Taxonomic and functional homogenization of fish assemblages in an Ozark river associated with pasture land use and constructed water bodies

Comparisons between contemporary and historic surveys are useful in assessing how fish assemblages respond to anthropogenic stressors. When these stressors degrade aquatic environments, assemblages often experience biotic homogenization. The Strawberry River flows through the Ozarks of northern Arkansas and has been subject to both pasture land use conversion and constructed waterbodies which can degrade aquatic environments and alter fish assemblages. We investigated how fish assemblages in the Strawberry River have changed over a 35-year time span in response to pasture land use and constructed waterbodies. We found evidence of both taxonomic and functional homogenization of fish assemblages from the mid-1980s to 2019. This shift towards homogenization was primarily driven by increases in both site occurrence and abundance of generalist centrarchid species (associated with land use practices) and headwater specialist species (likely related to increased intermittency upstream). We created a composite variable using principal component analysis that represented pasture land use and constructed water body metrics because of their close relationship with each other. We found evidence of early functional differentiation associated with this composite variable; however, we found that over time fish assemblages ultimately experienced greater levels of homogenization associated with this same variable. This pattern of biotic homogenization associated with species additions suggests the Strawberry River is at a tipping point along a subsidy stress gradient, and in the future, we expect to see losses of specialist endemic species if conservation actions are not taken.