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Woodland Caribou demographic data and range boundaries

Citation

DeMars, Craig et al. (2021), Woodland Caribou demographic data and range boundaries, Dryad, Dataset, https://doi.org/10.5061/dryad.stqjq2c3g

Abstract

As global climate change progresses, wildlife management will benefit from knowledge of demographic responses to climatic variation, particularly for species already endangered by other stressors. In Canada, climate change is expected to increasingly impact populations of threatened woodland caribou (Rangifer tarandus caribou) and much focus has been placed on how a warming climate has potentially facilitated the northward expansion of apparent competitors and novel predators. Climate change, however, may also exert more direct effects on caribou populations that are not mediated by predation. These effects include meteorological changes that influence resource availability and energy expenditure. Research on other ungulates suggests that climatic variation may have minimal impact on low-density populations such as woodland caribou because per-capita resources may remain sufficient even in “bad” years. We evaluated this prediction using demographic data from 21 populations in western Canada that were monitored for various intervals between 1994 and 2015. We specifically assessed whether juvenile recruitment and adult female survival were correlated with annual variation in meteorological metrics and plant phenology. Against expectations, we found that both vital rates appeared to be influenced by annual climatic variation. Juvenile recruitment was primarily correlated with variation in phenological conditions in the year prior to birth. Adult female survival was more strongly correlated with meteorological conditions and declined during colder, more variable winters. These responses may be influenced by the life history of woodland caribou, which reside in low-productivity refugia where small climatic changes may result in changes to resources that are sufficient to elicit strong demographic effects. Across all models, explained variation in vital rates was low, suggesting that other factors had greater influence on caribou demography. Nonetheless, given the declining trajectories of many woodland caribou populations, our results highlight the increased relevance of recovery actions when adverse climatic conditions are likely to negatively affect caribou demography.

Methods

Demographic data from woodland caribou were provided by the governments of Alberta, British Columbia, and Northwest Territories. Calves: adult female ratios (CAF) were estimated from aerial surveys conducted in March. These surveys recorded the total number of calves and adult females observed (mean = 147.3 adult females observed/caribou range/year [range: 11–1288]). CAF ratios were not adjusted to reflect the number of female calves to the total number of females across all age classes. Annual estimates of adult female survival (AVS) were derived from data collected from VHF- or GPS-collared adult females (≥2 years old; exact ages on capture are unknown) in each caribou population . For VHF-collared females, survival status was determined by aerial telemetry flights conducted 4–12 times per year, a monitoring frequency found to produce unbiased survival estimates.  Annual rates of AFS for each population were estimated using the Kaplan-Meier method in a staggered entry design.

Also provided is a shapefile depicting the range boundaries for the 21 subpopulations of woodland caribou used in the analyses. The data were also provided by the governments of Alberta, British Columbia, and Northwest Territories. 

Funding

British Columbia Oil and Gas Research and Innovation Society