Geographic ecology of soil oribatid mites in deciduous forests

On a broad, geographic scale (Belgium), soil oribatid mites show relatively simple patterns of spatial distribution and habitat use since 2 groups of species can be defined: "regionally specialist' (RS) species which are rare and restrict their humus type occupancy, and "regionally generalist' (RG) species with reverse attributes. In the locality studied, 7/31 RS species inhabited all or nearly all the stands sampled and used widely disjunctive categories of habitat resources taking into account vertical location within organic layers (litter or humus), humus type (mor or moder) and vegetation (climax or secondary) developed in the study site. Nevertheless, their overlap on these categories was lower on average than the one of the 20 RG species which did not change their patterns on both geographic scales. Some of the 34 other RG species narrowed their local distribution and showed a clear specialization on the habitat categories. To explain the local/regional variations of patterns, it is proposed to interpret the regional distribution shown by soil oribatid mites in terms of tolerance to environmental factors. Then, it is advocated, the role of biotic interactions in the local widening of habitat breadth shown by the RS as well as RG species, and to produce a local non-equilibrium assemblage. -from Authors