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

Abstract 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 (δ 13 C and δ 15 N) of the invertebrates collected at Arahama ranged from 0.3 to 6.3‰ for δ 15 N and from −27.3 to −23.3‰ for δ 13 C. At Gamo, invertebrates δ 13 C values ranged from −26.1 to −23.5‰ and δ 15 N 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 δ 13 C values. The less enriched group (δ 13 C  13 C > −25‰). The range of δ 15 N for the present animals exceeded two trophic levels. While, the gradual 15 N enrichment within the invertebrates species may indicate the dominance of omnivory in soil food webs. The differences between sites in δ 15 N confirm the importance of studying the trophic structure of soil fauna locally.