Warmer environments harbor greater thermal trait diversity in moth assemblages.

Thermal trait diversity is critical for understanding species' responses to climate change, yet its ecological drivers remain unclear. Using eco-evolutionary simulations and empirical data from 653 moth species across three Asian elevational gradients, we examine how temperature regimes shape thermal strategies in assemblages. Warmer environments support larger hypervolumes of moth assemblages, reflecting a broader array of coexisting thermal strategies. Contrary to the climatic variability hypothesis, which predicts generalized traits under stable climates, we find that warmer sites foster assemblage-level diversity even while individual species retain narrow thermal tolerance ranges. Short-term temperature fluctuations exert minimal influence, while seasonal variability promotes generalists but reduces overall hypervolume. These results demonstrate that mean temperature, not variability, is the dominant force structuring thermal trait diversity. By revealing how thermal strategies assemble under different climates, our study provides a mechanistic basis for predicting biodiversity responses to warming and emphasizes the conservation value of low-elevation ecosystems.