Opposing pressures of climate and land-use change on a native bee

Anthropogenic activities are rapidly changing the environment, and species that do not respond face a higher risk of extinction. Species may respond to environmental changes by modifying their behaviors, shifting their distributions, or changing their morphology. Recent morphological responses are often measured by changes in body size. Changes in body size are often attributed to climate change, but may instead be due to differences in available resources associated with changes in local land-use. The effects of temperature and land-use can be uncoupled in populations of the small carpenter bee Ceratina calcarata, which have experienced changes in agricultural and urban cover independent of climate change. We studied how the morphology of this bee has changed over the past 118 years (1902-2019) in relation to climate change and the past 45 years (1974-2019) in relation to agricultural and urban cover. Over this time, summer temperatures increased. We found that male and female size decreased with increasing temperature. Male size also decreased with agricultural expansion. Female size, however, increased with agricultural expansion. These results suggest that rising temperatures correlate with a decrease in female body size, while, opposite to predicted, agricultural land-use may select for increased female body size. These opposing pressures act concurrently and may result in bee extirpation from agricultural habitats if selection for large sizes is unsustainable as temperatures continue to increase. Furthermore, this study emphasizes the need to consider multiple environmental stressors when examining the effects of climate change due to their interactions.

Automated summary

Anthropogenic activities are rapidly altering the environment, leading to potential changes in the morphology, distribution, and behaviors of species, thus increasing the risk of extinction. Changes in body size in populations of the small carpenter bee Ceratina calcarata are influenced by both climate change and agricultural expansion, with increasing summer temperatures leading to decreased male and female size, while agricultural expansion may result in increased female size. These opposing pressures highlight the complexity of environmental stressors interacting with each other.