MICROCOSM INVESTIGATIONS INTO THE INFLUENCE OF SHEEP MANURE ON THE BEHAVIOR OF THE GEOPHAGOUS EARTHWORMS APORRECTODEA TRAPEZOIDES AND MICROSCOLEX DUBIUS

A series of experiments was conducted over 96 h in 240-mm-deep soil mi crocosms, to assess the effect of the presence and distribution of she ep manure over the soil surface on the vertical and horizontal distrib ution of burrows and numbers of the earthworms Aporrectodea trapezoide s and Microscolex dubius. Within some microcosms the dung was placed o n half of the soil surface and this caused aggregation, with over two- thirds of the earthworms being found in the soil directly under the ma nure. The presence of surface-applied sheep manure caused both species to aggregate in the surface soil. In contrast, without manure, A. tra peziodes was evenly distributed throughout the soil profile while M. d ubius aggregated in the deeper soil. The pattern of burrow constructio n was also influenced by the presence of surface manure. In the absenc e of manure, burrows of both species were evenly distributed through t he soil, but in the presence of surface manure M. dubius constructed p roportionally more burrows close to the surface. Both species construc ted approximately twice the burrow area in the absence than in the pre sence of surface manure. For both species the daily rate of burrow con struction decreased over the experimental period. From these data we i nferred that there was more widespread and active foraging behaviour i n both species when organic food material was scarce. M. dubius differ ed from A. trapezoides in that it more strongly concentrated foraging activity in the vicinity of the manure food source.