Great Basin Naturalist


Laboratory experiments were undertaken to assess the effects of three levels of cobble embeddedness on the microdistribution of the sculpin Cottus beldingi and its stonefly prey, Skwala Americana. Experiments were conducted separately and together as predator and prey in temperature- and flow-controlled artificial streams. When tested either separately or together, both the predator sculpin and its stonefly prey occurred in significantly greater numbers on substrata having unembedded cobbles than substrata having half- or completely embedded cobbles. Stonefly densities were greater in substrata having unembedded cobbles even though predator densities within the more embedded cobble patches were significantly lower. These findings support the hypothesis that higher predator densities influence prey densities less than the structural habitat quality of unembedded-cobble patches.