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.