Habitat shift of a native darter Etheostoma olmstedi (Teleostei: Percidae) in sympatry with a non-native darter Etheostoma zonale

Etheostoma zonale, the banded darter, was introduced to the Susquehanna River basin of Pennsylvania through an interbasin transfer, or transplantation of native fishes outside their natural range. We examined the habitat use of a darter native to the Susquehanna River drainage E. olmstedi, the tessellated darter, in sympatry and allopatry with E. zonale to determine if its habitat use was different. In the presence of E. zonale, E. olmstedi occupied significantly (P < 0.05) shallower habitats (mean depth < 27 cm) with smaller substrates (mean substrate index < 32) and slower water velocities (mean water velocity < 0.13 m s^-1) than in sites without E. zonale. The habitat shift of E. olmstedi was, accompanied by a compression of niche breadth. The results are consistent with the hypothesis that E. zonale excludes E. olmstedi from riffle and run habitats, restricting E. olmstedi to shallow pools and stream margins.