Long-term detection data reveals widespread range contractions in Spanish herpetofauna

Populations of amphibians and reptiles have undergone substantial declines in recent decades worldwide. The Iberian Peninsula, a European diversity hotspot for this group, is suffering severe droughts, rising temperatures, and abandonment of traditional agricultural practices. Despite the importance and sensitivity of Iberian herpetofauna, a data-driven, national, long-term, and multi-species analysis of the distribution and demographic situation of amphibians and reptiles has been lacking. We used dynamic occupancy models to study how the distributions of 25 amphibian and 37 reptile species have changed over the last three decades in Spain. We analysed a detection dataset compiled from multiple sources including citizen science, monitoring programmes and opportunistic observations. Our results showed widespread declines in amphibian and reptile occupancy, which could also suggest generalised population declines. Moreover, we observed a mismatch between the IUCN Red List categories and the estimated occupancy trend, with some species appearing stable at the IUCN global level but presenting substantial range contractions at the regional level. The causes for these declines are unclear. According to our models, amphibian persistence was negatively correlated with rainfall and colonization negatively correlated with altitude. Reptile persistence was negatively correlated with temperature. Our analysis highlights the value of national-scale assessments to identify occupancy trends at fine resolution and investigate regional threats driving these changes. We encourage further research and early conservation action before regional trends and threats become global issues. We further highlight the need for long-term, standardized monitoring programmes to contribute high-quality data to regional and global assessments.