Bigger is not better: Larger bees face greater risks from climate change

Abstract

Body size plays a fundamental role in how animals respond to their environment. Smaller animals are more vulnerable to heat loss and desiccation due to their high surface-area-to-volume ratio. I investigated the relationship between bee body size and climate response by measuring physiological tolerance in the lab and physiological resistance in the field. I found that small bees are cooler while foraging than larger bees, but body size does not significantly affect thermal tolerance. I found that smaller bees are drier but have a greater desiccation tolerance, which evolved due to regular exposure to high desiccation risk. For all results except for desiccation tolerance, relationships are independent of phylogenetic relatedness. Finally, larger bees are closer to their absolute physiological limits and therefore may be at increased risk to the effects of climate change. If we see declines in large bees, we may see changes in pollination services and plant communities.