Great Basin Naturalist


Microhabitat selection by the johnny darter (Etheostoma nigrum) was examined in the North Laramie River, Platte County, Wyoming, where it does not occur with other darter species in the same stream reach. Electivity indices based on microhabitat observations indicate that E. nigrum avoids riffles and selects certain microhabitats characterized by intermediate water depths in pools and slow-moving runs with a substrate composed primarily of silt and sand. Niche breadth and electivity values for total depth, bottom water velocity, and substrate measurements from this study indicate that E. nigrum is a habitat generalist, except at the extreme ends of the habitat gradient. Habitat use here is generally similar to other studies where E. nigrum occurred with one or more other darter species. This study found little evidence for competitive release in the absence of other darters.