Trophic Structure and Feeding Rates of Forest Soil Invertebrate Populations

Abstract

Trophic level relationships of a soil invertebrate community were determined using the transient behavior of cesium-137 in experimental soil microcosms. Feeding rates were estimated from radionuclide mass balance equations using radiocesium uptake coefficients, equilibrium concentrations of 137Cs in consumers, and 137Cs composition of food bases. The fungivore trophic level included Scatopsidae larvae (Diptera), Enchytraeidae (Annelida), Entomobryidae and Onychiuridae (Collembola), Rhodacaridae (Mesostigmata), and Oribatulidae, Camasiidae, Carabodidae, and Cymbaeremaeidae (Oribatei). Approximately 60 per cent of the total faunal biomass occurred in the fungivore trophic level. Fungivores averaged 7.0 ? 2.4 per cent dry body weight ingested per day. Cecidomyiidae larvae (Diptera), Diplopoda, Isotomidae (Collembola), Uropodina, and Phthiracaridae (Oribatei) were determined to be surface-feeding saprophages. Subsurface-feeding saprophages included Symphyla, Cillibidae (Uropodina), and Palaeacaridae and Epilohmannidae (Oribatei). Surfacefeeding saprophages averaged 1.0 ? 0.4 per cent dry body weight ingested per day. Feeding rates were not calculated for saprophages feeding within the mineral soil horizon. Predators included Dolichopodidae larvae (Diptera), gamasine mites, and the Scutacaridae and other prostigmatid mites. Predators averaged 2.5 ? 1.0 per cent dry body weight ingested per day.