Are Riffles Keystone Habitats in a Low-Gradient Prairie Stream?; Implications for Riverscape Ecology and Stream Conservation

A riverscape approach to stream ecology and conservation focuses on how stream habitats are integrated to create sustainable mosaics that support diverse biotic communities. Here, we (1) test if stream habitat units are categorical or continuous, (2) quantify the distribution of these units across a riverscape, (3) evaluate fish species-habitat relationships, then (4) identify repositories of native stream fish biodiversity. We sampled the Neosho and Cottonwood Rivers, Kansas from May-October 2013.  Habitats were categorized based on physical characteristics (depth, flow velocity, substrate size).  Habitat specific fish samples were collected using mini-Missouri trawls. Within habitat groups, riffles and pools varied widely by velocity and depth (e.g., fast and slow riffles, deep and shallow pools). A select group of species were riffle or pool specialists.  Riffles were the limiting habitat in our study system, comprising < 5% of the total proportion of habitat sampled.  However, fish abundance was significantly higher in riffles (p < 0.001) relative to other habitats and species richness was highly correlated with riffle patch density (R² = 0.639; p = 0.005). Protecting habitats which have dispropotionately large effects on biodiversity relative to habitat size and abundance, here termed keystone habitat, can be used for stream conservation efforts.