Hierarchy Theory Reveals Multiscale Threats to Arkansas Darter (Etheostoma cragini) in Modified Great Plains Riverscapes

Hierarchy theory in landscape ecology states that ecosystem processes are organized into discrete spatiotemporal scales and interact across these scales to structure the distribution and abundance of organisms. Arkansas Darter (Etheostoma cragini) is an endemic Great Plains fish and a candidate species for protection under the Endangered Species Act because of landscape changes occurring in the Great Plains. We applied hierarchy theory to test for processes affecting Arkansas Darter density along environmental gradients in Kansas streams using principal components analysis and quantile regression at discrete spatial scales, including watersheds (10⁵ m), segments (10⁴ m), reaches (10³ m), and links (10² m). Results indicate ecosystem processes indeed interact across scales to regulate Arkansas Darter density, including groundwater dynamics across watersheds, precipitation and flooding regimes along segments, hydrodynamic habitat creation and flow connectivity throughout reaches, and local habitat fluxes within links. The natural hierarchy of ecosystem processes affecting distribution and abundance of Arkansas Darter is superimposed by a second hierarchy of anthropogenic landscape changes in the Great Plains that effectively fragment scale transition by ecosystem processes. Our study reiterates the notion that conservation of stream fishes such as the Arkansas Darter should be addressed through maintenance of interactive processes at multiple scales.