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Abstract

Community structure may be governed by many abiotic and biotic factors. Of the biotic factors, predation is often considered to be critical in structuring freshwater stream communities. In the Warm Fork of the Spring River, the crayfish Cambarus hubbsi is found mainly in riffles, whereas the crayfish Orconectes marchandi is found in high numbers in pools. We hypothesized that predation, mainly by fish, is a factor causing this segregation. Higher predation rates for C. hubbsi than 0. marchandi in the pools and higher predation rates for 0. marchandi than C. hubbsi in the riffles were expected. A transplant tethering experiment was conducted to test whether predation influences habitat selection. Substrate, water depth, and current velocity were also taken into account. In the pool, predation rates were significantly greater on C. hubbsi than 0. marchandi, but predation rates were equal for the two species in the riffle. This suggests that predation is a factor in keeping C. hubbsi out of pools, but is not a factor in keeping 0. marchandi out of riffles. Also, significantly greater predation rates overall were found in the pool than in the riffle. The pool was significantly deeper and had lower substrate diversity than the riffle. These findings suggest that predators are important in affecting crayfish habitat use; differential predation rates occur between habitats and greater predation rates occur in pools than in riffles.

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