Boreal caribou survival in a warming climate, Labrador, Canada 1996–2014
Isabelle Schmelzer, Keith P. Lewis, John D. Jacobs, Sara C. McCarthy
Abstract
Landscape disturbance exerts a strong influence on boreal caribou persistence. However, although anthropogenic disturbance in Labrador, Canada is low, caribou populations in this region are declining. Given that other mechanisms must be influencing these populations, we conducted a comprehensive analysis of hypotheses of the direct and indirect influences of climate on survival for 257 adult female boreal caribou from 5 populations over nearly two decades. Caribou survival was determined using known-fate models in MARK and an information-theoretic approach was used to evaluate multiple models of adult female caribou survival. Model sets examining monthly and annual changes in survival and the influence of a series of climatic conditions were constructed for each local population. Patterns of annual and within-year survival varied among populations. Moderate to high survival rates were documented for the majority of populations, but lower and more variable survival occurred in a population that had undergone a significant decline. Predation by wolves was the most important source of mortality, and seasonal incursions of 1000s of migratory caribou into boreal caribou wintering ranges may have led to apparent competition for populations with significant range overlap. Although the influence of climate on adult female boreal caribou survival was generally low, survival was weakly but positively related to snowfall, and negatively related to freezing rain during the fall. However, given that any variation in adult female survival has the potential to influence population trends, evaluating the influence of climatic factors on survival improves knowledge of the mechanisms underlying caribou population dynamics in a changing environment. These results, combined with the general declines in these populations, suggest that the disturbance-apparent competition paradigm which is the prominent hypothesis explaining declines in caribou populations in North America, requires a broader interpretation.