Active dispersal of oribatid mites into young soils

Soil organisms contribute considerably to soil formation, fertility and microstructure of young soils. Oribatid mites as a part of the soil mesofauna are able to colonize young soils within a few years, but little is known about their dispersal pathways. In particular, the role of active dispersal during the colonization of young soils is almost unknown. The aims of the present study were (1) to determine the distance of active above-ground dispersal by oribatid mites in bare test plots with pure substrate using mini-pitfall traps in different distances to the source substrate (meadow), (2) to determine active below-ground movement using minicontainer traps in different distances to the meadow, (3) to calculate species-specific dispersal rates, and (4) to compare the contribution of wind-dispersal (investigated in a former study) as well as active above- and below-ground movement to the species assemblage dispersing into the bare plots. The results demonstrate that active migration occurs both above- as well as below-ground. From 31 species in the adjacent meadow, 17 immigrated into the bare test plots. The number of specimens and species actively moving above-ground significantly decreased with increasing distance along the bare substrate. Dispersal rates were species specific and varied between 0.3 and 2.1 cm/day. The number of specimens actively moving below-ground was low. However, relative to the low specimen number the number of species was high. Particularly members of the Suctobelbidae and Oppiidae actively moved into the bare plots below-ground. Dispersal mechanisms were found to be species specific, as about 32% of the registered species moved actively below-ground, 32% moved actively above-ground and about 26% combined active movement and passive wind-dispersal. In conclusion, active dispersal is an important dispersal mechanism in the colonization of young soils. However, several species combine different dispersal mechanisms, so that the number of possible dispersal pathways is one factor that determines specimen- and species-richness in a newly found habitat. (C) 2011 Elsevier B.V. All rights reserved.