The harsh environmental conditions found in mountain ecosystems present special challenges to species living in such environments. Temperatures are low, solar radiation is high, winters are long, and summers are short. Animals living in the mountains have evolved strategies to deal with such unfavourable conditions. Climate change is expected to change these conditions substantially. Some mountain-adapted species will profit from the new circumstances, while the vast majority will experience negative consequences.
In this study we investigated how environmental and climatic factors affect the distribution and abundance of alpine marmots. One particular focus of our study was the influence of snow cover duration. If the snowpack melts too late in spring, vegetation is delayed, and marmots are not able to store enough fat reserves for the following winter. However, adequate snow cover is required during winter to insulate the burrow. Earlier snowpack cover therefore leads to higher winter survival.
In summer 2021 we surveyed marmots in the region of the Swiss National Park. We modelled the distribution and abundance of marmots as functions of environmental and climatic conditions. Besides snow cover we also analysed the influence of land cover, summer temperature, vegetation phenology and topography. We used existing environmental data alongside variables derived from Sentinel-2 satellite images.
The number of counted marmots is not only influenced by how suitable the habitat is, but also by how likely we were to detect a marmot during the survey. To correct for this observation bias, we used an approach called distance sampling, which explicitly models how the detection probability of a marmot decreases with distance from the observer. Correcting the number of counted marmots by the proportion that was missed produces accurate abundance estimates.
While the strongest explanation for marmot distribution was vegetation; areas with earlier snow melt were also inhabited by more marmots. However, the number of marmots was only weakly associated with the date of snow onset. Furthermore, Temperature and weather conditions during the survey affected the distance at which marmots could still be detected.
Climate change is changing the temperature and snow regime in the mountains. I will discuss the implications of our results in relation to climate projections over coming decades and if marmots may cope with future climatic conditions.