Drastic shifts in the Belgian bumblebee community over the last century

Bumblebees are undergoing strong declines in Europe caused by habitat loss and fragmentation, agricultural intensification, and climate change. Long-term records are necessary to estimate population trends precisely and to propose appropriate mitigation strategies. Based on an original database of 173,788 specimens from museum collections, scientific monitoring, and opportunistic citizen data from 1810 to 2016, we compared changes in species richness and area of occupancy of Belgian bumblebee species through three time-periods (1910-1930, 1970-1989, and 1990-2016). We also assessed if the observed trends are related to species-specific ecological traits and spatial scales (local, regional and national). Overall, species richness decreased over the last century in Belgium, but some regions retained relatively species-rich communities. A strong shift in community composition occurred. Three species remained among the top five in terms of species occurrence (area of occupancy) between the three time-periods (B. pascuorum, B. lapidarius, and B. pratorum), but several species that were once widespread declined drastically (B. muscorum, B. humilis, B. ruderatus, and B. veteranus), while a few species increased their distribution (e.g. B. hypnorum and B. terrestris). Habitat preferences significantly explained the observed trends, with declining species preferring open habitats and increasing species preferring wooded habitats.