Contribution of oribatid and mesostigmatid soil mites in ecologically based estimates of global species richness

Erwin's method for estimating total global species richness assumes some ho st-specificity among the canopy arthropods. This study examined possible ho st habitat specialization in two major groups of soil arthropods, the oriba tid and mesostigmatid mites, by sampling beneath three tree species: Eucaly ptus pilularis Smith, Eucalyptus propinqua Deane and Maiden and Allocasuari na torulosa (Aiton) L. Johnson. The sample sites were in the Lansdowne Stat e Forest, New South Wales, Australia and the three tree species were select ed on the basis of their known differential effects on soil. Sampling was c onducted over three seasons, and 79 oribatid and 34 mesostigmatid species w ere identified from 25 196 and 3634 individuals, respectively. Tree species had little effect on mite species composition with only three oribatid spe cies and no mesostigmatid species identified as host-habitat specialists us ing a niche breadth measure. Of mite species found under E. pilularis, E. p ropinqua and A. torulosa trees, 2%, 1% and 0% were defined as host-habitat specialists, respectively. In contrast, tree species had significant and co nsistent effects on mite community structure, which differed in relative ab undance of the oribatid species, their size class distributions and species rankings. In the mesostigmatid communities, there was a difference in the ranking of the mite species among tree species. Although it was demonstrate d that tree species have an impact on the soil environment, the differences between tree species were insufficient to change species composition. The low degree of host-habitat specialization suggested that other factors were more important for determining mite species composition at a site, and soi l mite host-habitat specialization may not make a large contribution to est imates of total global species richness using methods such as those propose d by Erwin (1982).