How have European freshwater fish species changed over time?

Although all 251 river areas examined in the study exhibited a net species gain, species turnover was much higher than the net gain indicates. On average, one fifth of the historic fish assemblages became reshuffled. Species gains have led to an overall increase in similarity, or "taxonomic homogenization" across Europe, both in number of shared species as well as in species composition.

"The concurrent use of multiple indices allowed us to disentangle the main components of faunal change across Europe. In contrast to the established view, it is evident that the prevention of intended or unintended species introduction will not lower the increase in similarity per se: many species actually reduce homogenization despite their range gain, but still considerably contribute to taxonomic change with potential negative effects on ecosystem functions," said Dr. Nike Sommerwerk, lead author of the Journal of Biogeography study. "Such studies are important in identifying and implementing appropriate management strategies for species protection and biodiversity management."