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Freshwater fish diversity in heavily invaded ecosystems (Po River Basin, Italy)
The introduction of non-native species is a global phenomenon and a major driver of biodiversity loss and community homogenisation, particularly in freshwater ecosystems. How the functional and taxonomic diversity of freshwater communities responds to the presence of non-native species is still a matter of debate and requires further investigation. In this context, fish communities in impacted rivers, which are highly vulnerable to the introduction of non-native species, provide an excellent model to study these dynamics.
In this study, a comprehensive dataset from 335 Mediterranean rivers and streams was analysed to investigate the relationships between functional and taxonomic diversity and the presence of non-native species. Results showed that lower functional diversity in total fish communities was associated with higher levels of invasion, and that the non-native component of fish communities exhibited less diverse functional traits compared to native ones, even when stream order was considered. Hotspots of non-native species with low functional diversity were predominantly located in human-disturbed areas, suggesting a significant role of human disturbance in invasion patterns.
Further analysis of functional uniqueness showed a decreasing trend in overall fish community uniqueness with increasing stream order. Interestingly, native species exhibited high functional uniqueness in disturbed canals, whereas non-native species exhibited the highest uniqueness in the lowest stream order ecosystems. These results highlight the importance of assessing native and non-native components of biotic communities separately to better understand the links between invasion dynamics and biodiversity loss.
