Urbanisation impacts the diversity, coloration, and body size of wild bees in a Mediterranean city

Abstract

Urbanisation is a growing phenomenon causing the decline of wild bees globally. Yet, bees manage to persist in the urban matrix thanks to islands of vegetation in public parks and private gardens. While we begin to comprehend the impact of urbanisation on bees diversity and abundance, our understanding of its impact on the functional diversity of wild bees is limited. Here, we use an integrative approach to investigate the response of wild bees to urbanisation at the community, species, and individual levels. To do so, we sampled wild bees in 24 public parks along an urbanisation gradient in the Mediterranean city of Marseille. We found that species richness and abundance decreased in more urbanised areas, but increased in larger city parks. Moreover, larger individuals within species, but not larger species, were found in larger city parks, suggesting that park size is crucial for the persistence of bees in cities. Interestingly, we show that brighter species were found in parks surrounded by a large amount of impervious surface, highlighting the importance of colour traits in the response to environmental changes. Finally, our results revealed that larger species, but not larger individuals, were also more colourful. In summary, our study not only confirmed that urbanisation negatively impacts community-level traits, but that it also affects species coloration and individuals body size, thus improving our understanding of the functional response of wild bees to urbanisation. We suggest that increasing park size may compensate for the negative effects of urbanisation on wild bees.