Patterns of fish invasions in the Great Plains of North America

A basic step toward controlling invasive species outbreaks is to predict which assemblages or habitats are most susceptible to invasion and effects of invading species on native communities. However, because predictive models may not work across a wide range of conditions it is important to examine processes associated with fish invasions across different regions. In this study, we use data from 949 sites in Oklahoma and Kansas to examine spatial patterns of species invasions in the Great Plains region of the US. Of these sites, 16 were intensively sampled between 1977 and 1994 and used to evaluate temporal patterns of species introductions. We found a trend of increasing introduced species richness without a decline in native species richness over 18 years. However, total abundance and community structure of native assemblages has changed at several of these sites during this time period. Because some of these changes occurred at sites with few or no introduced species, factors other than interactions with introduced fishes may have been responsible for this pattern. A stepwise multiple regression model that included human population size, native species richness, mean annual precipitation and drainage area explained 43% of the variation in the number of non-native species across all sites. Most introduced species in this region have native ranges within the Mississippi River basin and therefore are presumably adapted to regional environmental conditions. Great Plains streams have, to some extent, resisted invasion by introduced species; however, our analysis shows that proximity to dense human populations and importance to humans has largely structured species introductions and can partly explain spatial patterns of species invasions in this region.