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Animals may partially overcome environmental constraints on fitness by behaviorally adjusting their exposure to costs and supplies of energy. Few studies, however, have linked spatiotemporal variation in the energy landscape to behaviorally mediated measures of performance that ostensibly influence individual fitness. We hypothesized that strength of selection by North American elk (Cervus elaphus) for areas that reduced costs of thermoregulation and activity, and increased access to high-quality forage, would influence four energetically mediated traits related to fitness: birth mass of young, nutritional condition of adult females at the onset of winter, change in nutritional condition of females between spring and winter, and neonatal survival. We used a biophysical model to map spatiotemporally explicit costs of thermoregulation and activity experienced by elk in a heterogeneous landscape. We then combined model predictions with data on forage characteristics, animal locations, nutritional condition, and mass and survival of young to evaluate behaviorally mediated effects of the energy landscape on fitness-related traits. During spring, when high-quality forage was abundant, female elk that consistently selected low-cost areas before parturition gave birth to larger young than less-selective individuals, and birth mass had a strong, positive influence on probability of survival. As forage quality declined during autumn, however, lactating females that consistently selected the highest quality forage available accrued more fat and entered winter in better condition than less-selective individuals. Results of our study highlight the importance of understanding the dynamic nature of energy landscapes experienced by free-ranging animals.

No abstract

Understanding bottom‐up, top‐down, and abiotic factors along with interactions that may influence additive or compensatory effects of predation on ungulate population growth has become increasingly important as carnivore assemblages, land management policies, and climate variability change across western North America. Recruitment and population trends of elk (Cervus canadensis) have been downward in the last 4 decades across the northern Rocky Mountains and Pacific Northwest, USA. In Oregon, changes in vegetation composition and land use practices occurred, cougar (Puma concolor) populations recovered from near‐extirpation, and black bear (Ursus americanus) populations increased. Our goal was to provide managers with insight into the influence of annual climatic variation, and bottom‐up and top‐down factors affecting recruitment of elk in Oregon. We conducted our research in southwestern (SW; Toketee and Steamboat) and northeastern (NE; Wenaha and Sled Springs) Oregon, which had similar predator assemblages but differed in patterns of juvenile recruitment, climate, cougar densities, and vegetative characteristics. We obtained monthly temperature and precipitation measures from Parameter‐elevation Regressions on Independent Slopes Model (PRISM) and estimates of normalized difference vegetation index (NDVI) for each study area to assess effects of climate and vegetation growth on elk vital rates. To evaluate the nutritional status of elk in each study area, we captured, aged, and radio‐collared adult female elk in SW (n = 69) in 2002–2005 and NE (n = 113) in 2001–2007. We repeatedly captured these elk in autumn (n = 232) and spring (n = 404) and measured ingesta‐free body fat (IFBF), mass, and pregnancy and lactation status. We fitted pregnant elk with vaginal implant transmitters (VITs) in spring and captured their neonates in SW (n = 46) and NE (n = 100). We placed expandable radio‐collars on these plus an additional 110 neonates in SW and 360 neonates in NE captured by hand or net‐gunning via helicopter and estimated their age at capture, birth mass from mass at capture, and sex. We monitored their fates and documented causes of mortality until 1 year of age. We estimated density of cougars by population reconstruction of captured (n = 96) and unmarked cougars killed (n = 27) and of black bears from DNA analysis of hair collected from snares. We found evidence in lactating females of nutritional limitations on all 4 study areas where IFBFautumn was below 12%, a threshold above which there are few nutritional limitations (9.8% [SE = 0.64%, n = 17] at Toketee, 7.9% [SE = 0.78%, n = 17] at Steamboat, 7.3% [SE = 0.33%, n = 46] at Sled Springs, and 8.9% [SE = 0.51%, n = 23] at Wenaha). In spring, of females known to have been lactating the previous autumn, 48% (SE = 3.3%, n = 56) had IFBFspring <2%, a level indicating severe nutritional limitations, compared to 20% (SE = 1.7%, n = 91) of those not lactating the previous autumn. These low levels of IFBFspring of lactating females likely resulted from a carry...