Morphological traits are linked to the cold performance and distribution of bees along elevational gradients

Abstract Aim Identifying traits that enhance the success of animals in unhospitable climates helps to understand biogeographical patterns and to predict the consequences of climatic changes. On temperate mountains, traits that increase cold performance potentially allow species to colonize higher elevations. We first tested the importance of morphological traits for the cold performance of bees. Second, we assessed the relevance of these traits for species distributional patterns by analysing intraspecific and interspecific trait shifts along elevational gradients. Location National Park Berchtesgaden, Germany; Würzburg, Germany. Methods We determined thermal activity thresholds by measuring signs of immobility along temperature gradients under laboratory conditions and related them to morphometric traits. We sampled bee communities at 34 sites along an elevation gradient in the northern Alps, measured for all species morphometric traits and thermal activity limits in the field, and analysed how trait measures changed with elevation within and across species. Results Laboratory and field experiments revealed that bees with larger body size, longer hair and relatively short wings tolerated lower temperatures before reaching immobility and started being active in the field at lower temperatures than small, short‐haired and long‐winged species. In correspondence to these results, we found that morphometric traits increased (body size, hair length) or decreased (relative wing length) with increasing elevation in communities and, in case of body size, also within species. Main conclusions Results of laboratory and field experiments and their reflectance in community‐ and species‐level trends of morphological traits along elevational gradients underscore the adaptive nature of large body size, long hair and short wings for bees’ thermal performance. Morphological traits expanding lower thermal limits probably contribute to the fitness of bees in cold environments and may simultaneously be under selection in a warming world.