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More Discoveries with Fewer Deaths: Substituting Dragonfly Exuviae for Living Insects in Stable Isotope Studies of Food Webs
Gaines, Karen H.
Gaines, Karen H.
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Abstract
The stable carbon and nitrogen isotopic signatures (13C, 15N) of consumers’ tissues are used to infer their trophic roles in communities, but stable isotope analysis often requires the undesirable sacrifice of small-bodied animals. My objectives were to determine if the differences between 13C and 15N of whole dragonflies and their nonliving exuviae (final-instar larval exoskeletons) are similar enough to enable their substitution, and to characterize spatial, taxonomic, and temporal variability in 13C, 15N, and adult-exuviae isotopic fractionation (Δ13C, Δ15N). In New Mexico, I compared two coexisting species of emerging adults and their exuviae, conspecifics emerging from two different sinkholes, conspecifics from the same sinkhole on different dates, and conspecific larvae. In Kansas, I compared four species of adult-exuviae pairs and the exuviae of three additional species present in various combinations at a constructed pond, a reservoir, and a small artificial pond complex. There were spatial and taxonomic differences in mean 13C and 15N and the direction of Δ13C, but all mean absolute Δ13C and Δ15N values were less than 3.3‰ and 1.5‰ respectively, regardless of state, waterbody, taxon, or collection date. Furthermore, mean 13C and 15N of two species of larvae were intermediate between the signatures of conspecific adults and exuviae. This study demonstrates that exuviae can be used instead of entire dragonflies in stable isotope studies of food web structure because the 13C and 15N of exuviae very closely correspond to adult and larval signatures. This correspondence will enable trophic research to proceed in a manner that reduces negative impacts on sensitive dragonfly populations and their fragile aquatic habitats.
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Date
2022-08-31
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University of Kansas
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Keywords
Ecology, Conservation biology, Entomology, Conservation ecology, Dragonflies, Exuviae, Food webs, Odonata, Stable isotopes