Taxonomic and functional diversity patterns reveal different processes shaping European and Amazonian stream fish assemblages

AimDifferences in dispersal limitation and environmental filtering have been proposed to explain differences in diversity patterns between regions. Incorporating functional traits into studies of assembly rules allows the relative strengths of such processes to be distinguished. We test the predictions that assemblages in a similar environment under strong dispersal limitation should be differentiated taxonomically but not functionally, whereas strong environmental filtering should more differentiate assemblages functionally. LocationFrench Guiana and France. MethodsWe used two datasets on fish assemblage composition: one for French Guiana and one for continental France. We constrained both dataset to have similar geographical extent and similar environment using site location and topographic variables of the French Guiana dataset to select continental France data. We estimated functional diversity using a combination of 15 fish morphological traits. We computed species and functional richness at regional and local scales for both regions. We calculated taxonomic and functional turnover between sites and compared them within and between regions. ResultsTaxonomic and functional richness were higher in tropical fish assemblages than in temperate ones both on regional and local scales. Species richness differences between the two regions resulted in very similar functional richness. Temperate assemblages showed a higher functional turnover than tropical assemblages, but a lower taxonomic turnover. We found a stronger turnover in taxonomic diversity than in functional diversity between tropical assemblages, and the opposite pattern between temperate ones. Main conclusionsThe higher functional richness in tropical assemblages was mainly caused by an increased number of species compared to temperate assemblages, probably linked with an increase in available niches. Dispersal limitation was the predominant process in structuring Guianese stream fish assemblages causing strong species replacement, whereas French stream fish assemblages were mainly under strong environmental filtering resulting in local adaptations to different environments.