A multi-temporal approach to model endangered species distribution in Europe. The case of the Eurasian otter in Italy

We analyzed the relationship between changes in land cover patterns and the Eurasian otter occurrence in southern Italy over the course of approximately 20 years (1985–2006) using multi-temporal species distribution models (SDMs). The study area includes five river catchments covering most of the otter's Italian range. Land cover and topographic data were used as proxies for the ecological requirements of the otter within a 300-m buffer around river courses. We used species presence, pseudo-absence data, and environmental predictors to build past (1985) and current (2006) SDMs by applying an ensemble procedure through the BIOMOD modeling package. The performance of each model was evaluated by measuring the area under the curve (AUC) of the receiver-operating characteristic (ROC). Multi-temporal analysis of species distribution was performed by comparing the maps produced for 1985 and 2006. The ensemble procedure provided good overall modeling accuracy, revealing that elevation and slope affected the otter's distribution in the past; in contrast, land cover predictors, such as cultivations and forests, were more important in the present period. During the transition period, 20.5% of the area became suitable, with 76% of the new otter presence data being located in these newly available areas. The multi-temporal analysis suggested that the quality of otter habitat improved in the past 20 years due to the expansion of forests and to the reduction of cultivated fields in riparian belts. This evidence stresses the great potential of riverine habitat restoration and environmental management in supporting the future expansion of the otter in Italy.