Modeling habitat suitability and connectivity for the sole endemic genus of Italian vertebrate: present and future perspectives

Background: Amphibians are the most globally threatened vertebrates, facing a particularly high risk of extinction in some regions, such as the Mediterranean basin. Within this region, the genus Salamandrina, comprising two species of notable conservation concerns, managed to persist throughout historical climate changes exclusively along the Italian peninsula. Among the main threats to this genus are habitat loss and climate change, as this salamander is adapted to humid forests and relies heavily on water sources, such as small streams, for reproduction. In this study, we employed fine-scale species distribution models (SDMs) to estimate areas projected to remain suitable for Salamandrina species in the future and areas expected to become unsuitable, incorporating bioclimatic, topographic, and habitat variables. We also evaluated landscape connectivity and identified ecological corridors that could facilitate movement through circuit-theory techniques, analyzing potential changes under different scenarios. Additionally, considering known hybridization events in a contact zone between the two species, we measured connectivity to assess whether this process might change in the future. Results: We found several suitable areas that mostly align with the known ranges of both species. Future projections showed an overall decline in habitat suitability, with a northwestern shift. While strong in certain areas, landscape connectivity is expected to decrease overall. Specifically, our results revealed several corridors for S. perspicillata (the northern species), with higher connectivity values in the Central Apennines. For S. terdigitata (the southern species), a crucial corridor in the Catena Costiera Massifs, in the western southernmost region of the Italian peninsula, connects two key conservation areas. In the contact zone, we identified corridors that could favor hybridization between the species, with predictions suggesting an increase. Conclusions: Our findings inform the long-term conservation of a unique salamander genus. Strengthening conservation measures on Salamandrina species in areas predicted to become unsuitable or in areas that could become suitable and serve as ecological corridors will be critical. Furthermore, future monitoring efforts should focus on the corridors identified in the contact zone to assess whether the hybridization process is ongoing and at what rate.