Species-habitat networks inform pollinator conservation strategies in cities

As more people live in cities, research on the ecological role of urban green for pollinators is accumulating. However, most studies have focused on the diversity patterns at the local scale, while an urgent question is to understand how to manage whole cities to maximise pollinator conservation. Here, we selected 105 sites belonging to 6 habitat types (abandoned meadows, crop field margins, gardens, parks, parks managed with a pollinator friendly mowing regime, and road margins) in the city of Padua (Italy). We sampled bees and hoverflies using transect walks, from spring to late summer, and analysed species-habitat networks to understand how pollinator communities were organized across urban green areas. We found that most pollinator species interacted with most habitat types in the city, creating a highly generalistic and robust network. Compared to all other habitats, road margins had a very small influence over the network and hosted the lowest pollinator abundance and species richness. Green areas in the landscape positively affected wild bees but local patch quality, in terms of flowers and low mowing regime, was key. Network robustness decreased when the patches with the highest quality were removed first, and pollinators depended on the patches with the highest flower cover and vegetation height. Except for road margins, all habitat patches could support pollinator species. Therefore, urban planning strategies could be tailored without considering habitat identity, for example by increasing the overall amount of green areas and by implementing management practices that enhance the floral resources across all urban green spaces.