PARENT SESSION
Poster Session #28: Animal Ecology.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
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Variation in trophic shift for stable isotope ratios of carbon, sulfur, and nitrogen.
MCCUTCHAN, JAMES1.2, LEWIS, WILLIAM2, KENDALL, CAROL3, 2 3
ABSTRACT- Use of stable isotope ratios to trace pathways of organic matter through consumer food chains requires knowledge of the isotopic shift between diet and consumer. Variation in trophic shift among consumers can be substantial, but the causes and effects of such variation have received little attention. In this study, 6 consumer species were raised under controlled conditions. For each species, the isotopic shift between diet and consumer was measured for carbon (C), sulfur (S), and nitrogen (N). For the new data and the published literature, the mean isotopic shift for C was +0.5±0.13‰, but the shift for C was higher for consumers analyzed as muscle (+1.1±0.27‰) than for consumers analyzed whole (+0.4±0.15‰). Among consumers analyzed whole, the trophic shift for C was lower for consumers acidified prior to analysis (-0.2±0.21‰) than for unacidified samples (+0.6±0.18‰). For N, trophic shift differed between consumers raised on high-protein (+2.6±0.28‰) and low-protein diets (+1.6±0.29‰). The trophic shift for S also differed between high-protein (+2.0±0.65‰) and low-protein diets (-0.5±0.56‰). Thus, methods of analysis and dietary differences can affect trophic shift for consumers. Such variation is important because small errors in estimates of trophic shift can result in large errors in estimates of the contribution of sources to consumers or in estimates of trophic position.
KEY WORDS: stable isotope ratios, trophic shift, fractionation, diet