The influence of nutrients in pollen and nectar on the foraging patterns of wild bees and plant-pollinator network structure is a critical but understudied component of pollination ecology. We address this issue by quantifying the composition of pollen protein and nectar carbohydrate content and observing plant-pollinator interactions in an intact subalpine community to explore the influence of floral nutrients on plant-pollinator interaction network structure. To do so, we observed bee-flower interactions across six sites, quantified the protein content of pollen and carbohydrate content of nectar in 10 different bee-visited plant species, and performed quantitative analysis of visitation and nutrient network structure. We ask the following questions: (1) What is the protein and carbohydrate composition of the subalpine wildflower meadows? (2) Do foraging bees prefer plants with higher pollen protein and nectar carbohydrate content? And (3) How does nutrient content contribute to plant-pollinator interaction network structure? We hypothesized that there would be variation among plant species in nutrient content (protein and carbohydrates), that bee species will differ in their preferred protein and carbohydrate sources, and that the structure of the protein networks will exhibit greater specialization, lower nestedness, and lower connectance compared to visitation and carbohydrate network structure.
Results/Conclusions
Overall, protein and nectar content varied considerably among plant species, and also varied across the growing season. Bees tended to prefer pollen with greater protein content, whereas we did not find evidence that bees exhibited strong preferences for nectar carbohydrate content. Bee species tended to be more generalized in their pollen resource use during spring (early-season) and late summer, whereas bees were more specialized in their pollen collection during mid-season (summer). The structure of pollen protein-acquisition networks showed greater specialization compared to visitation and the nectar carbohydrate networks. Additionally, protein networks contained fewer links per species and lower nestedness compared to the visitation networks. Carbohydrate networks had higher links per species and nestedness, but lower specialization (H2’) than the protein and visitation networks. These preliminary findings indicate that wild bees exhibit nutritional preferences that influence their foraging decisions and ultimately the structure of interaction networks. These results contribute to our understanding of the nutritional ecology and foraging ecology of wild bees, and how floral nutrients influence plant-pollinator interaction network structure.