Body size influences how animals exchange heat and water with their environment, shaping their ability to cope with climatic extremes. While often used interchangeably, "resistance" refers to an organism’s ability to buffer internal conditions from environmental change (e.g., avoiding overheating), whereas "tolerance" refers to its ability to survive once critical limits are reached (e.g., enduring extreme heat or water loss). To investigate how these traits scale with body size, we measured thermal and hygric resistance and tolerance in over 2,500 field-caught bees representing more than 30 genera. Contrary to common assumptions, our results showed that large bees—not small bees—face the greatest risks from heat and drought. These findings highlight how body size shapes physiological vulnerability and underscore the value of incorporating size-based traits into models predicting pollinator responses to climate change.
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