THE EXPLOITATION OF FOOD RESOURCES BY SOIL MESO-INVERTEBRATES AND MACRO-INVERTEBRATES

A food web is presented for soil meso- and macroinvertebrates in grass land. It is based on field observations made using a large custom - bu ilt rhizotron which allows the soil ecosystem to be studied under natu ral conditions without disturbing the animals or their environment. Th e food web has many characteristics (e.g. number of trophic links, fre quency distribution of food chain lengths, linkage density, connectanc e) in common with webs of similar size from other habitats but there a re also important differences. There are unusually low proportions of trophic links between top and intermediate species and between interme diate species. The proportion of links with basal species is very high . We observed very few taxa specialized for catching and consuming liv e meso- or macroinvertebrates and those present were never abundant. E ven top predators such as geophilomorph centipedes also exploited inan imate basal resources. Interactions between animal taxa may therefore be relatively rare and weak. There was a high degree of omnivory, no c lear compartmentation, and separate herbivore and decomposer food webs could not be distinguished. Plant root systems were an important reso urce for many soil animals. There was evidence that certain taxa fed p referentially on different parts of the root system but there was no c lear evidence for exclusive guilds or species packing.