Spatially nested models of habitat use by the Niangua darter, Etheostoma nianguae, a threatened Ozark stream fish

The Niangua darter, Etheostoma nianguae, is a small, benthic stream fish endemic to the Osage River basin in south-central Missouri. It is a member of the perch family, Percidae, and is distinguished from all other darters by its unique body shape and markings. Only eight of ten known populations remain extant. The darter was listed as threatened under the U.S. Endangered Species Act in 1985 due to its limited distribution and small population sizes, fragmentation of its range by dam construction, and general stream habitat degradation.; I studied the darter's habitat use on three spatial scales of decreasing size: stream, reach, and microhabitat. At each of these scales, habitat variables were identified that were significantly associated with darter presence-absence. Logistic regression models were developed to predict the probability of darter presence at all three scales, using one or more habitat variables as predictors. The microscale model was validated with additional sampling in new localities.; Different factors emerged as significant on different scales. Stream size and measures of confluence difference (CD) were important stream-scale variables. The CD metric was proposed to be a zoogeographic barrier to Niangua darter presence. Riffle spacing, gradient, bank erosion, and streambed elevation were important at the reach scale, and water depth and substrate mean particle size were important microhabitat variables. The microscale model successfully predicted Niangua darter presence in other streams.; These hierarchically nested habitat models can be used along with a previously developed faunal index to rank sites in the Osage River basin based on their relative suitability for Niangua darter presence.