Landscape characteristics predict body sizes in wild bees: implications for pollination services and foraging range

Declines in wild bee abundance and diversity may have cascading effects throughout ecosystems as well as negatively impact food security. Understanding the scale at which wild bees forage within agricultural landscapes is an important component of developing effective pollinator conservation strategies. Foraging ranges of wild bee species can provide insight into the extent to which wild bees pollinate crops. In the southern Great Plains, Brassica napus (canola) is an important edible oil, oilseed meal, and biofuels crop that benefits from bee pollination. We measured body size of three common wild bee species at increasing distances into canola fields (75, 150, and 300 m), as well as landscape characteristics and seed set of canola. We found positive intraspecific correlations between body size and distance into canola fields for two of the species, as well as seed set and distance into canola fields. We also found correlations between land use and body size across three nested spatial scales (250 m, 500 m, and 1 km). As the area of grass and pasture increased so did the body size of Agapostemon texanus (Cresson), whereas the body size of Lasioglossum disparile (Cresson) decreased. As the area of development increased, the body size of Colletes mandibularis (Smith) decreased. Body size variation at the population level may have implications for pollination efficacy and foraging ranges of wild bees and should be considered in future studies, particularly with a more robust sample size. Furthermore, intraspecific variation in body size may provide insights into species level responses to land use change and other environmental stressors.