes in prey behavior to avoid humans may increase predation risk from large carnivores for some prey species.
11:30AM How the Fear of Humans Shapes Mountain Lion Behavior and Their Associated Food Web in the Santa Cruz Mountains of California
  Chris Wilmers
The landscape of fear can have profound impacts on the behavior and ecology of animals, but as yet, there have been no experiments testing how large carnivores respond to fear and how this impacts lower trophic levels. Here we present the results of experiments designed to test whether mountain lions fear humans and how these fear responses impact other food web members. Through these experiments and associated observations, we show that fear of people impacts how mountain lions move on the landscape, how many calories they burn, how many deer they kill, mesopredator behavior, rodent home range sizes and the architecture of trees.

 
Organizers: Robert Montgomery, Pat Jackson, Joshua Millspaugh
 

Symposium
Location: Reno-Sparks CC Date: October 1, 2019 Time: 8:00 am - 11:50 am