Soil animals and ecosystem processes: How much does nutrient cycling explain?

SummaryTrophic-dynamic hypotheses have been extensively tested by manipulating the presence of soil animals in experimental laboratory microcosms. Soil animals typically have pronounced effects on microbial populations, nutrient cycling and plant growth. However, because often only the total effect has been reported, the relative importance of feeding interactions versus non-trophic effects remains obscure. Using simple calculations based on mass conservation I argue that the observed faunal effect on microbes and system functioning is often larger than can be explained by trophic dynamics and nutrient cycling. Non-trophic effects may help to explain why microcosm experiments have failed to support trophic-dynamic predictions like trophic cascades. Since such effects are also likely independent of species identity and population density, they may facilitate the interpretation of experiments where decomposition processes have been found to be largely insensitive to soil fauna diversity.