02332nas a2200193   4500008004100000245017900041210006900220260001200289300001600301490000700317520164300324100001701967700001701984700002202001700001702023700002302040700002002063856005502083       2018                        eng d00aStable C and N isotope ratios reveal soil food web structure and identify the nematode <I>Eudorylaimus antarcticus</I> as an omnivore–predator in Taylor Valley, Antarctica0 aStable C and N isotope ratios reveal soil food web structure and  c05/2018  a1013–10180 v413 a<p>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 micro- scopic observations. To address this, we measured stable isotope natural abundance ratios of C (13C/12C) and N (15N/14N) for di erent metazoan taxa (using whole body biomass) to determine soil food web structure in Taylor Valley, Antarctica. Nitrogen isotopes were most useful in di erentiating 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&ndash;4&permil; 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.</p>1 aShaw, Ashley1 aAdams, Byron1 aBarrett, John, E.1 aLyons, Berry1 aVirginia, Ross, A.1 aWall, Diana, H.  uhttp://link.springer.com/10.1007/s00300-017-2243-8