Trophic structure of macro- and meso-invertebrates in Japanese coniferous forest: Carbon and nitrogen stable isotopes analyses

Few studies have been published on the feeding ecology of Japanese soil fauna based on stable isotope analysis. Therefore, the present work aims to use this technique for studying the trophic structure of Japanese soil fauna at two coniferous forests. Significant differences were observed between investigated sites (Arahama and Gamo) in genus richness and abundance, while for Shannon diversity indexes the difference was non-significant. The isotopic signatures (δ13C and δ15N) of the invertebrates collected at Arahama ranged from 0.3 to 6.3‰ for δ15N and from −27.3 to −23.3‰ for δ13C. At Gamo, invertebrates δ13C values ranged from −26.1 to −23.5‰ and δ15N values ranged from 1.6 to 6.8‰. At both sites, invertebrates formed two distinct groups on the basis of combined C and N stable isotope ratios. The locations of these groups related to δ13C values. The less enriched group (δ13C < −25‰) and the more enriched one (δ13C > −25‰). The range of δ15N for the present animals exceeded two trophic levels. While, the gradual 15N enrichment within the invertebrates species may indicate the dominance of omnivory in soil food webs. The differences between sites in δ15N confirm the importance of studying the trophic structure of soil fauna locally.