1. Department of Civil and Environmental Engineering, E-Quad, Princeton University, Princeton, New Jersey 08544, USA
2. Laboratory of Ecohydrology, Faculté ENAC, École Polytechnique Fédérale, CH-1015 Lausanne, Switzerland
3. Department of Biology, University of Maryland, College Park, Maryland 20742, USA
4. Dipartimento di Ingegneria Idraulica, Marittima, Ambientale e Geotecnica (IMAGE) and Centro Internazionale di Idrologia 'Dino Tonini', Università di Padova, via Loredan 20, I-35131, Padua, Italy

Correspondence to: Rachata Muneepeerakul¹Ignacio Rodriguez-Iturbe¹ Correspondence and requests for materials should be addressed to R.M. (Email: rmuneepe@princeton.edu) or I.R.-I. (Email: irodrigu@princeton.edu).

River networks, seen as ecological corridors featuring connected and hierarchical dendritic landscapes for animals and plants, present unique challenges and opportunities for testing biogeographical theories and macroecological laws¹. Although local and basin-scale differences in riverine fish diversity have been analysed as functions of energy availability and habitat heterogeneity², scale-dependent environmental conditions³ and river discharge^{4, 5}, a model that predicts a comprehensive set of system-wide diversity patterns has been hard to find. Here we show that fish diversity patterns throughout the Mississippi–Missouri River System are well described by a neutral metacommunity model coupled with an appropriate habitat capacity distribution and dispersal kernel. River network structure acts as an effective template for characterizing spatial attributes of fish biodiversity. We show that estimates of average dispersal behaviour and habitat capacities, objectively calculated from average runoff production, yield reliable predictions of large-scale spatial biodiversity patterns in riverine systems. The success of the neutral theory in two-dimensional forest ecosystems^{6, 7, 8} and here in dendritic riverine ecosystems suggests the possible application of neutral metacommunity models in a diverse suite of ecosystems. This framework offers direct linkage from large-scale forcing, such as global climate change, to biodiversity patterns.