Graduation date: 1995

Conservation of biodiversity is a major issue in ancient temperate rainforests of British Columbia. While significant efforts have been made to document species of birds and mammals, little is known about canopy arthropod communities in British Columbia. Microhabitats (suspended soils) within canopy systems of temperate rainforests support diverse microarthropod communities, dominated by mites of the suborder Oribatida. These oribatid mite communities are distinct from forest floor communities, contribute significantly to overall forest biodiversity, and are functionally important components of forest ecosystems. I used the suspended soil system in western redcedar trees in the Walbran Valley to study the relative importance of local environmental factors versus regional spatial factors contributing to the structure of arboreal oribatid mite communities. and compare these patterns to forest floor oribatid mite communities at the same study location. An array of sampling methods was used to complete these objectives: substrate core samples. bark scrapings, colonisation of litterbags, litterfall collection, and colonisation of artificial canopy habitats. This study identified 138 species of oribatid mites associated with ancient western redcedar trees of the Walbran Valley on Vancouver Island. The documented patterns of oribatid mite diversity in this rainforest demonstrated higher local species richness (alpha diversity) in terrestrial (forest floor) habitats, and greater beta diversity in arboreal (suspended soil) habitats. The oribatid mite community within suspended soils are formed primarily by dispersal patterns and colonisation within the canopy system. with limited colonisation from the forest floor. The factors, which shape canopy oribatid mite communities within suspended soils, are related to habitat availability, moisture limitation and random dispersal events of individual species. My results suggest the arboreal oribatid mite community experiences regional dispersal limitation associated with physical tree-to-tree dispersal barriers. However, factors other than physical dispersal barriers. such as aggregation and niche partitioning, likely also limit the local distribution of species in both arboreal and terrestrial habitats. Stochastic dispersal dynamics within the canopy are crucial to understanding oribatid mite community structure in suspended soils. yet the relative importance of regional dispersal processes is dependent on deterministic factors relating to the environmental tolerances of individual species at the local scale.

Thesis (DPhil)--University of Stellenbosch, 2008. / ENGLISH ABSTRACT: Sub-Antarctic islands represent the only mid to high latitude terrestrial biomes in the Southern Hemisphere. These islands have various geological origins and histories, well-preserved terrestrial ecosystems and high levels of species endemism. In an attempt to understand the evolution and biogeography of terrestrial taxa in the South Polar Region, the first broad-scale molecular phylogeny was constructed for the unique terrestrial group, the ameronothroid mites (genus Halozetes (Oribatida)), collected from sub-Antarctic and Maritime Antarctic localities. Phylogenetic analyses based on a combined mitochondrial (cytochrome oxidase subunit I (COI)) and nuclear (histone-3 (H3)) sequence dataset indicated that the evolution of these mites were habitat specific (i.e. intertidal, supralittoral and terrestrial). Notwithstanding criticisms levelled against a molecular clock, the mites were evolutionary young (<10myo), contrary to their status as an ancient group predating Gondwana fragmentation. Biogeographic analyses indicated a complex pattern mainly sculpted by multiple independent dispersal events across the Antarctic Polar Frontal Zone similar to previous findings for other marine and terrestrial taxa. Also, the molecular phylogeny displayed considerable discourse with contemporary taxonomy suggesting the need for taxonomic revisions and reassessment of morphological characters. Sub-Antarctic Marion Island, the larger of the two islands comprising the Prince Edward Island archipelago (PEI), has experienced extensive glaciation and volcanism. To assess the impact of historical events (volcanism (including recent eruptions) and glaciation) and contemporary mechanisms (gene flow) on the genetic spatial distribution of species from Marion Island, two mite species namely Eupodes minutus (Prostigmata) and Halozetes fulvus (Oribatida) as well as a single plant species, Azorella selago (Apiaceae), were selected as model organisms. For independent phylogeographic analyses, mitochondrial sequence data (COI) were obtained for both mite species, while chloroplast sequence (trnH-psbA) and amplified fragment length polymorphism (AFLP) data were generated for the cushion plant, A. selago. Since A. selago is typified by two growth forms namely discrete cushions and continuous mats, it was essential to examine the growth dynamics prior to phylogeographic analyses. The sequence and fragment data indicated that both mite and plant species were significantly substructured across Marion Island. Manual comparisons indicated unique populations on the western (Kaalkoppie for H. fulvus, La Grange Kop for E. minutus and Mixed Pickle for A. selago), eastern (Bullard Beach for H. fulvus and Kildalkey Bay for E. minutus), northern (Middelman and Long Ridge for H. fulvus) and southern side (Grey Headed for H. fulvus and Watertunnel for A. selago) of the island. Importantly, the western side had unique localities for all species. Interestingly, based on the H. fulvus data, the western populations were relatively young, characterized by high migration rates, small effective (female) population sizes with no isolation-by-distance. The opposite scenario was found for the eastern populations. This spatial genetic structure described for species on Marion Island can be ascribed to both historical events and environmental conditions. These areas with their unique genetic composition are of special conservational concern; consequently this research will contribute to an active management plan for PEI, South Africa’s only Special Nature Reserve. / AFRIKAANSE OPSOMMING: Sub-Antarktiese eilande verteenwoordig die enigste terrestriële bioom in die middel tot hoër breedtegrades van die Suidelike Halfrond. Hierdie eilande besit ‘n verskeidenheid van geologiese oorspronge en geskiedenisse, goed-bewaarde terrestriële ekosisteme en hoë vlakke van endemisme. In ‘n poging om die evolusie en biogeografie van terrestriële taksa in die Suid Pool Area te verstaan, is die eerste grootskaalse molekulêre filogenie saamgestel vir ‘n unieke terrestriële groep, die ameronothoïed miete (genus Halozetes (Oribatida: Ameronothroidea)), vanaf menigte sub-Antarktiese en Maritime Antarktiese lokaliteite. Filogenetiese analises gebaseer op die saamgestelde mitochondriale (sitokroom oksidase subeenheid I (COI)) en nukluêre (histoon-3 (H3)) basispaarvolgordes het aangedui dat die evolusie van hierdie miete habitat spesifiek is (m.a.w inter-gety, supralitoraal en terrestrieël). Ongeag die kritiek teenoor ‘n molekulêre klok, is hierdie miete evolusionêr jonk (<10mjo), wat teenstrydig is met hulle status as ‘n antieke groep wat terugdateer voor Gondwana fragmentasie. Biogeografiese analises het ‘n komplekse patroon aangedui wat grotendeels gekarakteriseer word deur menigte onafhanklike verspreidingsgebeurtenisse bo-oor die Antarktiese Polêre Frontale Zone, wat ooreenstemmend is met vorige bevindinge vir ander mariene en terrestriële taksa. Die molekulêre filogenie het ook aansienlik verskil van die tradisionele taksonomie, dus is taksonomiese aanpassings en herklassifisering van morfologiese karakters noodsaaklik. Sub-Antarktiese Marion Eiland, die groter eiland van die Prins Edward eilandgroep (PEI), het uitermate glasiasie en vulkanisme ondervind. Om die impak van historiese gebeurtenisse (vulkanisme (insluitend onlangse uitbarstings) en glasiasie) en kontemporêre meganismes (geenvloei) op die genetiesgespasieërde verspreiding van spesies vanaf Marion Eiland te bepaal, was twee mietspesies naamlik Eupodes minutus (Prostigmata) en Halozetes fulvus (Oribatida) asook ‘n enkele plantspesie, Azorella selago (Apiaceae), gekies as model organismes. Vir onafhanklike filogeografiese analises, was die mitochondriale basispaarvolgorde (COI) vir beide mietspesies bepaal, terwyl chloroplast basispaarvolgorde (trnH-psbA) asook geamplifiseerde fragmentlengte polimorfisme (AFLP) data gegenereer was vir die kussingplant, A. selago. Aangesien A. selago gekenmerk word deur twee groeivorme, naamlik diskrete kussings en aaneenlopende matte, was dit noodsaaklik om eers die groeidinamika van die plant te ondersoek alvorens ‘n filogeografiese studie kon geskied. Die basispaarvolgordebepalings en fragmentdata het aangedui dat beide mietspesies sowel as die plantspesie betekenisvolle substruktuur vertoon regoor Marion Eiland. Informele vergelykings het unieke populasies aangedui op die westelike (Kaalkoppie vir H. fulvus, La Grange Kop vir E. minutus en Mixed Pickle vir A. selago), oostelike (Bullardstrand vir H. fulvus en Kildalkeybaai vir E. minutus), noordelike (Middelman en Long Ridge vir H. fulvus) en suidelike kant (Grey Headed vir H. fulvus en Watertunnel vir A. selago) van die eiland. Die westelike kant besit dus unieke lokaliteite vir al die spesies. Interressantheidhalwe het die H. fulvus data getoon dat die westelike populasies relatief jonk is en gekarakteriseer word deur hoë migrasiesyfers en klein effektiewe (vroulike) populasiegroottes met geen isolasie-oor-afstand nie. Die resultate vir die populasies aan die oostelike kant van die Marion Eiland was presies teenoorgesteld. Dié beskryfde substruktuur vir die spesies op Marion Eiland is afkomstig van beide historiese gebeurtenisse asook omgewingstoestande. Hierdie areas met hul unieke genetiese samestelling, is belangrik vir natuurbewaring. Hierdie navorsing sal bydra tot die bestuursriglyne van PEI, Suid Afrika se enigste Spesiale Natuurreservaat.