A mechanistic model of endotherm hibernation applied to the endangered Mountain Pygmy Possum under climate change

Hibernation is an important energy- and water-conserving strategy in many endotherms. Global warming is changing species’ phenology and hibernation patterns, but whether such changes are beneficial or harmful depends on the species’ life-history traits, physiology, morphology and behaviour. Nonetheless, large decreases in the duration of hibernation will likely be detrimental to hibernators because they typically must contend with greater energy and water demands, as well as increased interaction with competitors and/or predators. Mechanistic niche models can be used to make strong inferences on such responses by explicitly quantifying the consequences of changed hibernation patterns for energy and water requirements. However, they are rarely applied in this context. Here we developed a general approach to this problem by adapting the endotherm biophysical model of the NicheMapR package. We then used this approach to assess the effect of climate change on the critically endangered mountain pygmy possum (Burramys parvus). Specifically, we contrasted 2010 conditions to two future climate-change scenarios (2°C or 4°C of average warming) for: (i) patterns in the energetic and hydric advantages of hibernation and changes in hibernation; (ii) the consequences of these hibernation changes for the species’ energy and water requirements; and (iii) the areas across southeast Australia that could continue to support hibernation. We project a 11-43% reduction in current hibernation hours for the mountain pygmy possum under climate change. This increase in activity caused the energy and water required for physiological maintenance to rise by 4-21% and 10-34%, respectively. Individuals would need to consume between 77-110% more energy and 48-72% more water annually and if they did not hibernate. This energetic and hydric advantage of hibernation declined with climate change at all four sites. Currently occupied areas and Tasmania were found to be the only areas in Australia suitable for hibernation under a 4° warming scenario. Our results indicate that climate change will have a profound impact on the duration and patterns of hibernation, a key survival strategy, for the mountain pygmy possum. Our framework for analysing changing hibernation patterns provides a new and general way to test the vulnerability and adaptability of endotherms facing global change.