Arboreal oribatid mite diversity: Colonizing the canopy

Thirty-six species of Oribatida (2596 specimens), representing 29 genera and 21 families were recorded from replicated Malaise traps positioned in the canopy and on the forest floor of old-growth Sitka spruce (Picea sitchensis) on western Vancouver Island, Canada, and in an adjacent clear-cut. Traps were sampled bi-weekly throughout the growing season, and colonization was 100% in the canopy, 91% in the forest floor and 47% in the clear-cut. Nine of the species recovered were not recorded from this site using high gradient extractions of moss from canopy or forest floor. Thirty of these species were Brachypylina, with the families Eremaeidae, Peloppiidae and Ceratozetidae represented by three or more species. Colonizing specimens were predominantly adult, and represent sexual taxa: immatures comprised only 0.9-4.2% of specimens. Ceratoppia spp., Eporibatula sp.1, Dorycranosus sp.1, Sphaerozetes sp.1 and Oribatella sp.1 had a frequency >50% in the forest floor traps, and Eporibatula sp.1, Sphaerozetes sp.1 and Dendrozetes sp.1 had a frequency >50% in canopy traps. Phoresy as a source of the oribatid fauna in the Malaise traps is unlikely as, of the species represented, only Paraleius sp.1 is modified for this mode of dispersal. The number of species recorded from the traps, and the frequency, relative abundance, and seasonality of many of them, support the hypothesis that active dispersal by random movement is an important mode of colonization of canopy habitats. (C) 1998 Elsevier Science B.V