Topographic controls on divide migration, stream capture, anddiversification in riverine life

Abstract. Drainages reorganise in landscapes under diverse conditions and process dynamics. We investigated the relative control that Earth surface process parameters have on divide migration and stream capture in scenarios of base level fall and heterogeneous uplift. A model built with the Landlab toolkit was run 51,200 times in a sensitivity analysis that used globally observed values. Large-scale drainage reorganisation occurred only in the model runs within a limited combination of parameters and conditions. Uplift rate, rock erodibility, and the magnitude of perturbation (base level fall or fault displacement) had the greatest influence on drainage reorganisation. The relative magnitudes of perturbation and topographic relief limited landscape susceptibility to reorganisation. Stream captures occurred more often when the channel head distance to divide was low. Stream topology set by initial conditions strongly affected capture occurrence when the imposed uplift was spatially heterogeneous. We also modelled riverine species lineages as they developed in response to the single topographic perturbation. We used a new Landlab component called SpeciesEvolver that models species lineages at landscape scale. Simulated species populated to the modelled landscape were tracked and evolved using macroevolutionary process rules. More frequent stream capture and less frequent stream network disappearance due to divide migration increased speciation and decreased extinction, respectively, in the heterogeneous uplift scenario where final species diversity was often greater than the base level fall scenario. Under both scenarios, the landscape conditions that led to drainage reorganisation following a single perturbation also controlled diversification, especially for the species that evolved more rapidly in some model trials. These results illustrate the utility of SpeciesEvolver to explore how life evolves alongside landscapes. Future research applications of SpeciesEvolver can incorporate more complex climatic and tectonic forcings as they relate to macroevolution and surface processes, as well as region- and taxon-specific organisms based in rivers as well as those on continents at large.