Interspecific interactions between earthworms: A laboratory-based investigation

Three laboratory-based experiments were undertaken to assess interspecific interactions using a range of earthworm species. These were seen as prelimi nary steps towards the production of mixed species populations for inoculat ion at land restoration sites. In the first experiment, hatchlings of 2 ane cique species (Aporrectodea longa and Lumbricus terrestris) and 2 endogeic species (Allolobophora chlorotica and Aporrectodea caliginosa) were culture d in paired and single species treatments under optimal conditions for grow th and survival. Growth rates of all four species were negatively affected by the presence of other species. It is proposed that the extent to which g rowth rates were influenced was determined by the degree of niche overlap b etween paired species (e.g. L. terrestris growth rates were most negatively affected by A. longa). Experiments relating to levels of soil compaction (Experiment 2) and positi on of feed within the soil profile (Experiment 3) employed A. chlorotica, L . rubellus and L. terrestris (endogeic, epigeic and anecique species, respe ctively). In experiment 2 cocoon production was determined for the 3 specie s in all combinations within compacted (1.52 g cm(-3))or uncompacted (1.37 g cm(-3)) soil treatments. Soil compaction significantly (p < 0.01) reduced L. terrestris cocoon production in monoculture, whilst reproductive output by L. rubellus was not significantly affected by compaction. Cocoon produc tion In paired culture was not significantly affected, in both compacted an d uncompacted treatments, except in the pairing of L. rubellus and L. terre stris. In this pairing L. rubellus cocoon production was significantly (p < 0.01) reduced at both soil bulk density treatments compared with the monoc ulture of this species. This resulted from interspecific competition for or ganic matter at the soil surface. In experiment 3 the effect of feed positi on within the soil on cocoon production was determined for various species combinations. Reproductive output was again negatively influenced hy the pr esence of other species. The effect of feed position was species specific d epending on innate feeding behaviour (e.g. A. chlorotica produced the great est number of cocoons in cultures where the feed was mixed into the soil).