Pollinators of Rome: taxonomic, functional diversity and pollination networks as a tool for greening and forestry actions for a big city

The considerable number of large urban green areas within Rome is a rare case in Europe, in fact, the Rome municipality has the largest area occupied by green spaces on the continent. As urbanisation progresses globally, we realise how important these green areas can be as bulwarks for protecting and conserving animal and plant diversity within the urban ecosystem, mitigating the effects of habitat fragmentation and loss. This is why Rome's nature reserves represent an excellent model for studying the impact of large urban green spaces on the diversity and abundance of bee communities being immersed in a matrix deeply modified by infrastructures and human activities. Bees, particularly wild bees, represent one of the most efficient and important groups of insect pollinators, responsible for contributing substantially to the ecosystem service of pollination of most wild, cultivated, exotic and ornamental flowering plants. The diversity of botanical and bee species in an area is directly related. Underlying this link between plants and pollinating insects, which has evolved since the Cretaceous period, is the specialisation of different groups of bees in visiting specific flower types to satisfy their metabolic needs. At the same time, flower plants have evolved morphologically and physiologically to attract insects that favour their reproduction by conveying the pollen produced by an individual to its conspecific. Furthermore, the pollination service bees provide plays a crucial role in maintaining the functionality of ecosystems, including the urban ones. The disturbance produced by urbanisation is the product of multiple biotic and abiotic factors that occur with varying intensity along the urban-rural gradient. This means that the pressure exerted on biological communities by urban disturbance manifests itself with different intensities in different areas of the city, which are directly related, by convention, to the distance of a site from the city centre, representing the more intensely urbanised area. In this study, it emerges that Rome hosts a remarkable wealth of wild bee species in its nature reserves, including threatened species. In addition, interactions with spontaneous herbaceous plants found in the areas are analysed to provide useful indications for urban green areas management to increase the diversity of wild bees. Furthermore, it emerges that the groups constituting the bee communities respond variably, in space and time, along a true urban-rural gradient that can be observed within the Appia Antica regional park, which is the largest urban green area in Europe.