Local Climatic Effects on Colonisation and Extinction Drive Changes in Mountain Butterfly Communities

ABSTRACT Aim The capacity of cool refugia to protect cold‐adapted species against climate change may depend on both their initial climatic conditions and how quickly these change. We test how local climatic conditions influence mountain butterfly communities via their effects on colonisation and local extinction. Location Four mountain ranges in Central Spain. Methods We used community temperature index (CTI), based on the climatic niches of constituent species (species temperature index, STI), to estimate thermal affinities for butterfly communities sampled in 1984–2005 to 2017–2022. We related CTI to local temperature, estimated using the model Microclima , and tested for changes to local temperature and CTI over time. We used standard deviation in CTI (CTI SD ) and species richness to detect effects of colonisation and local extinction on community change. Finally, we tested for differences in thermal affinity and thermal niche breadth (STI SD ) between species undergoing local extinction or colonisation at each site. Results CTI was positively related to local temperature in both periods. However, there were regional differences in rates of change in CTI and local temperature. CTI increased overall, even though temperatures decreased at many sites; and CTI increases were greatest in historically cool sites. Neither CTI SD nor species richness changed overall, suggesting that communities experienced equivalent numbers of colonisations and extinctions. Colonising species had warmer thermal affinities than those undergoing local extinction, and species with broader thermal niches increased their occupancy most over time. Main Conclusions Local climatic conditions influenced changes to community composition based on species thermal tolerances, resulting in the loss of communities where cool‐affinity species predominated, and a narrower range of community thermal affinities overall. Our results suggest that a regional perspective to identifying climate change refugia is needed to provide a wide range of local climate conditions and rates of change to help adapt conservation to climate change.