The spatial arrangement of stream networks influences community dynamics; therefore the functional diversity and beta diversity of headwater fish assemblages may be altered in relation to environmental and spatial factors. As agents of habitat fragmentation, the presence of large-scale impoundments and changing patterns in land use may alter the predicted importance of hydrologic coarse-scale factors on dispersal, causing shifts in stream fish community structure and composition. In this study, we use functional metrics and compositional data to distinguish how functional diversity and beta diversity change in relation to environmental and anthropogenic gradients at coarse spatial scales. We conducted our study in the Little Tallahatchie River system, which is positioned within the upper Yazoo River basin in North-Central Mississippi. We tested the predictions that (1) changes in beta diversity and functional diversity will be driven by habitat filtering along a stream-size-connectivity gradient and (2) the extent to which this environmental gradient drives community dynamics will be regulated by the proportion of anthropogenic land use or the proximity of a site to Sardis reservoir. We used ordination techniques (CCA) to examine the relationships between environmental and anthropogenic variables on the functional diversity and beta diversity of headwater fish assemblages.
Results/Conclusions
Differences in fish metrics were primarily driven by changes in downstream link (D-Link) and the proportion of anthropogenic land use (ALU) within a site’s upstream catchment. D-Link had the strongest scores along the CCA 1 axis, accounting for 9.25% of the variance. ALU had the strongest scores along the second axis, which resulted in describing 3.69% of the variance. The final model explained a significant amount of the variation (p < 0.01), and both variables explained a significant portion of the variance (p < 0.05). Differences in community composition were driven by changes in confluence link (C-Link) and ALU. C-Link had the strongest scores along the CCA 1 axis, which described 5.75% of the variation. ALU possessed the strongest scores along the second axis, and described 4.5% of the constrained variation. The final model explained a significant amount of the variation (p < 0.05). C-Link described a significant amount of the variance (p < 0.05). The functional diversity and beta diversity of headwater fish assemblages within the Little Tallahatchie River system appear to be driven by a stream-size-connectivity gradient, but the strength of this environmental gradient may be altered as a result of changing patterns in land use.