COS 19-3 - Macronutrient acquisition niches of a wild bumble bee community

Monday, August 7, 2023

2:00 PM – 2:15 PM PDT

Location: E143

Presenting Author(s)

JB

Justin A. Bain

PhD Candidate
Northwestern University, Chicago Botanic Garden, & Rocky Mountain Biological Laboratory, United States

Coauthor(s)

JO

Jane E. Ogilvie

Rocky Mountain Biological Laboratory, Australia
PC

Paul J. CaraDonna

Northwestern University, United States

Abstract: Background/Question/Methods

Nutrients are essential for organismal survival, health, and reproduction and regulate population dynamics. Yet, we still know little about how nutrients influence species interactions in natural environments. Because nutritional information is so limited, a simplifying assumption is made that food resources are nutritionally equivalent and diverge only in energy content and, therefore, species foraging for similar food resources should occupy similar nutrient niches. As a result, we lack a basic understanding of whether species occupy distinct or similar nutrient niches and how nutrient niches influence species interactions. We address this knowledge gap using an 8-yr dataset of plant-pollinator interactions (bumble bees and flowering plants) coupled with extensive field surveys of macronutrients (protein, lipid, carbohydrate) in pollen to ask: (1) To what extent do wild pollinators occupy distinct macronutrient niches? (2) Which traits—tongue length, body size, phenology— underlie pollinator macronutrient niches? (3) How does pollinator macronutrient acquisition influence interaction network properties?

Results/Conclusions

We show that wild pollinators (bumble bees) in the focal community occupy two distinct macronutrient niches: one group of species occupying a high protein-to-lipid ratio niche space and the other occupying a more evenly balanced macronutrient ratio niche space. The species occupying each nutritional niche space are best predicted by differences in tongue length. Our examination of interaction network properties demonstrates that protein acquisition networks were less modular, and interactions were less evenly distributed compared to lipid, carbohydrate, and visitation networks. Furthermore, species occupying the more evenly balanced macronutrient niche were more specialized for protein than other macronutrients. In contrast, the high protein niche species were more generalized (less specialized) for protein than the other macronutrients, suggesting that wild bumble bee species have varying macronutrient priorities. These results contribute to our broader understanding of species’ dietary niches as well as how coexisting pollinator species partition resources in natural environments.