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Presented at the NABS Annual meeting, Athens, Georgia, 2003
in Population Ecology
Caddisfly case building under differing predation and drying regimes
S.E. Mattie1,2, S.A. Wissinger1,2, and J.E. Jannot2,3. 1Environmental Science Department, Allegheny College, Meadville, PA 16335 USA, 2Rocky Mountain Biological Laboratory, Crested Butte, CO 81224 USA, 3Department of Biological Sciences, Purdue University, West Lafayette, IN 47907 USA
Larval caddisflies potentially face tradeoffs related to the allocation of energy to case building vs. growth and development depending on the relative importance of predation and time constraints related to wetland drying. We reared de-cased Limnephilus externus caddisflies under different predation threats (salamanders present, absent) and drying regimes (level maintained vs. slowly dehydrating) in laboratory microcosms, and measured case size, body mass, and instar development. We found that caddisfly body mass was greater in permanent than temporary treatments, regardless of salamander presence. Case mass did not differ among treatments; therefore, the body mass / case mass ratio was significantly greater in permanent than temporary microcosms. Residual analysis based on regression of case mass on body mass revealed that observed case masses in the permanent treatments were significantly heavier (for a given body mass) than predicted, regardless of the presence of salamanders. Observed case masses were the same or lighter than predicted in temporary treatments. Our results suggest allocation of energy to case building (vs. growth and development) in this species is primarily affected by time constraints and not predator threat. This is consistent with previous studies in which larval behaviors, and not case morphologies determined vulnerability to predation.
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