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Drainages reorganise in landscapes under diverse conditions and process dynamics that impact biotic distributions and evolution. We first 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 sensitivity analyses 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 integrated simulations of geomorphic and biologic processes to investigate relationships among topographic relief, drainage reorganisation, and riverine species diversification in the two scenarios described above. We used a new Landlab component called SpeciesEvolver that models species at landscape scale following macroevolutionary process rules. More frequent stream capture and less frequent stream network disappearance due to divide migration increased speciation and decreased extinction, respectively, especially in the heterogeneous uplift scenario in which final species diversity was often greater than the base-level fall scenario. Under both scenarios, the landscape conditions that led to drainage reorganisation also controlled diversification. Across the model trials, the climatic or tectonic perturbation was more likely in low-relief landscapes to drive more extensive drainage reorganisation that in turn increased the diversity of riverine species lineages, especially for the species that evolved more rapidly. This model result supports recent research on natural systems that implicates drainage reorganisation as a mechanism of riverine species diversification in lowland basins. Future research applications of SpeciesEvolver software can incorporate complex climatic and tectonic forcings as they relate to macroevolution and surface processes, as well as region- and taxon-specific organisms based in rivers and those on continents at large. [ABSTRACT FROM AUTHOR]

To better understand how climate affects bedrock river incision and long-term landscape evolution in the absence of tectonic forcing, we quantify differences in the longitudinal profiles of eroding bedrock channels across the Kohala peninsula on the northern tip of the Big Island of Hawai'i. An orographic rainfall gradient causes mean annual precipitation rates to vary by over an order of magnitude, from greater than 4000 mm/yr on the wet side to less than 250 mm/yr on the dry side of the peninsula. Channels on the wet side are relatively deeply incised into the surrounding landscape and have developed profiles in which slope increases downstream in upstream reaches (convex form) and de- creases downstream in downstream reaches (concave form). Wet-side river channels have relatively large (10-30 m) vertical steps, or knickpoints, in the convex zone. In contrast, channels on the dry side of the peninsula are more shallowly incised, have developed nearly straight longitudinal profiles in which channel slope does not significantly change from upstream to downstream, and have smaller knickpoints. Channel profile form changes from straight to convex-concave at a watershed-averaged mean annual precipitation rate of between ~1300 and 1750 mm/yr, suggesting a climatic threshold in this landscape, above which bedrock incision rates are enhanced. Valley depth (used as a proxy for the magnitude of channel incision) increases with increasing mean annual precipitation and is consistent with a similar fluvial-incision threshold. While the lithology is entirely basalt, incision patterns also appear to be affected by spatial differences in bedrock weathering due to both local climate and basalt flow age. The older and more weathered Pololu basalts (260-450 ka) are capped by the younger Hawi basalt series (120-260 ka), and we interpret that heterogeneous weathering of these units influences channel form, relief, sediment production, and knickpoint development. [ABSTRACT FROM AUTHOR]