Grueter, C.; Segers, F. H. I. D.; Hayes, L.

Bees require a diverse diet for a healthy development. Many bee species show flower constancy, that is, they visit flowers of just one species during a foraging trip. Flower constancy is important for plant reproduction, but it could impair dietary diversity in bees, especially in biodiversity-depleted, human-modified landscapes. It is assumed that flower constancy does not lower dietary diversity in social bees, such as honey bees or bumble bees, because different colony members can specialise on different plant species. However, this has never been tested. We used computer simulations to investigate the effects of flower constancy on colony diet in plant species-rich and species-poor landscapes. We also explored if communication about food sources, which is used in many social bees, further reduces forage diversity. Our simulations reveal an extensive loss of forage diversity due to flower constancy in both plant species-rich and species-poor environments. Small colonies often discovered only 30-50% of all available plant species, thereby increasing the risk of nutritional deficiencies. Our simulation results could explain why bumble bees, which have small colony sizes, are less flower constant than honey bees and stingless bees, which have larger colony sizes. Remarkably, when colonies also communicated about food sources, Simpson\'s diversity, which measures the evenness of flower visits, approached near zero in plant species-poor environments. Finally, we found that food source clustering, but not habitat fragmentation impaired dietary diversity. These findings can help in the design of landscapes that increase forage diversity and improve bee nutrition and health in human-modified landscapes.