Distribution of Heteromurus nitidus (Hexapoda, Collembola) according to soil acidity: interactions with earthworms and predator pressure

Culture (8 weeks, in sieved fresh humus) and choice (16 weeks in compartmen ted boxes containing fresh or defaunated humus, or 5 days on compacted humu s) experiments at varying pH values demonstrated that the soil-dwelling Col lembolan Heteromurus nitidus (Entomobryomorpha) can live and even prefer hu mus with pH < 5.0, contrary to results of field studies. Choice experiments on moder (pH 7.8) and calcic mull (pH 3.9) showed that H. nitidus was sign ificantly attracted by the earthworms Allolobophora chlorotica and Aporrect odea giardi whatever the humus form, except when moder was present on both sides. This attraction by earthworms may partly explain the field distribut ion of H. nitidus. A strong predator pressure was detected in some of the r eplicates, which seemed to have an effect on densities and distribution of H. nitidus, as well. Causes of the attraction by earthworms (food resources , pore size, moisture) are discussed. A trophic cause is particularly suspe cted. (C) 1999 Elsevier Science Ltd. All rights reserved.