Native Congener Richness, Not Abiotic Factors, Predicts Cyprinid Introductions

Because their distributions are naturally limited by catchment boundaries, stream fishes make excellent model taxa for examining the mechanisms that drive invasions. We compared the importance of abiotic and biotic predictors of native and nonindigenous minnow richness in 168 catchments throughout the eastern United States. We determined historic (baseline) cyprinid distributions data from NatureServe, and contemporary distributions from state stream fish community sampling programs. Temperature, elevation, precipitation, land use, and human population density data were obtained from a variety of public sources. We used generalized linear mixed models in an information-theoretic framework to identify predictors of native and nonindigenous cyprinid richness at the catchment scale. Native richness was affected most importantly by latitude, and more weakly by temperature stability and average precipitation. Native congener richness was by far the most important predictor of nonindigenous cyprinid richness; 95% confidence intervals of all abiotic factors bounded zero. Our results provide no support for biotic resistance or Darwin’s naturalization hypothesis. At this spatial scale, trait preadaptation may be more important than intrageneric competition for nonindigenous species establishment. The lack of importance of abiotic features suggests that prioritizing catchments for prevention and control of nonindigenous cyprinids will be complicated.