Dual stable isotope analysis (delta C-13 and delta N-15) of soil invertebrates and their food sources

More research is required to validate and refine natural abundance stable isotope ratio techniques as a tool. for the investigation of the feeding ecology of soil animals and trophic relations in soil food webs. Isotope ratios of C (delta(13)C) and N (delta(15)N) were measured in herbivorous and detritivorous invertebrate groups, namely lumbricid earthworms (7 species), enchytraeid worms (3 species), slugs Q taxa), and their potential food sources in an arable system. Intrapopulation delta(15)N variation in the slug Deroceras reticulatum (n = 52) was large (range 4.2%.), possibly reflecting spatial variability in the food sources. Significant correlations between C:N ratios and isotope ratios in earthworms suggest that factors other than feeding may influence isotopic patterns. One enchytraeid species, Enchytraeus buchholzi, was enriched in C-13 and strongly depleted in N-15 compared to all other groups. Invertebrates formed a continuum when considered in relation to C and N separately, but fell. into two distinct groups on the basis of combined C and N isotope ratios. The less enriched group represents herbivorous and titter-feeding species, while the more enriched group represents soil feeders. It is concluded that delta(13)C measurements could provide a means of assigning separate baseline delta(15)N values to primary and secondary decomposers, which in turn could improve the inference of higher trophic levels, omnivory and intraguild predation. (C) 2004 Elsevier GmbH. All rights reserved.