Biotic homogenization and functional restructuring of bee communities in northern France: implications for conservation priorities

Anthropic-related pollinator decline is a major challenge. To ensure that we characterize the underlying ecological processes and implement appropriate conservation measures, it is important to consider multiple dimensions of diversity. Here, we use a rare dataset of bee communities spanning over 100 years (1910–2019) in northern France, an area subject to severe land use alteration. By analyzing species-level data together with functional traits, we demonstrate a significant decline and homogenization of taxonomic diversity associated with a functional restructuring of bee communities. By combining extinction probabilities based on Red List categories with functional characteristics, we identified species critical for maintaining functional diversity and in need of urgent conservation actions. Present-day communities exhibited functional shifts favoring larger, eusocial generalist species with a long phenology, likely reflecting greater adaptability to reduced resource availability in space and time. Species with higher thermal resistance and warmer climatic niches were favored over time, indicating functional filtering of species adapted to climatic warming. In addition, recent bee communities were characterized by species with larger habitat breadth and stronger affinity for artificial habitats. These changes resulted in decreased functional evenness and increased dominance of species with extreme trait combinations, reducing functional redundancy and potentially destabilizing ecosystem processes. Suitable habitats and host plants are identified and recommended for supporting the most functionally threatened bee species. Our findings underscore the importance of considering functional traits in conservation prioritization efforts, and advocate a more integrated approach that incorporates both taxonomic and functional perspectives to effectively mitigate bee biodiversity loss.