Effects of land-use intensification and environmental stressors on intraspecific functional traits variability in bumblebees

Abstract

Landscape anthropization replaces natural areas with agricultural or urban covers, leading to land-use intensification. This worldwide phenomenon affects biodiversity, but little is known about the effects on the intraspecific variation of functional traits related to ecosystem services. By combining field data collection, remote sensing and land cover analysis we investigated how land use intensification affects functional traits in two bumblebee species. Namely, the impact of different land use cover (i.e., semi-natural, urban, and agricultural) and of multiple biotic and abiotic stressors (i.e., temperature, resource availability, and air pollutants) was investigated. Along a gradient of landscape anthropization, we sampled populations of two European bumblebee species (Bombus terrestris and B. pascuorum) at 37 sites in Northern Italy. Through geometric morphometrics we investigated the variation of morphological traits related to flight performance (i.e., wing centroid size and shape and size fluctuating asymmetry FA), previously used as indicators of stress during insect development. Our results point out an idiosyncratic response of the two species to landscape anthropization. Smaller individuals of B. pascuorum were observed in response to increased impervious cover and temperature. No similar patterns were noticed in B. terrestris, which was characterized by larger individuals in response to floral resource availability. Wing size FA was positively associated with warmer temperatures and increased levels of NO2 only in B. terrestris. Overall, this study found taxon-specific functional trait variation at the intraspecific level in syntopic organisms, expanding our understanding about the effects of land-use intensification on the ecological activity of pollinator model species.