Webinar - Demographic Responses of Threatened Woodland Caribou to Annual Variation in Meteorological and Phenological Conditions

Climate change is expected to increasingly impact populations of woodland caribou and much focus has been placed on how a warming climate has facilitated the northward expansion of apparent competitors (e.g., white-tailed deer) and novel predators (e.g., coyotes). Climate change, however, may also exert effects on caribou populations that are not mediated by predation. Here, we used data from 21 populations in western Canada to assess the demographic response of woodland caribou to annual variation in a suite of meteorological and phenological metrics. Recent research on other ungulate populations suggests that climatic variation may have minimal direct impact on low-density populations such as woodland caribou because per-capita resources may remain sufficient even in “bad” years. We tested this prediction by relating climatic variation to juvenile recruitment and adult female survival, two vital rates with high influence on caribou demography. Contrary to the low-density/low-impact prediction, we recorded relatively strong effects in both rates, though explained variation across all demographic models was low, suggesting that factors other than adverse climatic conditions had a greater influence on caribou demography during our monitoring period (1994–2015). In general, juvenile recruitment was more affected by variation in growing season conditions in the year prior to birth, responding positively to longer, more productive growing seasons and negatively to those that were warmer and drier. Adult female survival, in contrast, was more affected by winter conditions, responding negatively to colder and more variable winters during the monitoring year and up to three years prior. Given these unexpected results, we discuss alternative explanations as to why these woodland caribou populations did not conform to the low-density/low-impact prediction. The demographic effects we recorded have direct implications for caribou conservation, highlighting the increased relevance of recovery actions when adverse climatic conditions are more likely to negatively affect caribou demography.