COS 135-5 - The influence of pollen macronutrients on plant-pollinator interactions

Background/Question/Methods

Pollination is an essential mutualistic interaction that facilitates plant reproduction while providing pollinators with food resources. Understanding how nutrients contained in pollen and nectar influence plant-pollinator interactions is a critical but understudied component of pollination ecology. We know very little about the quantity and quality of floral nutrients available to pollinators in natural ecosystems, nor how pollinators respond to the availability of these different floral nutrients. We ask the following questions: (1) How do plant species vary in their macronutrient composition? (2) How does macronutrient acquisition vary among wild bumble bee species, and how does it compare to what is available? And (3) How does network structure vary among nutrient and visitation networks? To answer these questions, we observed plant-pollinator interactions across the entire growing season for two consecutive years; we quantified pollen macronutrient composition (protein, lipid, and carbohydrates) for 34 species in a subalpine plant community; and we quantified the macronutrient composition of wild bumble bee pollen loads.

Results/Conclusions

Overall, macronutrient composition varied considerably among plant species. The early season plant species exhibited high protein to lipid ratios, compared to late-season species, which exhibited low protein to lipid ratios. Pollen load macronutrient composition varied among wild bumble bee species, indicating that bees differ in their nutritional preferences or ability to acquire nutrients from the resource landscape. All nutrient networks exhibited lower levels of interaction complexity than visitation networks (as indicated by lower linkage density). Pollen protein network structure showed greater specialization than the lipid and carb networks. Protein networks displayed greater niche overlap for pollinators than lipid and carbohydrate networks, suggesting that there is more competition for protein resources and that protein may be a limiting resource in this community. These results contribute to our understanding of the nutritional ecology of wild bees and how floral macronutrients contribute to emergent network structure.