Intraspecific variation in worker body size makes North American bumble bees (Bombus spp.) less susceptible to decline

Population declines have been documented in approximately one-third of bumble bee species. Certain drivers of these declines are known, however less is known about the interspecific trait differences that make certain species more susceptible to decline. Two traits, which have implications for responding to rapidly changed environments, may be particularly consequential for bumble bee populations: intraspecific body size variation and brain size. Bumble bee body size is highly variable and is likely adaptive at the colony level, and brain size correlates with cognitive traits (e.g. behavioral plasticity) in many groups. Trait variation and plasticity may buffer species against negative effects of rapidly changed environments. Using phylogenetically controlled analyses of 31 North American bumble bee species, we find higher intraspecific body size variation is associated with species having increased their relative abundance over time. However, this variation does not significantly inter...