This chapter compares oribatid mite biodiversity in tree canopies and litter from three perspectives: components of the faunas, modifications for living in canopy habitats, and ecological roles of these faunas, including implications for ecological processes. In tree canopies, as in litter, Acari dominate the microarthropod fauna, usually exceeding all other arthropod groups in abundance, and competing with insects in terms of species richness. The mite fauna of tree canopies is not just a subset of the litter fauna; it comprises many lineages specific to arboreal microhabitats. Many species appear to have adaptations for living in canopies, perhaps reflecting the different architecture, air movements and general microclimate of canopies in comparison with litter. The range of canopy microhabitats occupied by mites rivals that of the forest floor. The role of litter Oribatida in ecosystem processes includes decomposition, mineralization and development of soil microstructure. The role of components of the canopy oribatid fauna in ecosystem processes may not differ significantly from that in litter, and gut content analyses indicate that resources utilized are broadly similar to those exploited by species in litter. Canopy Oribatida probably help release nutrients sequestered in epiphytes and epiphylls for uptake by the plant. They may also have more complex ecological roles, such as controlling or dispersing leaf fungal pathogens.

Behan-Pelletier, V. M. 2003. Acari and Collembola biodiversity in Canadian agricultural soils. Can. J. Soil Sci. 83: 279-288. In Canadian agricultural soils, mites (Acari) are the most diverse and abundant arthropods. In comparison with other arachnids, mites are notable for their small size, diverse feeding habits, often complex life histories, and the range of habitats in which they live. Collembola are also abundant and diverse in soil and litter, they are in the same size range as the Acari, and for that reason the two groups are often combined in soil ecological studies as "microarthropods". This paper provides a descriptive overview of the state of our knowledge on the taxonomy of these arthropods. It reviews the literature on biology and ecology of microarthropods in Canadian agroecosystems, especially on implications of various agricultural practices for their diversity and population structure. It discusses the research challenges in taxonomy and ecology to address effective use of this biodiversity in Canadian agroecosystems. De taille approximativement identique à celle des acariens, on les combine souvent à eux dans les études sur l'écologie du sol sous l'appellation « micro-arthropodes ». Cet article décrit brièvement l'état de nos connaissances sur la taxonomie de ces arthropodes. L'auteur passe en revue la documentation existante sur la biologie et l'écologie des micro-arthropodes peuplant les écosystèmes agricoles canadiens, en particulier les répercussions des multiples pratiques agricoles sur la diversité et la structure de la population de ces organismes. Il y est question des enjeux de la recherche en taxonomie et en écologie qui permettront une exploitation efficace de cette biodiversité dans les écosystèmes canadiens.

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