Competition and cocoon consumption by the earthworm Aporrectodea longa

Abstract

We investigated interactions between the deep burrowing earthworm Aporrectodea longa and three other common pasture species ( A. caliginosa, A. trapezoides and Microscolex dubius) and the roles these other species would have on reducing the ability of A. longa to colonise agricultural land in the high rainfall zone (>600 mm) of southern Australia. Experiments were conducted in pots in the laboratory or glasshouse and in cages in the field. In most experiments, field soil was used and in some experiments, an artificial soil of commercially available garden loam mixed with bentonite clay was used. To determine whether competition occurred, the growth, survival and reproduction of earthworms was compared between single-species and mixed-species treatments. Competition between A. longa and A. caliginosa was weak and no competitive effects were measured between A. longa and A. trapezoides. The presence of A. longa significantly reduced the reproductive output of M. dubius, possibly by removing its food source and habitat or consuming its cocoons. This is the first reported evidence that individuals of one earthworm species may consume the cocoons of another. The establishment of A. longa into pastures in southern Australia is unlikely to be impeded by the presence of earthworm species already established. The spread of A. longa in this region will not significantly reduce populations of A. trapezoides and A. caliginosa, but is likely to decrease populations of M. dubius significantly.