Fine-scale habitat preferences of riparian ectotherms in a human-influenced landscape: insights from two herptiles endemic to the Iberian Peninsula

Abstract Riparian ecosystems support diverse ecological functions and species. Despite their importance, these areas are increasingly threatened by human activities. In the Iberian Peninsula, the extensive anthropisation of the landscape has a strong influence on the quality of riparian zones, impacting species that depend on these habitats. We aim to understand the occupancy drivers of an amphibian, Chioglossa lusitanica , and a reptile, Lacerta schreiberi , typically associated with riparian habitats, to assess levels of habitat fragmentation and evaluate their relative importance and complementarity as bioindicators of riparian habitat degradation. Sampling was conducted in the Ceira River watershed (505 km²) in central Portugal, involving 140 sites across three campaigns. Covariates related with terrain, land-use, vegetation, human disturbance, and climate were used to model species occupancy using Bayesian methods. Landscape metrics were calculated from model predictive maps to evaluate and compare habitat fragmentation. The model for C. lusitanica included only terrain variables (Elevation, Insolation, and Valley Depth) as significant predictors. For L. schreiberi , the best-supported model included Valley Depth, Traditional Crops Cover, Human Footprint Index, and Tree Cover Loss. A sympatry of 20.6% (occupancy threshold = 0.8) was found between the species, with L. schreiberi showing significantly higher fragmentation. L. schreiberi can serve as a bioindicator of riparian habitat quality, as it tends to respond more markedly to human disturbance gradients than C. lusitanica , which is more related with microclimate conditions and stream hydrology. Combined data from both species may contribute to more effective conservation strategies and highlight the urgency of preserving riparian ecosystems.