Responses to future climates and conservation
The four cold-adapted bumblebees will dramatically shrink their ranges
as the distribution models unanimously predicted negative responses to
future climate change, despite their different geography and different
subgenera, thus fulfilling our hypothesis H1. The severe range
contractions predicted for the 2070s are particularly alarming as these
bumblebees are already enlisted in categories of extinction risk from
what had been observed in recent times (Nieto et al. 2014, Quaranta et
al. 2018) and our study shows that future climate dynamics will add up
to the current negative trends and threats. Responses as these are
expected and observed in a range of cold-adapted insects (Koot et al.
2022) and, to some extent, also on endotherms organisms in the same
contexts (de Gabriel Hernando et al. 2021, Brambilla et al. 2022),
making it very likely that H1 is a general rule for animals of cold
areas.
The severe future range shrinkage will likely be “concentric”, because
most future areas are predicted to occur within the current suitable
ones, while large surfaces will turn into inhospitable land. This result
supports the hypothesis H2 and adds evidence to what was observed in
previous studies in North America that clarified the determinant role of
changing temperature in causing range loss in bumblebees (Jackson et al.
2022). Similar results were obtained in alpine grasshoppers and are
concordant with other bumblebee species (Martínez-López et al. 2021,
Koot et al. 2022). Therefore, it is clear that the strong future
alteration of the current distribution pattern will further imperil the
lasting of these pollinators. Furthermore, our study demonstrated that
refugia areas estimated suitable by all scenarios will be of small size,
especially in the Apennines. Thus, the remaining patches will be
important refuges for the four bumblebee species studies, and
conservation measures should be strengthened there.
Some differences in shrinkage amount were detected among mountain
ranges, with the conditions in the Apennines being particularly harsh in
the future for the two studied bumblebees occurring there. For instance,B. mucidus , which occurs in all the three mountain ranges, will
decrease on the Apennines by a percentage almost twice those of the
other ranges. Likewise, the Apennines endemic B. konradini will
largely shrink its distribution. A similar scenario is expected for
other local elements of fauna and flora of this mountain range. The
Apennines range of two high-elevation butterflies will be considerably
small and even possibly disappear in future years (Sistri et al. 2022,
Bonifacino et al. 2022). Likewise, the area occupied by some Apennines
rare plants will considerably shrink (Di Musciano et al. 2020). We
suspect that differences in orientation, elevation range, general
climate and in diversity and extent of microhabitats among the three
massifs investigated here could explain these differential responses,
although without affecting the validity of H2. However, future research
efforts on understanding why the Apennines seems to be so subjected to
distribution loss in cold adapted species are clearly a priority, given
that this region will also pose important conservation challenges for
preserving its cold adapted fauna and flora.
Unfortunately, considering the unprecedented and fast rate of climate
change, it is difficult to estimate the efficacy of conservation
measures. Nevertheless, in a previous study, Biella et al. (2017)
suggested applying conservation measures for decreasing the non-climatic
stresses often associated with mountain environments, such as the
impacting tourist activities and the competition by domestic grazers.
Future, additional, efforts and studies could integrate physiological
aspects into conservation by valorizing potentially different response
abilities to heating in different populations, as previously proposed
for reptiles (Besson and Cree 2011). A critical consideration regards
refugia: it is surely a promising measure to protect and apply
mitigation strategies within areas that represent in-situ refugia
(shared by present and future scenarios) and also ex-situ ones (only in
future scenario) under a dynamic view of area conservation. Given that
climate refugia are key areas for the endurance of species facing
challenges by global change as these are likely to preserve suitable
environments (Brambilla et al. 2022), they must be considered as
priority areas for targeted conservation efforts. The fact that in
certain parts of the ranges a high proportion of refugia lies within the
Protected Area network could promote the implementation of conservation
measures.