This paper reviews the abundance and species richness, and factors that cause these parameters to vary, of mesofauna and macrofauna in an upland grassland soil studied intensively under the NERC Soil Biodiversity Programme. The concept that competitive exclusion does not act within soil communities is reviewed in light of these findings, which are placed in the context of the wider literature relating to earthworm, enchytraeid, collembolan and mite diversity, and factors that influence these, with particular reference to land management. The second half of the paper reviews laboratory and field 13C-tracer studies, carried out under the programme, that assess linkages between specific biota and ecosystem processes. The concept of functional redundancy in soil food webs is discussed in the context of these studies. We conclude that competitive interactions occur most widely amongst soil macrofauna, and that competitive exclusion amongst mesofauna is potentially limited by both fine-scale spatial heterogeneity and predation. The most profound impacts of soil fauna on soil properties at Sourhope appeared to be due to the presence of macrofauna in soil communities. There was also evidence for functional redundancy at the species level amongst soil biota, but this was dependent upon which ecosystem process was measured. We conclude that it is likely that functional redundancy at the species level occurs most widely in species rich faunal groups with generalist feeding behaviour. © 2006 Elsevier B.V. All rights reserved.