Trophic structure of a macroarthropod litter food web in managed coniferous forest stands: a stable isotope analysis with delta N-15 and delta C-13

We studied the composition of a litter detrital. community in a temperate coniferous forest using stable isotopes of nitrogen and carbon. Samples of mineral soil, bulk Litter material, macroarthropods and understory plants were collected from ten experimental. forest stands. Half of the stands were previously thinned 17-42 years ago, the other half served as controls. Values of delta(15)N and delta(13)C were based on the analysis of almost 500 individuals of at Least 22 species in 11 arthropod families. The isotopic analysis showed a significant increase in delta(15)N and delta(13)C values with soil depth. Isotopic signatures of macroarthropods ranged from -26.51 parts per thousand to -20.52 parts per thousand for delta(13)C and -2.85 parts per thousand to 5.10 parts per thousand for parts per thousand(15)N. All consumers showed levels of delta(13)C enrichment substantially higher than those of primary producers and Litter. Predators were generally significantly more N-15 enriched than detritivores and herbivores, but their delta(13)C levels were similar to those of primary consumers. Our data indicate that this community consists of at least 2-3 trophic levels with a considerable amount of variation in the N-15 enrichment among detritivores and predators. We suggest that the spread of delta(15)N values of predators likely reflects the diversity of potential. prey among detritivores and a varying degree of intraguild predation among different species. Our findings generally agree closely with the results of similar studies from other forest litter communities. Thinning did not appear to influence the overall, isotopic composition of the detrital. food web. Extensive omnivory and intraguild predation among Litter consumers may buffer long-term effects of thinning on the trophic structure of these species-rich communities. (c) 2004 Elsevier GmbH. All rights reserved.