Habitat specificity of mites on sub-Antarctic Marion Island

Studies on sub-Antarctic insects have suggested that species inhabiting the epilithic biotope (cryptogam-dominated habitats) exhibit higher habitat specificity than those species of the vegetated biotope (habitats dominated by vascular plants), and that this is partially the consequence of recolonization of the latter by migration from the former, which acted as glacial refugia during the Neogene. Here, the Acari is used to independently test this idea. To do so, 17 different habitats belonging to both the epilithic and vegetated biotopes were quantitatively sampled on sub-Antarctic Marion Island. These habitats included those on a rocky shore zone, in lowland vegetation, and in a mid-altitude fellfield. Thirty-nine morphospecies/taxa from 27 families were recorded, with a maximum abundance exceeding 300,000 individuals/m(-2). Mite assemblages differed significantly between all habitats, although the most pronounced differences were between the rocky shore, fellfield epilithic, and vegetated biotope habitats. Major differences between the rocky shore and fellfleld habitats indicated that a clear distinction must be drawn between these two groups of habitats, although both were previously considered part of the epilithic biotope. It seems likely that the mite fauna of the vegetated biotope was derived mostly from fellfield habitats following deglaciation. Habitat specificity, was also more pronounced in the epilithic (rocky shore and fellfield epilithic) species than in those from the vegetated biotope. Thus, the Acari provide support for the hypothesis of reduced habitat specificity in vegetated biotopes, possibly as a consequence of recent recolonization.