Stable isotopes and terrestrial herbivorous insects: a field based study of interspecific 15N and 13C variation.
Spence, Kenneth*,1, Rosenheim, Jay1, 1 University of California, Davis
ABSTRACT- Researchers will be able to use stable isotope analysis to study community structure in an efficient manner without the necessity of calibrations if isotopic enrichment values are consistent, or if variation in enrichment values can be explained. In this study, we generated an experimental data set of 15N and 13C enrichment means for 22 terrestrial herbivorous arthropods feeding on 18 different host plants. The species enrichment means ranged from −3.47‰ to 1.89‰ for 13C and −0.20‰ to 6.59‰ for 15N. Overall mean enrichment values for the experimental data set were −0.53 ± 0.26‰ for 13C and 1.88 ± 0.37‰ for 15N. Comparing the overall enrichment means to those from previous studies, we found 13C enrichment was significantly lower. Though also lower, mean 15N enrichment did not differ significantly from similar means reported in recent meta-analyses. The experimental data set provided no support for recent hypotheses proposed to explain variation in enrichment values, including the proposed roles for consumer feeding mode, development type, and diet C:N ratio. Our results indicate that species enrichment values are variable even in this relatively narrowly defined group of organisms and that our ability to predict herbivore enrichment values based on physiological, ecological, or taxonomic traits is low. The primary implications are that 1) mean enrichment will have to be calculated for each trophic link of interest, rather than relying on estimates from a broad survey of animal taxa and 2) the special advantage of using stable isotope analysis to probe animal communities that are recalcitrant to other modes of study will be somewhat diminished as a consequence.
Key words: trophic position, community ecology, enrichment, arthropod
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