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Historical assemblage distinctiveness and the introduction of widespread non-native species explain worldwide changes in freshwater fish taxonomic dissimilarity

Authors

  • Aurèle Toussaint,

    Corresponding author
    1. CNRS, UPS, ENFA, UMR 5174 EDB (Laboratoire Évolution et Diversité Biologique), Université Paul Sabatier, Toulouse, France
    • Correspondence: Aurèle Toussaint, Laboratoire Evolution et Diversité Biologique (UMR 5174), Université Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse Cedex 4, France.

      E-mail: toussaint.aurele@gmail.com

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  • Olivier Beauchard,

    1. Netherlands Institute for Sea Research (NIOZ), Yerseke, The Netherlands
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  • Thierry Oberdorff,

    1. UMR IRD Biologie des Organismes et Écosystèmes Aquatiques BOREA 207, Département Milieux et Peuplements Aquatiques, Muséum National d'Histoire Naturelle, Paris, France
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  • Sébastien Brosse,

    1. CNRS, UPS, ENFA, UMR 5174 EDB (Laboratoire Évolution et Diversité Biologique), Université Paul Sabatier, Toulouse, France
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  • Sébastien Villéger

    1. Laboratoire Écosystèmes Marins Côtiers, UMR 5119 CNRS-UM2-IFREMER-IRD-UM1, Université Montpellier 2, Montpellier Cedex 5, France
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  • Editor: Janne Soininen

Abstract

Aim

Taxonomic dissimilarity between assemblages can result from two processes – the replacement of species (turnover) and differences in richness – but it remains unclear how anthropogenic drivers (introductions and extirpations) affect these processes. Here, we investigate how historical patterns and anthropogenic drivers shape the changes in dissimilarity and its turnover component in freshwater fish assemblages both in historical (i.e. pre-industrial) times and at the present day.

Location

World-wide.

Methods

We used a global database of fish assemblages in 1054 river basins throughout the world to quantify the change in turnover through its contribution to taxonomic dissimilarity between the two periods. We then used random forests to disentangle the relative roles of historical distinctiveness, species introductions and species extirpations on changes in dissimilarity and on the contribution of its turnover component.

Results

The pairs of basins exhibited a decrease in the contribution of turnover to taxonomic dissimilarity of 82% and 61% in homogenized and differentiated pairs, respectively. The historical number of shared species and its change after species introductions and extirpations accounted for more than 60% of the change in dissimilarity and in the turnover contribution in the six biogeographical realms.

Main conclusions

The historically high distinctiveness between pairs of basins, due to a low number of shared species, has promoted high levels of taxonomic dissimilarity. The world-wide changes in taxonomic dissimilarity among fish assemblages are to a large extent coupled to a decrease in the contribution of taxonomic turnover to taxonomic dissimilarity. Hence, the dissimilarity between assemblages declines with decreasing species replacement. These changes are mainly explained by introductions of a small set of widespread non-native species, which promote an increase in the number of shared species. Alongside historical distinctiveness, species introduction processes can determine whether assemblages become more homogenized or more differentiated. Our results suggest that taxonomic differentiation can quickly turn to homogenization as the number of species introductions increase.

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