Predicting global change impact on invasive alien species’ distribution: case study for variable squirrel (Callosciurus finlaysonii) in Italy

Callosciurus finlaysonii (variable squir- rel) is indigenous to Southeast Asia and is included in the list of Invasive Alien Species of Union Con- cern. In Southern Italy, it has expanded its range following its release in the 1980, posing a potential threat to autochthonous plants and animals. In this study, we elucidated how range and population via- bility will vary under different global change future scenarios, by using a comprehensive framework com- bining spatial analyses and demographic dynamics based on occurrence. Analyzing the time frame from release thus far, we revealed that the available habi- tat for variable squirrel exceeds the current colonized range, spreading predominantly in the coastal areas and human settlements. The four hypothetical future scenarios we tested project a similar initial increase in population size, although they are based on Shared Socioeconomic Pathways differing in terms of energy development and global conflicts, and indirectly on warming. If the variable squirrel continues its expansion, it could be represent a threat for the Ital- ian native black squirrel (Sciurus meridionalis). We suggest that the management of the variable squir- rel should be addressed considering the dynamics of expansion and habitat occupancy from its release to the future, acting with an eradication program right now, anticipating a more rapid and worrying expansion.