Lagarde R. auteur aut IRD Teichert N. auteur aut IRD Valade P. auteur aut IRD Ponton Dominique auteur aut IRD text journalArticle eng text/pdf born digital access Determining the relative importance of niche- and dispersal-based processes in the structuring of animal communities is central in ecology. Freshwater fish and crustacean communities of small tropical islands can bring new insights for understanding these processes as all their species present a pelagic larval stage which gives them important dispersal capacities. Consequently, we hypothesized that dispersal-based process may be preponderant for structuring these communities from the regional to the local, that is, survey site, scales. Gradient forest analyses allowed us to model the effect of 12 environmental variables on freshwater taxa abundances in two southwestern Indian Ocean islands: Mayotte (26 taxa) and Reunion (21). A total of 153 surveys in Mayotte and 266 in Reunion were used for building the models. Despite the strong heterogeneity of environmental conditions between the two islands, the main factors structuring freshwater fish and crustacean communities in both islands were the elevation and the slope of the sites. The observed structure appeared more pronounced for predatory species than for primary consumers and omnivores. As predators generally have limited locomotor capacities, it is concluded that dispersal-based process structures these communities not only at large geographical scales but also at the intra-watershed scale, by limiting the inland penetration (or dispersion) of species in relation to their locomotor capacities. However, more knowledge concerning ecological traits and taxonomic status of many species is needed to confirm this assumption. in French is available with online material specialized abundances diadromy environmental gradients migration taxonomic richness western Indian Ocean OCEAN INDIEN ZONE TROPICALE 034 53 1 243-254 2021 0006-3606 https://www.documentation.ird.fr/hor/fdi:010079932 10.1111/btp.12865 0006-3606 [F B010079932] https://www.documentation.ird.fr/hor/fdi:010079932 https://www.documentation.ird.fr/intranet/publi/2020/11/010079932.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2020-12-08 2025-02-24 fdi:010079932 fre