a1 Research Core for Interdisciplinary Sciences, Okayama University, 3-1-1, Tsushimanaka, Okayama, 700-8530, Japan
a2 Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-Nihonmatsu, Sakyo-ku, Kyoto 606-8501, Japan
a3 Department of Biological Environmental Sciences, Yamaguchi University, 1677-1, Yoshida, Yamaguchi, 735-5838, Japan
a4 Faculty of Agriculture, Ehime University, 3-5-7. Tarumi, Matsuyama 790-8566, Japan
a5 Center for Ecological Research, Kyoto University, 2-509-3, Hirano, Otsu, Shiga, 520-2113, Japan
a6 Graduate School of Agricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
Carbon and nitrogen stable isotope ratios (δ13C and δ15N) have been used to study the structure of food webs. However, few studies have examined how a terrestrial food web can be depicted by this technique. We measured δ13C and δ15N in various consumers of four trophic groups (detritivores, herbivores, omnivores and predators), including vertebrates and invertebrates (14 orders, ≥24 families), as well as canopy and understorey leaves in a tropical rain forest in Malaysia. We found that δ13C and δ15N of the consumers differed significantly among the trophic groups. The predators had significantly higher δ13C than the herbivores, and were similar in δ13C to the detritivores, suggesting that most predators examined depend largely on below-ground food webs. δ15N was higher in predators than detritivores by about 3‰. The comparison of δ13C in plant materials and herbivores suggests that most herbivores are dependent on C fixed in the canopy layers. The vertebrates had significantly higher δ15N and δ13C than the invertebrates of the same trophic group, likely reflecting differences in the physiological processes and/or feeding habits. This study indicates that stable isotope techniques can help better understanding of the terrestrial food webs in terms of both trophic level and the linkage of above- and below-ground systems.
(Accepted October 05 2009)