Demographic responses of a threatened, low-density ungulate to annual variation in meteorological and phenological conditions

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.

Effects of climate variability on the demography of wild geladas

“…However, there may also be more opaque, indirect explanations for these lagged effects. Although 1‐year lagged effects have only been shown in primates due to rainfall and the El Niño climate oscillation ( Brachyteles hypoxanthus and Lagothrix lagothricha : Wiederholt & Post, 2011 ), lagged effects from temperature have been found in a variety of montane and grassland mammals including on population growth in American bison ( Bison bison : Koons et al, 2015 ) and adult female survival and juvenile recruitment in woodland caribou ( Rangifer tarandus caribou : DeMars et al, 2021 ). Willisch et al ( 2013 ) found that higher winter air temperatures corresponded to decreased survival in adult males and yearlings in alpine chamois ( Rupicapra rupicapra ).…”

Incorporating mechanism into conservation actions in an age of multiple and emerging threats: The case of boreal caribou

“…Potential impacts are not restricted to winter. Juvenile recruitment has been negatively correlated to warmer growing seasons that lead to early plant senescence in autumn (DeMars et al, 2021), an important period of resource acquisition for capital breeders such as caribou. Although current impacts from these direct mechanisms are likely secondary to the other more indirect mechanisms previously discussed (e.g., apparent competition), there is considerable uncertainty as to how the magnitude of these direct impacts may change as climate change progresses (DeMars et al, 2021).…”

Southern Europe is becoming favourable for African birds: anticipating the establishment of a new species

“…According to several studies, however, climate appears to be the most relevant factor for several taxa at large scales [2][3][4][5]. In recent decades, it has been demonstrated that the global climate is becoming warmer [6], with widespread effects on biological systems [7][8][9][10]. This recent climate change has already affected the distribution of many species [11][12][13][14] and is modifying the margins of their distributions over short periods of time [15][16][17].…”