Abstract
Predicting how species will respond to climate change and land use modification is essential for conserving organisms and maintaining ecosystem services. Thermal tolerances have been shown to have strong predictive power, but the potential importance of desiccation tolerances have been less explored in some species. Here, we report measurements of thermal and desiccation tolerances and safety margins across a gradient of urbanization, for three bee species: silky striped sweat bees (Agapostemon sericeus), western honeybees (Apis mellifera), and common eastern bumblebees (Bombus impatiens). We found significant differences in thermal tolerances, measured as critical thermal maximum (CTmax), amongst species. Bumblebees were the least sensitive to warming, with a higher CTmax (53.1 °C) than sweat bees (50.3 °C) and honeybees (49.1 °C). We also found significant differences in desiccation tolerances, measured as critical water content (CWC), between all species. Sweat bees were the least sensitive to desiccation, with the lowest CWC (51.7%), followed by bumblebees (63.7%) and honeybees (74.2%). Moreover, bumblebees and sweat bees were closer to their CTmax in more urbanized locations, while honeybees were closer to their CWC. These results suggest that bees have differential sensitivities to environmental change and managing for diverse bee communities in the face of global change may require mitigating both changes in temperature and water.
Highlights
Climate change and land use modification can have negative consequences for many species, leading to local population declines[1,2,3] and extinctions[4]
None have calculated a hygric safety margin, which we have used in this study and define here as the difference between critical water content (CWC) and field body water content
A post-hoc test revealed that bumblebees had significantly higher critical thermal maximum (CTmax) than honeybees and sweat bees, but there was no difference between honeybees and sweat bees
Summary
Climate change and land use modification can have negative consequences for many species, leading to local population declines[1,2,3] and extinctions[4]. The observed variations in desiccation tolerance may be due to local adaptations, or plasticity[37] These studies suggest that desiccation tolerance might be an important predictor of the effects of land use and climate change on animals. None have calculated a hygric safety margin (hygric = relating to moisture), which we have used in this study and define here as the difference between CWC and field body water content This metric could be highly informative in predicting potential responses to climate change, complementing thermal analogs. Urban areas can experience altered soil moisture[46], and soil moisture is found to vary among habitat types within and among cities[47] These changes in temperature and moisture availability can impact the field body water content of arthropods[48]. Others have found that changes in insect water balance can have consequences on growth, reproduction, and survival[51]
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