Riverine Landscapes: Exploring Connectivity, Extinction Risk, and Biogeography in an Alternative Geometry

Riverine landscapes differ in fundamental ways from terrestrial ones. In particular, the branching hierarchical geometry and downstream flow of river systems lead to a suite of network properties rarely considered in 2-dimensional systems that have long been the mainstay of landscape ecology. Intrinsic effects of configuration, directional biases, transient connectivity, and opportunities for ‘out of network’ movement may all lead to inherently asymmetrical opportunities for connections among parts of a riverine landscape thereby influencing ecological processes and biogeographic patterns. This ‘alternative geometry’ of riverine networks provides excellent opportunities for scientists to explore how network connectivity shapes habitat occupancy, metacommunity dynamics, and biogeographic patterns. Using examples involving fish communities that inhabit the river networks of North America and India, I will discuss here how human modifications to the spatial characteristics of river systems, such as habitat fragmentation and interbasin water transfer projects, influence ecological dynamics and biogeographic patterns. Taken together these research projects illustrate the important contributions that riverine geometry makes to our understanding of interspecific variation in extinction risks and the potentially broad relevance of the neutral theory of biodiversity.