Climate change vulnerability higher in arctic than alpine bumblebees

Arctic and alpine species are expected to be particularly vulnerable to climate change as they inhabit areas of extreme climates. To understand how such species may respond, we compared two groups of bumblebees that specialise in arctic (Alpinobombus) and alpine (Mendacibombus) biomes. These bumblebee species are all extreme cold specialists with similar ecological niches, making them good candidate species for comparison of how groups inhabiting different biomes may respond to climate change. Using an ensemble of species distribution models for eighteen bumblebee species (ten Mendacibombus; eight Alpinobombus), we estimated their current distributions using selected climate variables. The models were used to predict future distributions based on two future climate change scenarios for 2040-2060 and three dispersal scenarios. We found significant differences between the predicted relative area changes of the two groups under all combinations of climate change and dispersal scenarios. Alpinobombus species were consistently projected to have larger distribution declines, while the responses of Mendacibombus species were much more varied, with some Mendacibombus species projected to have distribution expansions provided that they are able to disperse to occupy new territory. From these results, we show that arctic species would be much more likely than alpine species to experience distribution declines under climate change.