A guide to Oribatid Identification for the ABMI: - Royal Alberta Museum

Almanac of Alberta Oribatida 2.3 13 January 2013Edition of the Manual of Acarology (Krantz & Walter 2009) except the Cohort Astigmata(=Astigmatina, Acaridida), a group of highly derived oribatid mites that has traditionally beengiven its own suborder, is not included.Most described species of oribatid mites inhabit the organic layers of soils (includingsuspended soils in forest canopies) where they feed on microbes, detritus, and smaller, softbodiedinvertebrates such as nematodes. Their comminution of litter, regulation of fungal growthby grazing, and dispersal of microbial propagules are considered important contributions to thefunctioning of the decomposer subsystem in terrestrial ecosystems. Oribatids usually dominatethe abundance and diversity of the soil mesofauna in forest habitats and are prominent ingrasslands, deserts, freshwater habitats, and peatlands (Behan-Pelletier & Bisset 2004; Walter &Proctor 1999; Norton & Behan-Pelletier 2009). Oribatids have proven useful as bioindicators,especially of heavy metal pollution (see Eeva & Penttinen 2009 for a recent review).It seems likely that the oribatid fauna that existed in Alberta before the current ice age began(~60 mya) was exterminated by the ice sheets and the existing fauna has colonized since the icesheets began their retreat (~18,000 bp). Although few oribatid mites are phoretic on insects andmost are assumed to reach new areas primarily by ambulatory dispersal, they rapidly colonizenew disturbed habitats such as the soil exposed by retreating glaciers (Hågvar et al. 2009).Passive dispersal in the feathers of aquatic birds (Krivolutsky & Lebedeva 2004) and catastrophicreleases of meltwater from ice-margin and proglacial lakes (Bedouin & Oetelaar 2003) may havebeen important in the colonization of isolated wetlands. Many of the oribatid mites that thrive intoday’s Albertan climates may have quickly moved north from refugia to the south of the icesheets and later colonized to the southeast from refugia in Berengia. Others, however, may havebeen introduced by early human activities and we undoubtedly continue to introduce new species.but in Alberta only a few species approach 1.0 mm in length. Adult females are typically twicethe body mass of males and about 1.26x as long (Walter & Norton 1984), but many species oforibatid mites have done away with their males and reproduce parthenogenetically (thelytoky).which are covered in Part I below. Part II contains the smaller mites, mostly members of theBrachychthonioidea and Oppioidea, but also including any members of the other superfamilieswhere the adult mites do not exceed the 0.3 mm length test (and records for all other Acariknown from Alberta).Previous research on Alberta’s oribatid speciesPrevious work on Alberta’s oribatid species has been concentrated in the Rocky MountainNatural Region (e.g. the various papers by Mitchell and by Behan-Pelletier in the References),including the outlying Cypress Hills on the Saskatchewan border. Additionally, Lindo & Visser(2004) studied the oribatid fauna at the Ecosystem Management Emulating Natural Disturbance(EMEND) research site approximately 90 km northwest of Peace River (56.46, -118.22),Clapperton et al. (2002) reported on oribatid diversity at Rough Fescue Prairie sites in southernAlberta (the Porcupine Hills near Stavely), and Osler et al. (2008) reported on oribatids in croprotations near Lethbridge (49.48, 112.54). To date, the ABMI 2007-2008 surveys have beenprimarily in the Boreal Forest Natural Region and in some areas of the Aspen Parkland, Foothills,and Grassland Natural Regions (see Map 1), but will eventually cover all of Alberta.10