DISENTANGLING THE EFFECTS OF HUMAN-ALTERED ENVIRONMENTS ON POLLINATORS AND THEIR INTERACTION WITH PLANTS: AN INTEGRATIVE ASSESSMENT.

Pollination is mainly mediated by animals and is fundamental for plants reproduction and for maintaining ecosystem resilience and human wellbeing. However, pollinator decline is occurring at the global scale due to multiple threats, related to human activities, with the intensification of land use ranking first. This phenomenon, driven by the growing urbanization and agricultural pressures, directly or indirectly affect pollinator communities, causing biodiversity loss, altering plant-pollinator interactions, and thus impairing the overall pollination service. In this PhD thesis the effects of land use composition and configuration have been investigated at different levels (e.g., species, community, and interactions). A multidisciplinary approach has been adopted, through the integration of field sampling activities and GIS-based analyses, with laboratory ones, such as morphometric evaluations, analysis of pollen deposited on flower’s stigmas and taxonomic identification of pollen and insects through DNA-based tools (e.g., DNA metabarcoding). The general aim of this PhD project was to provide advice for land use management policies has been addressed through intermediate goals, treated in different case studies. In the first study case, the effects of urbanization and agricultural land uses have been addressed by focusing on pollinator insects and plants inhabiting smallholder farms of Tanzania. The obtained plant-pollinator networks indicated a general decrease of pollinator richness with increasing proportion of urban and agricultural land, and an increased competition for resources among individuals. At local scale, the availability of floral resources reversed this trend, thus supporting the adoption of nature-based solutions to create suitable conditions for pollinators. In the second study case, the effects green habitat fragmentation have been investigated in Maldivian islands. Results indicated that low degrees of green areas fragmentation in anthropic habitats promote pollinator richness but reduce the complexity of plant-insect interactions, reflecting a lower pollinators functional redundancy. The pollination efficiency seemed to be indirectly altered by fragmentation, thus, supporting the necessity of conservation efforts to promote and maintain a high pollinator biodiversity. In the third study case, we investigated the pollinator communities along a gradient of urbanization in the metropolitan area of Milan, confirming that low proportion of impervious surface and/or low fragmentation of green areas, may increase pollinators abundance. Pollinators have also been found to collect floral resources from less species in the more urbanized areas, confirming the simplification of plant-pollinator interactions. Flower resources also shaped their nutritional content in response to land use composition, with increasing sugar content in the more urbanized areas. The fourth study case, focused on pollinator morphological response to land use alteration. The higher temperatures resulting from increased proportion of impervious surfaces, shaped the morphological functional traits (i.e., body size and wing asymmetry) in two bumblebee species. Both species were negatively influenced by higher temperatures but showed idiosyncratic responses, with Bombus pascuorum reducing its body size and B.terrestris increasing wing asymmetry but not the body size. These results indicate that the microclimate conditions of urban landscapes influence insects development, likely reducing their dispersal ability. Overall, the results of this PhD thesis provide new insights for the design and management of anthropic landscapes, supporting the connection and maintenance of green spaces and nature-based solutions to reduce the impact on pollinators diversity and interaction with plants. Policy makers should consider these research outcomes in the future and integrate them into management actions, as also claimed by the “One health “concept.