Modelling competition and hybridization between native cutthroat trout and nonnative rainbow and hybrid trout.

Native salmonid fish have been displaced worldwide by nonnatives through hybridization, competition, and predation, but the dynamics of these factors are poorly understood. We apply stochastic Lotka-Volterra models to the displacement of cutthroat trout by rainbow/hybrid trout in the Snake River, Idaho, USA. Cutthroat trout are susceptible to hybridization in the river but are reproductively isolated in tributaries via removal of migratory rainbow/hybrid spawners at weirs. Based on information-theoretic analysis, population data provide evidence that hybridization was the primary mechanism for cutthroat trout displacement in the first 17 years of the invasion. However, under some parameter values, the data provide evidence for a model in which interaction occurs among fish from both river and tributary subpopulations. This situation is likely to occur when tributary-spawned cutthroat trout out-migrate to the river as fry. The resulting competition with rainbow/hybrid trout can result in the extinction of cutthroat trout even when reproductive segregation is maintained.

Predicting effects of hydrologic alteration and climate change on ecosystem metabolism in a western U.S. river.

We estimated past and future hydrographs and patterns of ecosystem metabolism in a fifth-order river of the western United States, where water use and climate change are both expected to alter hydrology in the immediate future. We first reconstructed the unregulated hydrograph to estimate how the current hydrograph has been altered. Due to consumptive use, 95% as irrigation, current discharge during summer (July-September) was 70% lower than would occur if the river was unregulated. We then predicted a future hydrograph including effects of consumptive use and climate change; the magnitude of flow changes were minor under this regime relative to those already manifested by consumptive uses. We used time-series regression and a six-year continuous record of open-water metabolism to demonstrate that, under the current hydrologic regime, gross primary production (GPP) was dependent on both water temperature and flow and that ecosystem respiration (ER) was most dependent on temperature. Monte Carlo simulations under the three hydrologic regimes and three temperature scenario's (current, +2 degrees C, +4 degrees C) suggested that flow, but not temperature, may have profound effects on the magnitude of metabolism. Linking temporally detailed analyses of ecological function and hydrology may lead to better understanding and management of changes due to basin-scale water use and/or global-scale climate change.