How flow speed alters competitive outcome in advective environments.

Many species live in advective environments, such as rivers or streams. The community composition in such environments is shaped by the interplay between biotic interactions and hydrologic constraints. Lutscher et al. (Theor. Popul. Biol. 71:267-277, 2007) demonstrated by simulation that advective flow can shift competitive outcome from one species dominating to coexistence or even to the other species dominating. Here, we present a detailed analysis of the Lotka-Volterra advection-diffusion model underlying their simulations. We use variational techniques as well as a spatially implicit approximation to determine all possible advection-induced shifts in competitive outcome. We show that changes in advection follow relatively few and predictable paths. We illustrate our results in various bifurcation diagrams.