Macroecological perspectives on the competition between the native and invasive bumblebees in southern South America under climate change

Abstract

A handful of known bumble bee species (Bombus) have been transported worldwide and introduced in non-native regions for crop pollination, leading to long-lasting biological invasions. The introductions and invasions of European Bombus terrestris and, previously, of Bombus ruderatus in southern South America have been associated with sharp population declines of the giant Patagonian bumblebee, Bombus dahlbomii. We gathered a comprehensive database of occurrence records for B. dahlbomii, B. ruderatus, and B. terrestris from museums and citizen science sources. Multivariate bioclimatic niche analyses and species distribution models were used to determine the extent of climatic niche overlap between invasive and native species and the potential effects of current and future climatic scenarios on the distribution of these bumblebees. We found extensive pairwise niche overlap between the three bumble bee species, B. terrestris versus B. ruderatus (67%), B. terrestris versus B. dahlbomii (61%), and B. ruderatus versus B. dahlbomii (46%). Compared to its historical records, the current distribution of B. dahlbomii is narrowing and is expected to shrink even more under the most climatically pessimistic future scenario, while that of B. terrestris shows an extensive, still expanding distribution. However, the models show that in the case of a climatic pessimistic future scenario, B. terrestris will also slow down its expansion on the continent. Finally, we discuss the consequences of the large niche overlap between the introduced bumble bee species and endangered B. dahlbomii and the effect of climate change on these three species of bumble bees in South America.