1 American Fisheries Society Symposium 73:000–000, 2010 © 2010 by the American Fisheries Society Community Ecology of River Fishes: A Large-Scale Perspective Bernard Hugueny*, Thierry Oberdorff, and Pablo A. Tedescco UMR BOREA, Département Milieux et Peuplements Aquatiques MNHN, CNRS 7208, IRD 207, UMPC, Muséum National d’Histoire Naturelle, 43 rue Cuvier, 75231 Paris, France Abstract.—Community ecology increasingly seeks to integrate the influences of regional and historical processes with species interactions within local habitats. is broadened perspective is largely based on comparative approaches that employ “natural experiments” to identify factors shaping community structure. Because coastal rivers are separated from one another by insurmountable barriers (oceans or land), freshwater fishes are particularly well suited for comparative analyses of factors that influence fish community organization. In this chapter, we review how this comparative approach shed light on large-scale biodiversity gradients, com- munity saturation, community convergence, density compensation, and the role of intrinsic and extrinsic factors in community dynamics. e main factors (e.g., river mouth discharge and history) empirically related to species richness of a river are well identified, and metacommunity ecology provides a fruitful conceptual framework for understanding how regional (river) species richness translates into local species richness. Much work remains to identify factors explaining differences among whole river basin assemblages with regard to ecological traits (e.g., trophic status and life history) composition and to assess whether trait-related environ- mental and biotic local filters act similarly over large spatial scales. One important conclusion that can be drawn from the studies reviewed here is that history cannot be neglected whatever the scale of investigation (global, river, or site). A second conclusion is that historical effects are not strong enough to blur the occurrence of qualitatively repeatable paerns of community structure over large spatial scale, which is encouraging because it suggests development of general predictive models of community structure is an aainable goal. * Corresponding author: hugueny@mnhn.fr Introduction Ecology is an integrative science that inves- tigates processes operating at levels from in- dividual organisms (e.g., behavioral ecology) to the entire biosphere (e.g., biogeochemical cycles) over time scales ranging from a few seconds (e.g., prey choice) to centuries (e.g., ecosystem succession). However, many eco- logical studies are conducted at local scales (<1 km 2 ) and during short periods (<3 years) (Blackburn and Gaston 2003). Of course, lo- gistical constraints largely explain this bias to- ward small-scale investigations; yet, within the field of community ecology, there has been a long-held view that communities are strongly influenced by species interactions operating within habitats. is “theory of local diver- sity” (Schluter and Ricklefs 1993b) states that