The decrease in community similarity was examined in corticolous oribatid mites (Acari: Oribatida) sampled along a 36-m vertical profile of 5 western redcedar trees in a temperate rainforest on Vancouver Island, Canada. Samples were collected every 2 m, and all adult oribatid mites were identified to species. When compared to species recorded from previous ground/canopy sampling efforts in the same trees, the 62 corticolous species unequivocally support the separation of these 2 communities at 4m. All sampling heights contained canopy oribatid species, but only 0–4 m communities contained ground-dwelling oribatids. There was significant overall spatial autocorrelation and decay in community similarity with distance originating from species turnover at 4 m, suggesting limited range expansion of ground species into corticolous habitats. Community similarity, richness, and abundance of corticolous oribatid mite assemblages were not autocorrelated after 4 m above ground. Observed patterns at 4 m likely represent an environmental transition zone for ground-dwelling species, such as changes in moisture availability, rather than a physical dispersal barrier for individuals. We conclude that the trunk is not a dispersal corridor for ground species to colonize tree crowns and suggest that low similarity between nearest neighbouring sampling points, combined with the presence of immature and gravid oribatids, supports the assumption that corticolous oribatid mite assemblages are likely dispersal-limited residents.
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Vol. 14 • No. 2