Elevation shifts and the fate of cold-adapted bumblebees
Average elevation of occurrence sites by the four bumblebees had considerably moved up, thus validating hypothesis H3: for all species the altitude shift so far occurred and predicted to happen in future is very high, although with varying estimates depending on the species. A unifying element is also the fact that the up-hill trend has started since the mid 1980s for all species, and will continue in future. Changes in elevation have been already observed in a number of bumblebees (Manino et al. 2007, Ornosa et al. 2017, Biella et al. 2017). The beginning of the elevational shift (the 1980s) is not surprising considering previous results on an alpine bumblebee (Biella et al. 2017) and that also thermophilic lowland bumblebees started expanding their range exactly from the 1980s (Biella et al. 2021a). This is confirmed by climatic data indicating that since the 1980s the warmest period of the last 800 years has started in the Northern Hemisphere (IPCC, Intergovernmental Panel on Climate, 2014), warming high elevation areas as twice as the global average during the 1980s and 1990s at a rate of 0.4 °C/decade (Pepin and Seidel 2005). In cold-adapted bumblebees occurring at high elevation, a continuous uphill shift of elevation range raises serious concerns for their fate, considering both the upper limit of the mountains and the reduction of land surface as elevation increases in pyramidally shaped mountains. These concerns are fuelled by the fact that future climate will particularly warm high elevation areas (Thuiller et al. 2005). Therefore, investigating and identifying possible microrefugia is a valuable option for further research that could eventually inform conservation practices, and for the fine-scale designation and management of priority areas.