North-westward range expansion of the bumblebeeBombus haematurusinto Central Europe is associated with warmer winters and niche conservatism

Abstract

Range expansions of naturally spreading species are crucial for understanding how species interact with the environment and build their niche. Here, we studied the bumblebee Bombus haematurus Kriechbaumer, 1870, a species historically distributed in the eastern Mediterranean area which has very recently started expanding northwards into Central Europe. After updating the global distribution of this species, we investigated if niche shifts took place during this range expansion between colonized and historical areas. In addition, we have explored which climatic factors have favoured the natural range expansion of the species. Our results indicated that Bombus haematurus has colonized large territories in 7 European countries outside the historical area in the period from the 1980s to 2018, a natural expansion over an area that equals the 20% of the historical distribution. In addition, this bumblebee performs generalism in flower visitation and habitat use, although a preference for forested areas emerges. The land-use associated with the species in the colonized areas is similar to the historical distribution, indicating that no major niche shifts occurred during the spread. Furthermore, the component of climate change that favoured this colonization is the warming of winter temperatures and similar warming rates took place during both overwintering and queen’s emergence phases. These findings document a case of natural range expansion due to environmental change rather than due to niche shifts, and specifically they indicate that warmer winters are playing a major role in the process of natural colonization of new areas.

Decline of parasitic and habitat-specialist species drives taxonomic, phylogenetic and functional homogenization of sub-alpine bumblebee communities

“…Using a replicated survey of historical (1940s-1960s) and recent (2012) bumblebee assemblages in subalpine habitats in Norway, we identified a change of bumblebee communities that is consistent with an effect of both climate and land-use change (Fourcade et al 2019). This is in accordance with studies that have documented two distinctive patterns of the impact of climate change on bumblebees: poleward (Kerr et al 2015, Biella et al 2020, and altitudinal (Ploquin et al 2013, Pyke et al 2016, Biella et al 2017) range shifts. Especially, our comparison with historical data revealed a shift towards more thermophilic species and a decline of the regional species pool by ca.…”