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

Abstract Erwin’s method for estimating total global species richness assumes some host‐specificity among the canopy arthropods. This study examined possible host habitat specialization in two major groups of soil arthropods, the oribatid and mesostigmatid mites, by sampling beneath three tree species: Eucalyptus pilularis Smith, Eucalyptus propinqua Deane and Maiden and Allocasuarina torulosa (Aiton) L. Johnson. The sample sites were in the Lansdowne State Forest, New South Wales, Australia and the three tree species were selected on the basis of their known differential effects on soil. Sampling was conducted over three seasons, and 79 oribatid and 34 mesostigmatid species were identified from 25 196 and 3634 individuals, respectively. Tree species had little effect on mite species composition with only three oribatid species and no mesostigmatid species identified as host‐habitat specialists using a niche breadth measure. Of mite species found under E. pilularis , E. propinqua and A. torulosa trees, 2%, 1% and 0% were defined as host‐habitat specialists, respectively. In contrast, tree species had significant and consistent effects on mite community structure, which differed in relative abundance 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 demonstrated 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 soil mite host‐habitat specialization may not make a large contribution to estimates of total global species richness using methods such as those proposed by Erwin (1982).