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Stable C and N isotope ratios reveal soil food web structure and identify the nematode Eudorylaimus antarcticus as an omnivore–predator in Taylor Valley, Antarctica

Abstract

Soil food webs of the McMurdo Dry Valleys, Antarctica are simple. These include primary trophic levels of mosses, algae, cyanobacteria, bacteria, archaea, and fungi, and their protozoan and metazoan consumers (including relatively few species of nematodes, tardigrades, rotifers, and microarthropods). These biota are patchily distributed across the landscape, with greatest faunal biodiversity associated with wet soil. Understanding trophic structure is critical to studies of biotic interactions and distribution; yet, McMurdo Dry Valley soil food web structure has been inferred from limited laboratory culturing and microscopic observations. To address this, we measured stable isotope natural abundance ratios of C (13C/12C) and N (15N/14N) for different metazoan taxa (using whole body biomass) to determine soil food web structure in Taylor Valley, Antarctica. Nitrogen isotopes were most useful in differentiating trophic levels because they fractionated predictably at higher trophic levels. Using 15N/14N, we found that three trophic levels were present in wet soil habitats. While cyanobacterial mats were the primary trophic level, the nematode Plectus murrayi, tardigrade Acutuncus antarcticus, and rotifers composed a secondary trophic level of grazers. Eudorylaimus antarcticus had a 15N/14N ratio that was 2–4‰ higher than that of grazers, indicating that this species is the sole member of a tertiary trophic level. Understanding the trophic positions of soil fauna is critical to predictions of current and future species interactions and their distributions for the McMurdo Dry Valleys, Antarctica.

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Acknowledgements

This work was funded by the United States National Science Foundation (NSF), McMurdo Dry Valleys Long Term Ecological Research (MCM LTER) site, PLR 1115245. Geospatial support for this work was provided by the Polar Geospatial Center under NSF OPP awards 1043681 & 1559691. We are grateful to many people who helped with this work, especially the McMurdo Dry Valleys LTER group. Matthew Knox helped collect samples in the field. Members of the Wall Lab at Colorado State University, in particular Amber Cavin, Cecilia Milano de Tomasel, and Emily Bernier, helped with lab work. Thanks also to the Crary Laboratory staff, Stable Isotope Mass Spectrometry Laboratory at Kansas State University, and PHI helicopters whose assistance with lab and fieldwork helped make this work possible.

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Correspondence to E. Ashley Shaw.

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Shaw, E.A., Adams, B.J., Barrett, J.E. et al. Stable C and N isotope ratios reveal soil food web structure and identify the nematode Eudorylaimus antarcticus as an omnivore–predator in Taylor Valley, Antarctica. Polar Biol 41, 1013–1018 (2018) doi:10.1007/s00300-017-2243-8

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Keywords

  • Dry Valleys
  • Predator
  • Trophic levels
  • Isotopic fractionation
  • Feeding ecology
  • Connectivity