Behaviour 2019
Intraspecific variation and behavior in bumble bees: population-level consequences
Matthew W. Austin, Aimee S. Dunlap. University of Missouri - St. Louis, St. Louis, MO, United States

Bumble bees are experiencing divergent population trends; while some species are declining, others are thriving. Rapid environmental change is a likely driver of declines, but less is known about traits that make certain species more susceptible to decline. Two traits may be particularly consequential: intraspecific body size variation and behavioral plasticity. In bumble bees, body size variation is likely adaptive at the colony level and behavioral plasticity may enable matching behavior to environmental conditions. Across 31 bumble bee species, we find species with greater body size variation were more likely to have increased relative abundance over time. We did not find support for a link between behavioral plasticity (via a brain size proxy) and population trend. However, direct tests of cognition in the field suggest species that have undergone decline exhibit a temporal trend in behavioral plasticity - i.e. less plasticity early in the season, more plasticity late in the season - while thriving species do not. Our results suggest intraspecific trait variation and behavior are consequential for populations in changing environments and affect bumble bee population dynamics.