Differing effects of climate change on wild bee nesting groups across Europe

Wild bees are declining globally, as well as in Europe, and environmental drivers responsible for it are mainly related to climate change. The complex network of environmental effects on groups of bees, mediated by species traits is still not entirely known, especially regarding nesting traits. Therefore, this study assessed the responses of an assemblage of wild bees, according to nesting strategy, to climate change predictors and their distributions, through time. Seventy species were selected, divided into below-ground nesting bees (35) and above-ground nesting bees (35). A stacked species ensemble modelling approach was used, composed of maximum entropy, generalized linear models and random forest algorithms. Furthermore, two Shared Socioeconomic Pathways (SSPs) scenarios were used: SSP 2–4.5 and SSP 3–7.0. Climate predictors consisted of temperature and precipitation variables, selected through multicollinearity analysis by Variance Inflation Factor (VIF). The results showed that temperature variables were more important than precipitation, shown by higher mean variable importance values. Response curves showed that irrespective of nesting group, wild bees responded negatively to increased temperature and precipitation. Multivariate Environmental Similarity Surface (MESS) and uncertainty analysis showed reduced extrapolation, being mostly limited to Southern and Eastern Europe, although it differed by nesting group. Habitat suitability declined more steeply with time and SSP scenarios. Below-ground nesters had higher suitability losses, especially in Southern Europe, worsening at SSP3–7.0. Above-ground nesters gained more suitable habitat, in Eastern and Northern Europe. These findings demonstrate the differences in response of wild bee species to climate change, mediated by species traits and help further assessment of trends in decline of wild bees in Europe.