Defensa de la Tesis Doctoral de Guim Ursul titulada "European mountain butterfly distributions and diversity as a model to understand the conservation implications of climate change"

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Thesis summary: 

Climate change is a major threat to biodiversity, driving local extinctions, colonisations and community turnover, as species shift their ranges along latitude and elevation gradients. Mountain ecosystems, characterized by steep thermal gradients and microclimatic heterogeneity, offer ideal conditions for studying these dynamics. This thesis analyses how European mountains, with an emphasis on the Iberian Peninsula, can serve as climate refugia for butterflies in the face of climate change. First, a literature review was conducted to explore how climate refugia contribute to maintaining insect diversity and thus demonstrate how these refugia have historically shaped species distributions and the importance they may have in the face of current climate change.

Historical butterfly data from Central Spain were used to compare community composition between 1985–2005 and 2017–2022, revealing shifts in altitudinal ranges and species composition linked to local climate. The results showed a general “thermophilization” of communities driven by colonisations of warm-affinity species and local extinctions of cold-affinity species. Thermal specialist species declined, while generalists became more dominant. However, regional differences emerged, demonstrating the influence of local climates on changes in community composition. Regarding species' elevational changes, many species shifted their altitudinal ranges upward, especially at their lower range limits, resulting in overall range contractions. This trend underscores the increasing loss of species in lowland areas and suggests that species may already be reaching their upper elevation limits. These shifts were most pronounced in species with cold affinities (greater climate sensitivity) and those occupying lower elevations (greater climate exposure), underscoring their vulnerability to climate change. These results demonstrate the usefulness of incorporating sensitivity and exposure indicators into climate vulnerability assessments for species. 

This thesis also examined how local climate influences the thermal affinities of butterfly communities (Community Temperature Index, CTI) across three European mountain regions: Central Spain, Catalonia/Andorra and South Tyrol in Italy. Results showed consistent CTI-temperature relationships across regions indicating the importance of climate as a driver of biogeographical variation in butterfly communities. Regional differences in species pools — such as the dominance of warm-affinity species in Central Spain and cold-affinity species in South Tyrol — reflected broad-scale climatic gradients shaped by species’ thermal affinities. However, when considering only species shared among regions, CTI responded consistently to local temperature, indicating that local adaptation had little effect on this indicator. These findings support the use of CTI as a reliable tool to assess community-level responses to climate change across regions. 

In summary, this thesis highlights temperature as a key driver of climate change responses along altitudinal gradients, with cold-affinity and thermal specialist species being the most threatened. Resampling historically studied sites along these gradients proved effective in identifying patterns in community composition changes and altitudinal range shifts. The results provide new evidence on the importance of climate refugia for species conservation in mountainous areas under recent climate change.