Hierarchy theory reveals multiscale predictors of Arkansas darter (Etheostoma cragini) abundance in a Great Plains riverscape

Abstract

Abstract Landscape ecology and its emphasis on relationships between spatial heterogeneity, scale, and ecological processes can be applied to manage stream ecosystems as riverscapes. Hierarchy theory, a central tenet of riverscape ecology, allows for investigating ecological relationships between aquatic organisms and habitat by exploring the nested interactions inherent in reaches, segments, and basins. Arkansas darter Etheostoma cragini is a Great Plains fish endemic to the Arkansas River basin and is listed as in need of conservation in all five states within its range in North America. The aim of this study was to develop empirical models describing relationships between Arkansas darter abundance and local habitats, and identify the appropriate scale(s) for assessing and managing populations. We used Arkansas darter abundance data collected from stream sample units as a fixed grain size (102 m) and compiled datasets at three hierarchical spatial extents, including reach (103 m), nested within segment (104 m), nested within basin (105 m) in southcentral Kansas. We fit generalised linear mixed models (GLMMs) to assess scale‐specific relationships between Arkansas darter abundance and local habitat dimensions (stream depth and width) and heterogeneity (canopy cover, overhanging vegetation, and woody structure). Habitat parameters included in best‐supported GLMMs differed among extents. Variation in Arkansas darter abundance was explained by canopy cover and channel depth at the reach (54% explained) and segment (56%) extents, and stream width and depth at the basin extent (37%). Partial dependence plots from multiple regression GLMMs revealed that Arkansas darter abundance was negatively correlated with increasing channel depth across all extents, increasing canopy cover at reach and segment extents, and increasing channel width at the basin extent. Our results highlight scale‐specific relationships between Arkansas darter abundance and local habitats across multiple spatial extents. These findings provide direction for assessing stream fish ecology pattern‐process relationships at the appropriate spatial scales and benefit native fish conservation by highlighting the application of hierarchy theory to address management challenges.