Scale dependency of dispersal limitation, environmental filtering and biotic interactions determine the diversity and composition of oribatid mite communities

It has long been established that the spatial scale of inquiry affects the ecological patterns that are revealed. However, studies of the ecological drivers underlying the assembly of soil animal communities rarely adopt a multi-scale perspective. Here, we quantified the distribution of oribatid richness along a chronosequence of temperate hardwood forests in a deglaciated region of eastern North America and analyzed variation in oribatid community structure at two grain sizes: 0.1 m2 and 900 m2, and two spatial extents: 20–150 m and 80–420 km. At the largest spatial scale, oribatid richness was similar among sites in the chronosequence. This suggests that oribatid mites faced minimal dispersal limitation during recolonization of deglaciated regions, likely due to long-distance passive dispersal events enabled by their small body size. However, dispersal limitation affected the community assembly at the spatial scale of 80–420 km, whereby the magnitude of dispersal limitation varied with body size and habitat type. Specifically, large-bodied mites in the litter layer experienced a stronger dispersal limitation than did small-bodied ones; and small-bodied mites were limited by dispersal in the mineral soil but not in the litter layer. Environmental filtering, particularly water content in litter and soil, played an important role in shaping oribatid mite communities at both spatial scales. In contrast, competition among oribatid species and biotic interactions with other soil microarthropods appeared to have little influence on oribatid mite community assembly, even within the smallest spatial scale. A majority of the local oribatid assemblages exhibited random coexistence patterns, with a small fraction (14%) of the assemblages exhibiting patterns of segregation consistent with competition among oribatid species. Overall, our study highlights the scale dependency of dispersal limitation during oribatid community assembly, and calls for future comparative studies to encompass a wider range of body size and habitat types.