Arthropod trophic relationships in a temperate rice ecosystem:: A stable isotope analysis with δ13C and δ15N

Arthropod trophic relationships intemperate rice fields during the growing season were explored in 2000 and 2001 by measuring signatures of naturally occurring carbon and nitrogen stable isotopes. delta C-13 and delta N-15 values for rice plants, soil, and arthropods varied slightly between both years, and the values were rather distinctive according to functional groups. Isotopic changes in rice plants affected values for herbivorous insects. Seasonal changes in delta C-13 and delta N-15 values for predators indicated that prey composition of their diets changed seasonally. Early in the season, there were two distinct clusters: (1) rice plants-herbivorous insects-parasitoids cluster and (2) filter-feeders/detrivores and predators cluster. The correlations in each case suggest interactions. During mid-season, the rice plants-herbivorous insects-parasitoids interaction was maintained, and herbivorous insects such as planthoppers were linked to predators. Also, detritivores such as Entomobryidae spp. seemed to be linked. During the late season, close interactions occurred at all trophic levels. Our study provided isotopic evidence that filter feeders/detrivores such as Chironomidae and Entomobryidae play a valuable role in maintaining the predator complex in the rice ecosystems during the rice-growing season. Also, fundamental data of stable carbon and nitrogen isotopes acquired in this study would be of value for use in advanced community studies for rice fields.