Roles of maternal condition and predation in survival of juvenile Elk in Oregon

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...

Linking population performance to nutritional condition in an alpine ungulate

“…Vital rates that dictate population change are pregnancy, age of first reproduction, juvenile survival, and adult survival ( Gaillard et al 2000 )—all of which are linked to nutrition to varying degrees depending upon the species and the environment. For example, body fat was linked strongly to probability of pregnancy in caribou ( Gerhart et al 1996 ), moose ( Testa and Adams 1998 ), and to timing of breeding and thus parturition in elk ( Cook et al 2004 ; Johnson et al 2019 ). Tollefson et al (2010 ) observed that body fat predicted the probability of twinning in mule deer.…”

Puma population limitation and regulation: What matters in puma management?

“…There is no pretense that pumas limit their density so as not to reduce the abundance of their food supply. To the contrary, under certain circumstances pumas do so (Logan and Sweanor , Robinson et al , Johnson et al , Johnson et al ).…”

“…Puma predation is expected to influence ungulate populations in different ways depending upon environmental conditions and interactions of pumas with different prey and predator populations (Logan and Sweanor ; Robinson et al ; Kortello et al ; Elbroch et al , b ; Johnson et al ). Ultimately, the effect of puma predation on prey population growth will depend on the extents that predation is additive or compensatory.…”

“…Elk populations, where puma density is high, may be limited primarily by puma predation and less so by nutrition. In that circumstance puma predation can be partially compensatory and partially additive, and reduction in puma density might not result in increased recruitment (Johnson et al ).…”

Integrated Carnivore‐Ungulate Management: A Case Study in West‐Central Montana

“…Ungulate demography also needs to be evaluated to determine if changes in carnivore abundance result in changes in ungulate vital rates, and, ultimately, growth rate. If ungulate populations are limited by factors such as weather or habitat (Garrott et al 2003, Griffin et al 2011, Johnson et al 2019), or if predation is compensatory with other factors (Singer et al 2003, Garrott et al 2008), changes in carnivore populations may not result in changes in the key vital rates, such as recruitment, that drive ungulate population growth rate. The efficacy of integrated carnivore‐ungulate programs may be evaluated by monitoring these key ungulate vital rates and population growth pre‐ and post‐harvest treatment.…”