The structure of a food web in a tropical rain forest in Malaysia based on carbon and nitrogen stable isotope ratios

Abstract

Abstract: Carbon and nitrogen stable isotope ratios (δ 13 C and δ 15 N) 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 δ 13 C and δ 15 N 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 δ 13 C and δ 15 N of the consumers differed significantly among the trophic groups. The predators had significantly higher δ 13 C than the herbivores, and were similar in δ 13 C to the detritivores, suggesting that most predators examined depend largely on below-ground food webs. δ 15 N was higher in predators than detritivores by about 3‰. The comparison of δ 13 C in plant materials and herbivores suggests that most herbivores are dependent on C fixed in the canopy layers. The vertebrates had significantly higher δ 15 N and δ 13 C 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.