Long term persistence, density dependence and effects of climate change on rosyside dace (Cyprinidae)
SUMMARY 1. We used long term population data for rosyside dace (Clinostomus funduloides) a numerically dominant member of a stochastically organised fish assemblage, to evaluate the relative importance of density dependent and density independent processes to population persistence. 2. We also evaluated the potential impacts of global climate change (GCC) on this species and predicted how directional environmental changes will affect dace. 3. We sampled two 30 m permanent sites in spring and autumn in the Coweeta catchment for rosyside dace density using three pass electrofishing between 1984 and 1995, and a single 100 m site from 1991 to 2003. 4. Habitat availability and flow variation data for this 20 year period demonstrated that two droughts (1985 1988 and 1999 2002) produced smaller wetted areas, lower mean, maximum and minimum flows, fewer high flow events and greater amounts of depositional substrata in the sites. 5. Droughts produced significant increases in abundance, and significant decreases in standard length and mass of rosyside dace. Increases in abundance were mainly due to increased survival/ immigration of young of the year (YOY) 6. Model selection analysis using multiple single and multivariable models indicated that density dependence in various forms possessed substantial explanatory power with respect to long term variation in the per capita rate of increase (r) in all sites and seasons. Density dependent effects on r were stronger in autumn than spring, whereas negative density independent models (flow variation) had the greatest explanatory power in spring. 7. Results for growth data were similar to those for rosyside dace density and confirm density dependence likely through intraspecific competition for food or foraging sites leading to reduced growth at higher densities. 8. These data support the hypothesis that species may persist in stochastic animal assemblages via strong intraspecific density dependence. Greater flow variability or increased high flows produced by GCC may destabilise this population leading to reduced compensation and possibly eventual extinction.