SOIL AND LITTER MICROARTHROPOD POPULATIONS FROM 2 CONTRASTING ECOSYSTEMS IN SEMIARID EASTERN AUSTRALIA

In a project designed to identify and quantify acarine communities in semiarid eastern Australia, microarthropod populations in surface soil and litter were sampled during different seasons across a range of mi crohabitats in both heavy- and medium-textured soils. Major difference s in mite assemblages were recorded between these soils, as well as be tween contrasting microhabitats within each soil type. In the medium-t extured soil, richness and abundance of Acari taxa were related to soi l organic carbon in the surface soil (0-1 cm), particularly for the Pr ostigmata. This relationship was not apparent in the heavy-textured so il where organic carbon content was considerably higher (4-9.5% cf. 0. 4-1.75%). The highest densities on the medium-textured soil (c. 2600 m (-2) dominated by Speleorchestes, Eupodes and Pseudocheylus spp.) were recorded in mulga groves where there was abundant surface litter. How ever these densities were greatly exceeded under annual grassland on t he heavy-textured soil (c. 14,000 m(-2), dominated by Afrotydeus spp.) . These are amongst the highest mite densities recorded on semi-arid s oils in Australia, possibly due to these grasslands being the least sa line of the sites sampled in the chenopod shrublands. Broad similariti es in microarthropod composition at family and generic levels in simil ar ecosystems in Australia and North America suggest either convergent evolution under similar selection pressures or long distance dispersa l in the past. Inter-hemisphere dispersal of these microscopic animals may have been facilitated by stronger winds which prevailed during gl acial periods, despite the inter-tropical convergence zone over the Pa cific Ocean. (C) 1996 Academic Press Limited