An evaluation of the relative influence of spatial, statistical, and biological factors on the accuracy of stream fish species presence models

Models relating fish species presence to landscape and stream features are increasingly being used by natural resource managers. The accuracy of these models directly influences the ability to make sound stream management decisions. To evaluate the effect of biotic and abiotic factors on model accuracy, I fit parametric (logistic regression) and nonparametric (k-nearest neighbor) models of species presence at two spatial scales using watershed and stream reach characteristics. I then evaluated the influence of model type, spatial scale, and species-specific traits, on the cross validation errors of the 4 best-fitting scale-specific, parametric and non parametric models. I found that errors were highly variable within a species and error rates were related to model type, spatial scale, and species-specific traits. Findings from this study suggest that species specific traits had a large effect along with the effects of scale and that resource managers should consider these effects when modeling presence or absence of fish species.