Abstract
In running waters, under climate change conditions, the combined effect of water warming and decreasing flow rates may encourage colonisation by invasive cool and warm-water fish species. The aim of the study was to analyze the potential climate change effects on the spread of four invasive alien fishes in the Tiber River basin, taking into account the effects of river fragmentation. Fish and environmental data collected in 91 sites over the years 1998–2018, were used to analyze temporal changes in their habitat requirements. A multivariate analysis was conducted, and the hypothesis of a range expansion towards the upstream reaches has been tested. For Barbus barbus, Gobio gobio, Padogobius bonelli and Pseudorasbora parva population abundances and body condition were analyzed. Detectability, occupancy, local extinction and colonization probabilities were estimated. We showed that B. barbus and P. bonelli have significantly extended their range toward upstream. P. parva did not move toward higher altitudes significantly, suggesting that, at this stage, the species has probably reached an equilibrium. River fragmentation, elevation, water temperature and average current speed seem to be major determinants in colonization processes, affecting the dispersal ability of the species. Not surprisingly for species introduced in relatively recent times, the colonization probabilities were much higher than extinction probabilities. Our results provided evidence for some synergistic effects between climate changes and alien fish species invasions, in terms of species range shifts mediated by rising water temperatures, although they should be interpreted cautiously, taking into account that these species most likely were not yet stabilized.
Highlights
The populations of P. bonelli were mainly circumscribed in the upper part of the Tiber river basin, where its introduction occurred 27 years ago, even if the sporadic presence of the species has been recently detected in the mountain portion of a left tributary, the Chiascio river; for P. bonelli it was possible to notice how the most abundant populations distinguish, above all, the most recent census period (Figure 2c)
For P. bonelli the number of occurring sites remained quite stable and equal to 12 and 13 in the first two census periods, respectively, while an increase of 5 sites was observed in more recent years (Figure 3c)
Our results provided some evidence for synergistic effects between climate change effects and alien cool-water adapted species invasions
Summary
The aim of the study was to analyze the potential climate change effects on the spread of four invasive alien fishes in the Tiber River basin, taking into account the effects of river fragmentation. P. parva did not move toward higher altitudes significantly, suggesting that, at this stage, the species has probably reached an equilibrium. Our results provided evidence for some synergistic effects between climate changes and alien fish species invasions, in terms of species range shifts mediated by rising water temperatures, they should be interpreted cautiously, taking into account that these species most likely were not yet stabilized. The progressive rise in water temperature as a result of global warming may encourage colonization by invasive alien species whose expansion would otherwise be limited by low temperatures [4,7,8]
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