Come back to stay: landscape connectivity analysis for the Eurasian otter (Lutra lutra) in the western Alps

Assessing landscape connectivity allows defining the degree to which the landscape facilitates or impedes the movement of a species between resource patches. In this phase of climate change and biodiversity crisis, maintaining landscape connectivity by restoring and protecting connecting areas and corridors is a key strategy to ensure the survival of many species. The Eurasian otter (Lutra lutra) is a freshwater top predator that is slowly recovering after a dramatic decline occurred in central and southern Europe in the last century. To assess the chances of otter recolonization of the western Alps, we analyzed environmental connectivity by applying electrical circuit theory to an expert-based resistance surface using the Circuitscape software. The study area included southeastern France, northwestern Italy, and Switzerland. We produced a cumulative current flow map and a gap analysis was also conducted to highlight the "conservation gaps" for optimal corridors. The results revealed that the orography of the landscape was the main factor influencing the quantity and quality of the pathways in the western Alpine landscapes. As main corridors were concentrated on valley bottoms, human pressure could severely diminish animal movement. Despite this, some heavily populated areas showed high connectivity values. Some important pathways did not fall within protected areas, potentially hindering otter dispersal and highlighting the need to expand the system of protected areas in the Alpine arc. Recolonization of Alpine territories by otters can therefore only occur if connectivity and environmental suitability combine to ensure the animals' survival over time.