Hotspots on cold mountains: Hot flowers as pollinator refuges in mountain ecosystems

Abstract Mountain environments constrain the activity of ectothermic insects. Yet, fine‐scale thermal refuges can buffer these thermal constraints, helping insects remain active in cold conditions. Previous work has demonstrated that some flowers experience substantial floral warming, with temperatures exceeding ambient air temperature. This raises the question: do flowers offer thermal benefits that influence insect activity at the plant–insect community scale? To test whether subalpine and alpine flowers function as warm microhabitats for insect pollinators, we quantified flower temperatures across a diverse plant community in the Australian alps and examined the relationship between flower temperature and the frequency of flower–insect interactions. We found that most plant species exhibited floral temperatures above ambient air temperatures, with the difference sometimes exceeding 10°C. Environmental conditions, especially UV irradiance index, were associated with enhanced warming, while increased relative humidity was associated with lower flower temperatures. Among the floral traits we examined, shape was the strongest predictor of warming, with globular, cup‐ and star‐shaped flowers warming most strongly, whereas tubular and bell‐shaped flowers only warmed slightly above air temperature. Insect body temperature was also typically warmer than floral tissues. Notably, we found that when ambient conditions were cool, warm flowers received significantly more insect visits, especially from Diptera. This effect weakened as ambient temperature increased. Our results indicate that some flowers may provide insects with a thermal reward when ambient conditions are otherwise activity limiting. Our results offer community level insights suggesting that naturally warmer flowers attract more insect visitors during cold conditions, thereby connecting ambient temperature, floral microhabitat and insect activity across a mountain plant–insect assemblage. Read the free Plain Language Summary for this article on the Journal blog.