Flow regime, habitat configuration and functional traits influence distribution patterns in dynamic river networks

Metacommunity theory is an effort to explain species’ distributions at multiple scales, and is a potentially valuable tool for addressing such pressing issues as how species extinctions or invasions will influence riverine ecosystems.  We assume that patterns in the linked local communities of a river network emerge from interactions between the topology of its habitat template, as determined by flow regime and fluvial geomorphology, and the range of functional traits found in its species pool.  We develop a simple, generalized simulation framework to test predictions concerning these potentially complex interactions. In this model, physical habitat structure is captured as directed graphs composed of categorically classified nodes (reach and junction habitat), species are characterized in terms of their dispersal and reproductive capacities, and a flow/disturbance regime modifies these life history components by altering habitat quality.  We discuss results and implications of model runs examining whether greater γ-diversity occurs when 1) increased drainage density (as node degree) corresponds to a more divided network, 2) increased autocorrelation in flow sequence over both monthly and yearly cycles corresponds to reduced variance in site suitability, and 3) dispersal ranges are small relative to network dimensions and reproductive cycles are faster than flow-mediated disturbance cycles.