Landscape heterogeneity correlates with bee and pollen diversity while size and specialization degree explain species-specific responses of wild bees to the environment.

Access to adequate pollen sources in agricultural landscapes is critical for the nutrition and development of bees. The type and quantity of pollen available to bees and may be determined by local plant diversity, land-use intensity and landscape structure but different bee species likely respond differently to these parameters. Identifying community and specific responses is therefore imperative to understand pollinator population dynamics in agricultural landscapes. We sampled bees in 36 plots along a land-use gradient at 4 sites in Belgium and Germany over two years. We collected 1821 bees from 100 bee species and constructed a pollen foraging network with 36 common wild bee species based on pollen metabarcoding. We investigated differences in community responses and species-specific responses to environmental variables. Landscape heterogeneity positively correlated with bee species richness, diversity and functional richness, and significantly explained bee community composition per plot. Bee collected pollen diversity correlated with bee species diversity. Furthermore, landscape heterogeneity positively correlated with bee collected pollen diversity when pooling abundant bee species, while it did not correlate with pollen diversity of the most abundant generalists. Land-use intensity and local plant diversity had no significant effect on bee diversity. Larger bees showed negative responses to increasing land-use intensity and bees with more specialized diets showed positive correlations with landscape heterogeneity. Our study goes beyond mere floral diversity and provides new insight into the responses of wild bee communities to landscape structure and regional pollen availability, as well as the interplay between bee abundance and pollen foraging traits. Our results highlight the importance of determining species-specific nutritional needs and considering landscape level structure in pollinator conservation programs.

Critical links between biodiversity and health in wild bee conservation.

Wild bee populations are declining due to human activities, such as land use change, which strongly affect the composition and diversity of available plants and food sources. The chemical composition of food (i.e., nutrition) in turn determines the health, resilience, and fitness of bees. For pollinators, however, the term 'health' is recent and is subject to debate, as is the interaction between nutrition and wild bee health. We define bee health as a multidimensional concept in a novel integrative framework linking bee biological traits (physiology, stoichiometry, and disease) and environmental factors (floral diversity and nutritional landscapes). Linking information on tolerated nutritional niches and health in different bee species will allow us to better predict their distribution and responses to environmental change, and thus support wild pollinator conservation.