Background/Question/Methods Food is essential for the survival, health, and reproduction of organisms and shapes species interactions. However, the influence of macronutrient availability on species interactions in natural environments remains unclear. As a result, we lack a basic understanding of whether species occupy distinct or similar nutrient niches in natural environments. We address this using an 8-yr dataset of plant-pollinator interactions (bumble bees and flowering plants) coupled with extensive field surveys of macronutrients in pollen to ask: (1) How variable is the pollen macronutrient landscape across species, space, and time? (2) To what extent do pollinators occupy distinct macronutrient niches? (3) Which traits (tongue length or emergence phenology) underlie pollinator macronutrient niches?
Results/Conclusions We show that the macronutrient profiles of plant species are variable and dynamic throughout the growing season. Bumble bees in this community occupy two distinct macronutrient niches: one with higher protein, lower lipid, and lower carbohydrates, and another with lower protein, higher lipid, and higher carbohydrates. Species occupying each niche are best predicted by tongue length, with longer-tongued species in the higher protein niche and shorter-tongued bees in the lower protein niche. Within species, nutrient niches shifted between queens and workers for shorter-tongued species but were consistent across colony life stages for longer-tongued species. These results contribute to our understanding of how nutrients influence plant-pollinator interactions and how co-occurring animal species partition food resources in natural environments.
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