Future Climate Change and Bioclimatic Suitability of Two Endemic Balkan Water Frogs

Aim: To evaluate the impacts of future climate change on the bioclimatic suitability of two endemic water frogs of the southwestern Balkans, focusing on species- and lineage-level responses and implications for conservation. Location: Southwestern Balkans, including Albania, Greece and Montenegro. Methods: We applied an ensemble bioclimatic suitability modelling framework based on multiple algorithms, using selected bioclimatic predictors to estimate current suitability and to project future distributions under two Shared Socioeconomic Pathways (SSP2-4.5 and SSP5-8.5) for 2050 and 2070. Intraspecific patterns were assessed by integrating mitochondrial lineage data to evaluate stability for both species and lineage levels. Results: Both species are predicted to experience an overall decline in bioclimatic suitability under future climate scenarios, indicating broadly similar responses to climate change. However, the magnitude of these changes differs substantially. Pelophylax shqipericus is predicted to undergo more pronounced range contraction and fragmentation, whereas P. epeiroticus shows relatively higher spatial persistence, with suitable areas remaining primarily in lowland coastal regions. Lineage-level analyses reveal uneven patterns of vulnerability, with greater losses generally affecting phylogenetic lineages occupying more restricted or environmentally sensitive parts of the range. Main Conclusions: Regardless of the differences in their realized bioclimatic niches, both species respond in a similar direction to projected climate change. This suggests that shared climatic constraints outweigh niche differentiation in shaping future distributions. However, differences in the magnitude of response highlight species-specific and lineage-specific sensitivity to environmental change. These findings emphasize the importance of incorporating intraspecific diversity into climate vulnerability assessments and conservation planning in biodiversity hotspots.