Hauling field gear up Gothic Mountain…
Climate change is rapidly altering mountain ecosystems by increasing temperatures, reducing snowpack, and extending growing seasons. These changes can result in shifts in species distributions and ecological interactions. While elevational range shifts have been well documented in bumble bees, comparatively little is known about how solitary bees respond to changing climatic conditions. This study investigated whether the ultra-green sweat bee, Agapostemon subtilior, has expanded its elevational range in Gunnison County, CO, in response to climate change. Occurrence records of A. subtilior collected from 2010-2023 across sites spanning an elevational gradient from approximately 2400 meters to 3400 meters were compiled using data from the Rocky Mountain Biological Laboratory (RMBL) Irwin long-term bee phenology monitoring program. Records of A. subtilior were integrated with environmental variables including elevation, temperature, and precipitation obtained from the RMBL Data Hub. Negative binomial generalized linear models were used to test the effects of those environmental variables on A. subtilior abundance. Elevation was found to be a strong and significant predictor of abundance, with significantly higher abundance at low-elevation sites. Temperature and precipitation were both significantly associated with abundance, but they also both closely tracked the elevational gradient. However, no significant trend in abundance was detected across sampling years. These results suggest that climate variables are closely tied to current patterns of A. subtilior abundance across elevation. This study highlights the need for longer-term monitoring to assess whether solitary bee distributions are beginning to to move with climate change in mountain ecosystems.
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