ENVIRONMENTAL FACTORS INFLUENCING POLLEN COLLECTION AND DEVELOPMENT IN HONEY BEE COLONIES AND ANALYSIS OF POLLINATION NETWORKS IN ECOSYSTEMS IN NORTHWESTERN SARDINIA

This thesis investigates how environmental factors, such as habitat diversity and type, influence pollen availability, diversity, and plant-pollinator network structures. Following a general introduction on the importance of pollination and the causes behind pollinator decline (Chapter 1), Chapter 2 examines how landscape features affect pollen availability and honey bee colony performance in a Mediterranean agro-sylvo-pastoral region (Sardinia, Italy). Pollen was collected over one year from colonies in four sites along a landscape heterogeneity gradient. Colony development was assessed periodically. Results showed a positive correlation between pollen quantity and semi-natural habitat cover, while landscape diversity enhanced pollen richness and diversity. Colony growth was strongly linked to pollen richness, diversity, and quantity, emphasizing the critical role of diverse diets supported by semi-natural habitats. Chapter 3 provides the first comprehensive survey of wild bees and plant-bee interactions in Sardinia. Four sites were studied: two in natural habitats (Asinara) and two in agroecosystems (Nurra). A total of 1,491 wild bees from 123 species were collected, with higher species richness and diversity in Nurra. Plant-bee networks showed high complementarity, modularity, and low connectivity, indicating vulnerability. Differences in network structure across sites were influenced by habitat heterogeneity. Chapter 4 evaluates two bee sampling methods—colored pan traps and transect walks—on Asinara island. Transects recorded greater species richness and diversity but fewer individuals, while pan traps were more effective during low floral abundance. Eighteen species were captured exclusively by pan traps, particularly from July to October, highlighting the value of alternating methods seasonally for a comprehensive and efficient survey of bee communities.