Delayed phenology and reduced fitness associated with climate change in a wild hibernator

Abstract

The most commonly reported ecological effects of climate change are shifts in phenologies, in particular of warmer spring temperatures leading to earlier timing of key events. Among animals, however, these reports have been heavily biased towards avian phenologies, whereas we still know comparatively little about other seasonal adaptations, such as mammalian hibernation. Here we show a significant delay (0.47 days per year, over a 20-year period) in the hibernation emergence date of adult females in a wild population of Columbian ground squirrels in Alberta, Canada. This finding was related to the climatic conditions at our study location: owing to within-individual phenotypic plasticity, females emerged later during years of lower spring temperature and delayed snowmelt. Although there has not been a significant annual trend in spring temperature, the date of snowmelt has become progressively later owing to an increasing prevalence of late-season snowstorms. Importantly, years of later emergence were also associated with decreased individual fitness. There has consequently been a decline in mean fitness (that is, population growth rate) across the past two decades. Our results show that plastic responses to climate change may be driven by climatic trends other than increasing temperature, and may be associated with declines in individual fitness and, hence, population viability.

Fitness implications of seasonal climate variation in Columbian ground squirrels

“…However, delays in phenology may also produce detrimental fitness consequences (Lane et al. 2012; Chambers et al. 2013).…”

“…2012). On the east side of the Rocky Mountains, habitats have not exhibited the usual temperate zone pattern of warmer spring temperatures.…”

“…Rather, over a 20‐year period, spring temperatures declined by about 2°C and snowmelt was delayed by about 57 days, partly owing to later and more frequent spring snowstorms (Lane et al. 2012). However, conditions in spring are unlikely to be the only climate influence, because this species has a relatively short 3‐month active season, during which both reproduction and fat storage for the subsequent 9 months of hibernation must occur (Young 1990; Dobson et al.…”

“…Such climate influences could act independently or synergistically with the influence of spring snowfall on emergence from hibernation and the timing of breeding for adult females (Lane et al. 2012). Our ability to track the fitness of every female in our population of this sedentary species makes it ideal for investigating the potential effects of climate variables on fitness, during and outside of the usual spring emergence/breeding period.…”

“…We used a “sliding window” search procedure (Lane et al. 2012; Mihoub et al. 2012) to identify relevant periods of change during the year in both climate and fitness.…”