Authors: Geppert, Costanza; Cappellari, Andree ;Corcos, Daria;Caruso, Valerio;Cerretti, Pierfilippo ;Mei, Maurizio ;Marini, Lorenzo;

Urbanization is widely regarded as a major threat to biodiversity. However, recent research highlighted the ecological importance of cities for pollinators. Key determinants of cities’ ability to sustain pollinators are the amount and the spatial organisation of green areas. In addition, temperature is expected to be of primary importance for pollinator activities. Here, we aimed at disentangling the effects of temperature, open habitat cover and distance from the city centre on wild bee communities in the city of Rome (Italy). We selected 36 sites along two independent gradients of surface temperatures and of open habitat, and we sampled bee communities using pan traps for four months. Then, we measured functional traits of wild bees, i.e., body size, social behaviour, nesting strategy, and diet breadth. Temperature emerged as the main driver of wild bee communities. At warmer temperatures, communities were richer in species and individuals. In addition, with increasing temperatures, bee communities showed a higher percentage of polylectic and small size species. Here, we showed that in a highly urbanised environment, temperature shapes pollinator communities irrespective of other landscape metrics. Warming seemed beneficial for bee abundance, but it might homogenise communities selecting for those traits that make species more easily adaptable.