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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Life Histories
TROPHIC AND HABITAT RELATIONSHIPS OF CLAASSENIA SABULOSA IN THE UPPER COLORADO RIVER.
R.A. Thorp, J.B. Monroe, T.A. Wellnitz, and N.L. Poff. Department of Biology, Colorado State University, Fort Collins, CO, USA, 80523
To investigate the distribution and feeding habits of the predatory stonefly nymph Claassenia sabulosa, a streambed survey was conducted over a 3 d period in the upper Colorado River during August 2001. C. sabulosa were sampled from 45 1 × 1 m sample plots that were characterized according to several habitat components (current velocity, depth, insect retreat abundance). These plots were located along 8 line transects located in both runs and riffles. Individual C. sabulosa head capsules were measured to determine developmental stage, and prey preference was determined through examination of gut contents. More than any other habitat variable, the abundance of retreats of the chironomid, Pagastia partica correlated positively with C. sabulosa densities. Gut analysis revealed P. partica was the most common prey among early C. sabulosa instars, making up more than half of all prey consumed. As C. sabulosa grew larger, its diet shifted to primarily baetids and simuliids. These data indicate C. sabulosa is a specialist predator that shows clear ontogenetic prey shifts, and they further suggest C. sabulosa can track the abundance of certain sessile prey species.
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