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Presented at the NABS Annual meeting, Athens, Georgia, 2003
in Community Ecology II
Size structure influences the functional roles of crayfish (Orconectes propinquus) in a stream community (Shivering Sands Creek,Wisconsin).
J.D. Hoekstra and D.A. Soluk. Department of Animal Biology, University of Illinois, Urbana, IL 61801
Crayfish diet and behavior vary with body size. Therefore size structure may influence the functional roles of crayfish populations. We evaluated this hypothesis with a month-long summertime in situ experiment. Crayfish size structure was manipulated within 0.25 m2 cages. Treatments were exclosure (no crayfish); artificial bioturbation (no crayfish, substrates manually disturbed to mimic crayfish bioturbation); juvenile-only (18 juveniles); adult-only (2 large males); and mixed (9 juveniles, 1 adult male). Colonizable substrates and leaf packs were used to assess treatment effects on invertebrate communities and leaf breakdown rates. We also measured survival of large limnephilid larvae stocked into cages. Treatments influenced the abundance of macroinvertebrates on tiles (P < 0.001) but not in rock baskets (P > 0.2). Abundance was highest on bioturbation tiles and was significantly reduced for juvenile-only and mixed treatments. Specific taxa showed complex, variable responses to treatments. The survival of limnephilids was strongly reduced in the presence of adult crayfish (treatment P = 0.002). For both sugar maple and American beech litter, breakdown was fastest in the presence of juveniles (treatment P < 0.001). In summary, juvenile crayfish can be functionally important in streams and their roles may differ qualitatively from those of adults.
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