Browsing by Author "Hebblewhite, Mark"

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Evaluating the summer landscapes of predation risk and forage quality for elk ( Cervus canadensis )
(Wiley, 2022-08) Paterson, J. Terrill; Proffitt, Kelly M.; DeCesare, Nicholas J.; Gude, Justin A.; Hebblewhite, Mark
The recovery of carnivore populations in North American has consequences for trophic interactions and population dynamics of prey. In addition to direct effects on prey populations through killing, predators can influence prey behavior by imposing the risk of predation. The mechanisms through which patterns of space use by predators are linked to behavioral response by prey and nonconsumptive effects on prey population dynamics are poorly understood. Our goal was to characterize population- and individual-level patterns of resource selection by elk (Cervus canadensis) in response to risk of wolves (Canis lupus) and mountain lions (Puma concolor) and evaluate potential nonconsumptive effects of these behavioral patterns. We tested the hypothesis that individual elk risk-avoidance behavior during summer would result in exposure to lower-quality forage and reduced body fat and pregnancy rates. First, we evaluated individuals' second-order and third-order resource selection with a used-available sampling design. At the population level, we found evidence for a positive relationship between second- and third-order selection and forage, and an interaction between forage quality and mountain lion risk such that the relative probability of use at low mountain lion risk increased with forage quality but decreased at high risk at both orders of selection. We found no evidence of a population-level trade-off between forage quality and wolf risk. However, we found substantial among-individual heterogeneity in resource selection patterns such that population-level patterns were potentially misleading. We found no evidence that the diversity of individual resource selection patterns varied predictably with available resources, or that patterns of individual risk-related resource selection translated into biologically meaningful changes in body fat or pregnancy rates. Our work highlights the importance of evaluating individual responses to predation risk and predator hunting technique when assessing responses to predators and suggests nonconsumptive effects are not operating at a population scale in this system.
Forest structure provides the income for reproductive success in a southern population of Canada lynx
(2018-02) Kosterman, Megan K.; Squires, John R.; Holbrook, Joseph D.; Pletscher, Daniel H.; Hebblewhite, Mark
Understanding intrinsic and extrinsic drivers of reproductive success is central to advancing animal ecology and characterizing critical habitat. Unfortunately, much of the work examining drivers of reproductive success is biased toward particular groups of organisms (e.g., colonial birds, large herbivores, capital breeders). Long-lived mammalian carnivores that are of conservation concern, solitary, and territorial present an excellent situation to examine intrinsic and extrinsic drivers of reproductive success, yet they have received little attention. Here, we used a Canada lynx (Lynx canadensis) dataset, from the southern periphery of their range, to determine if reproductive success in a solitary carnivore was consistent with capital or income breeding. We radio-marked and monitored 36 female Canada lynx for 98 lynx years. We evaluated how maternal characteristics and indices of food supply (via forest structure) in core areas influenced variation in body condition and reproductive success. We characterized body condition as mass/length and reproductive success as whether a female produced a litter of kittens for a given breeding season. Consistent with life-history theory, we documented a positive effect of maternal age on body condition and reproductive success. In contrast to predictions of capital breeding, we observed no effect of pre-pregnancy body condition on reproductive success in Canada lynx. However, we demonstrated statistical effects of forest structure on reproductive success in Canada lynx, consistent with predictions of income breeding. The forest characteristics that defined high success included (1) abundant and connected mature forest and (2) intermediate amounts of small-diameter regenerating forest. These attributes are consistent with providing abundant, temporally stable, and accessible prey resources (i.e., snowshoe hares; Lepus americanus) for lynx and reinforce the bottom-up mechanisms influencing Canada lynx populations. Collectively, our results suggest that lynx on the southern range periphery exhibit an income breeding strategy and that forest structure supplies the income important for successful reproduction. More broadly, our insights advance the understanding of carnivore ecology and serve as an important example on integrating long-term field studies with ecological theory to advance landscape management.
Neonatal mortality of elk driven by climate, predator phenology and predator community composition
(2011-05) Griffin, K.; Hebblewhite, Mark; Robinson, H.; Zager, Peter; Barber-Meyer, S.; Christianson, David A.; Creel, Scott; Harris, N.; Hurley, M.; Jackson, D.
Understanding the interaction among predators and between predation and climate is critical to understanding the mechanisms for compensatory mortality. We used data from 1999 radio-marked neonatal elk (Cervus elaphus) calves from 12 populations in the north-western United States to test for effects of predation on neonatal survival, and whether predation interacted with climate to render mortality compensatory. Weibull survival models with a random effect for each population were fit as a function of the number of predator species in a community (3–5), seven indices of climatic variability, sex, birth date, birth weight, and all interactions between climate and predators. Cumulative incidence functions (CIF) were used to test whether the effects of individual species of predators were additive or compensatory. Neonatal elk survival to 3 months declined following hotter previous summers and increased with higher May precipitation, especially in areas with wolves and/or grizzly bears. Mortality hazards were significantly lower in systems with only coyotes (Canis latrans), cougars (Puma concolor) and black bears (Ursus americanus) compared to higher mortality hazards experienced with gray wolves (Canis lupus) and grizzly bears (Ursus horribilis). In systems with wolves and grizzly bears, mortality by cougars decreased, and predation by bears was the dominant cause of neonatal mortality. Only bear predation appeared additive and occurred earlier than other predators, which may render later mortality by other predators compensatory as calves age. Wolf predation was low and most likely a compensatory source of mortality for neonatal elk calves. Functional redundancy and interspecific competition among predators may combine with the effects of climate on vulnerability to predation to drive compensatory mortality of neonatal elk calves. The exception was the evidence for additive bear predation. These results suggest that effects of predation by recovering wolves on neonatal elk survival, a contentious issue for management of elk populations, may be less important than the composition of the predator community. Future studies would benefit by synthesizing overwinter calf and adult-survival data sets, ideally from experimental studies, to test the roles of predation in annual compensatory and additive mortality of elk.