The Distribution of Wild Bee Species Along a Latitudinal Gradient in Northern Europe Depends on Their Flower Preferences

Aim: The functional diversity of bees contribute to the maintenance of plant biodiversity because different species of wild bees prefer and pollinate different plants. Many bees, in particular species with narrow flower preferences or specialised habitat requirements, are threatened by landscape homogenisation and climate change. Nonetheless, we still lack an understanding of large-scale impacts of anthropogenic stressors on the distribution of wild bee species with different flower preferences. Location: Northern Europe: Norway, Denmark and Germany. Methods: We combine a dataset comprising similar to 30,000 observations of presences or absences of bee occurrences from structured surveys at 269 sites in northern Europe to investigate if flower preferences modulate species distributions across multiple environmental gradients. Bees were assigned a continuous functional trait separating preference for short vs. tubular flowers. Results: We observe that bee flower preference for either tubular flowers (Fabaceae) or plants with shallow flowers (including Apiaceae and Brassicaceae) can be described by a continuous flower preference trait score. The likelihood of observing a bee along a latitudinal gradient-encompassing variation in temperature, atmospheric N deposition and elevation-is dependent on its flower preference trait score. Specifically, bees with preferences for tubular flowers have a higher likelihood of occurrence with higher latitudes, while bees with preference for non-tubular flowers increase towards the south. Main Conclusions: Our results improve our understanding of how species-specific variation in flower preferences drives community-wide shifts in diversity and can therefore help devise region-specific conservation strategies.