Environmental correlates with fish assemblage change and biotic homogenization across 40 years in an Ozark, Gravel-Bed river basin

Fish assemblages in freshwater ecosystems are becoming more homogenous from multiple abiotic, environmental, and physicochemical variables at different scales. Historical fish collections (1976–1977) by Billy Michael Johnson and Dr. Johnson K. Beadles were compared to contemporary fish collections (2018–2019) in tributaries of the Eleven Point River basin in Arkansas to examine patterns of fish assemblage change. Fish assemblage change variables were compared to pasture land use/land cover (LULC) at multiple scales and in-stream habitat variables to understand relationships and discover potential correlates suggesting biotic homogenization. Fish assemblages in the Eleven Point River basin of Arkansas have experienced significant spatiotemporal changes, and LULC change and habitat alterations may have influenced this process. Increased tolerant species and decreased intolerant species at sites contributed to biotic homogenization, particularly in pool habitats. Surprisingly, expansion of some intolerant fishes was also observed that tend to occupy riffles. Sites with high percentages of pasture LULC at finer spatial scales typically had more homogenised fish assemblages. We hypothesized gravel aggradation from local pasture land use has degraded pools and increased riffle habitat, resulting in homogenised fish assemblages in the Eleven Point River basin over the study period. Few studies link LULC, in-stream habitat, and biotic homogenization when examining fish assemblage change over time, and these dynamics can be particularly complex in upland streams experiencing gravel aggradation. Similar research in other upland, gravel-bed river systems would provide a broad understanding of the presented environmental associations.