Endemic Freshwater Fish Range Shifts Related to Global Climate Changes: A Long-Term Study Provides Some Observational Evidence for the Mediterranean Area

Climate changes will lead to a worsening of the ecological conditions, in terms of hydrological instability and rising water temperatures, of the Mediterranean rivers. Freshwater fishes inhabiting this area can be threatened in the near future by accelerating drought and decreased ecological connectivity. The main aim of the research was to analyze changes in the distribution of the endemic freshwater fishes Padogobius nigricans, Squalius lucumonis and Telestes muticellus in the Tiber River basin (Italy), within a proven period of climate warming, in terms of increasing water temperature and droughts. A multivariate analysis was conducted using fish and environmental data collected in 117 sites over the years 1990–2017. For the three species, population abundance, age structure and body condition were analyzed. Detectability, occupancy, local extinction and colonization processes were also examined. We showed that S. lucumonis and T. muticellus have shifted their distributions upstream, likely in order to reach their thermal optimum. Padogobius nigricans did not move upstream significantly, since the species is characterized by limited vagility and thus a low dispersal capability in a context of high river fragmentation. In the study area, elevation and river barriers seem to play a key role in extirpation and colonization processes; for S. lucumonis and T. muticellus the extinction probability decreased with increasing altitude, while for P. nigricans the colonization probability decreased with an increasing degree of river fragmentation. These results highlight how species-specific dispersal ability can lead to varying adaptability to climate change.