Drivers of biodiversity and invasion in the aquatic and riverine communities of three river systems in Mississippi, USA

River ecosystems and their plant communities are a critical component to the landscape of Mississippi and invasion represents a substantial threat to these systems. This study focused on the Pascagoula River, the Pearl River, and the Tennessee-Tombigbee Waterway, whose hydrology range from largely unaltered to highly altered. The rivers’ aquatic and riverine communities were measured using point surveys and site community compositions were assessed using nonmetric multidimensional scaling (NMDS). We found that sites on the Pascagoula and Pearl rivers were similar to each other while being dissimilar to the TTW sites, and that coastal systems on the Pascagoula and Pearl Rivers separated from the noncoastal sites. The effects of latitude and river system on species sample richness ( s ) were assessed using a linear mixed-effects model. The effects of latitude and native species richness ( s n ) on the presence/absence of introduced species ( pa i ) were assessed using a generalized linear model. Results showed that across all river systems, decreasing latitude increased s . These results suggest that although these rivers have differences in their community composition, the effect of latitude on s is strong enough to be exhibited consistently in all three rivers. Additionally, we found that s n (positive) and latitude (negative) had substantial effects on pa i with s n being the stronger predictor. These findings are consistent with the well-supported “rich get richer” hypothesis that posits a positive relationship between native plant richness and introduced plant richness. This pattern describes the broad and indirect association between native species richness and susceptibility to invasion.