Metacommunties are sets of interacting species embedded in landscapes and interconnected via dispersal. The development of metacommunity theory has greatly outpaced its experimental testing. This situation restricts the feedbacks between theory and natural systems, hindering the development of useful theory and limiting application of theory to natural patterns. My dissertation aims to accelerate the testing of metacommunity theory using three microcosm experiments ranging from highly to more loosely constrained. The first experiment implemented a competition-colonization tradeoff between two strains of bacteria and tested if the tradeoff produced the expected patterns of coexistence and ecosystem function. Generally, the results conformed closely to theoretical expectations, though high stochasticity limited coexistence. The second experiment utilized multi-trophic protist communities to test if assembly history followed by complete mixing can produce situations where one community replaces another. Results indicate that community replacement can occur under mixing, though it may be buffered by trophic structure. The third experiment tested the ability of variance partitioning to attribute landscape patterns to process in a one-predator two-prey system. Results indicate that both predators and dispersal can generate similar spatial patterns. Distinguishing between the two requires explicitly incorporating the predator into the partition. In summary, each of these three experiments reinforces aspects of existing theory while illuminating new paths for future theoretical and empirical exploration. / text

Inaug.-dis.--Bern.

No description available.

This paper is to present a study of ultrastructured elements of the microcosm as a stimulus for painting.

In this study, total As (T-As) levels in superpermafrost groundwater at a site in the High Arctic doubled over the course of the summer thaw. This increase was not due to snow input, as levels in snow were negligible. This increase in T-As did not correspond with a decrease in Eh, nor a rise in soluble Fe(II). It did, however, correspond with a shift in As speciation from arsenate to arsenite suggestive of reducing conditions. In the absence of predominant reducing conditions, the highly alkaline nature of the melting snow and concomitant large input of HCO3- may have played an important role in the increase of As in groundwater during the summer thaw. <p>Laboratory studies found that dissolved As (D-As) release under anaerobic conditions depended on the organic matter content of soil, with organic soils releasing D-As under reducing conditions and mineral soils sequestering D-As. In temperate soils, the release of D-As from organic soils is greatly accelerated due to the activity of anaerobic microbes. In northern soils, the same phenomenon may occur, with greater microbiological activity in organic soils where there is more labile C and nutrients than in mineral soil. <p>The sequestration of As in mineral soil is postulated to have occurred due to preferential sorption of arsenite to ferrihydrite or possibly to green rust minerals present under anaerobic conditions. Supporting this, arsenite sequestration occurred to a greater extent compared to arsenate, which is in agreement with the relative affinities of these two species for ferrihydrite. <p>Evidence from this study suggests that the As cycle on Truelove Lowland is dominated by the desorption of As due to HCO3- input each year during the spring melt linked to the sorption of As to ferrihydrite or green rust present in underlying mineral soils. The sequential thawing of the soils active layer and large inputs of HCO3- are unique to northern environments. Thus, this delicate balance of two sorbing processes should be born in mind in northern development. Large inputs of soluble organic matter or nutrients could cause increased solubilization and mobility of D-As during the summer thaw when soils become flooded.

In this study, total As (T-As) levels in superpermafrost groundwater at a site in the High Arctic doubled over the course of the summer thaw. This increase was not due to snow input, as levels in snow were negligible. This increase in T-As did not correspond with a decrease in Eh, nor a rise in soluble Fe(II). It did, however, correspond with a shift in As speciation from arsenate to arsenite suggestive of reducing conditions. In the absence of predominant reducing conditions, the highly alkaline nature of the melting snow and concomitant large input of HCO3- may have played an important role in the increase of As in groundwater during the summer thaw. <p>Laboratory studies found that dissolved As (D-As) release under anaerobic conditions depended on the organic matter content of soil, with organic soils releasing D-As under reducing conditions and mineral soils sequestering D-As. In temperate soils, the release of D-As from organic soils is greatly accelerated due to the activity of anaerobic microbes. In northern soils, the same phenomenon may occur, with greater microbiological activity in organic soils where there is more labile C and nutrients than in mineral soil. <p>The sequestration of As in mineral soil is postulated to have occurred due to preferential sorption of arsenite to ferrihydrite or possibly to green rust minerals present under anaerobic conditions. Supporting this, arsenite sequestration occurred to a greater extent compared to arsenate, which is in agreement with the relative affinities of these two species for ferrihydrite. <p>Evidence from this study suggests that the As cycle on Truelove Lowland is dominated by the desorption of As due to HCO3- input each year during the spring melt linked to the sorption of As to ferrihydrite or green rust present in underlying mineral soils. The sequential thawing of the soils active layer and large inputs of HCO3- are unique to northern environments. Thus, this delicate balance of two sorbing processes should be born in mind in northern development. Large inputs of soluble organic matter or nutrients could cause increased solubilization and mobility of D-As during the summer thaw when soils become flooded.

In the modern ocean, manganese is oxidized over a timescale of days. To better understand the mechanisms and driving factors for manganese oxidation in the natural environment, experiments were performed with surface water samples collected from the San Antonio Bay. In this study area, the formaldoxime assay was utilized to determine that manganese oxidation is catalyzed via multiple pathways utilizing various catalysts and proximal oxidants. The contribution of catalysts such as colloidal matter, microorganisms and the proximal oxidant superoxide were investigated in the San Antonio Bay. The study suggests that superoxide contributed about 30% of Mn oxidation. The microorganisms and colloids were equal in terms of catalysis and accounted for approximately 100% of Mn oxidation. This study is important because gaining more understanding on the mechanisms by which Mn is oxidized will contribute to its use as a geochemical redox indicator.

Microbicides are used in consumer products worldwide to enhance their antibacterial potency in disinfection, for antisepsis or as preservatives. With the widespread use of these compounds, concerns have been expressed about their potential to select for reduced susceptibility. Whilst in vitro studies have reported the laboratory generation of bacterial insusceptibility for certain combinations of bacterium and microbicide, true microbicide resistance, which is defined as a change in susceptibility that is likely to affect the outcome of treatment, has not been frequently reported or observed in the environment. Importantly, risk assessments on the use of microbicides have been largely based on laboratory studies whereby pure cultures of bacteria are exposed to microbicides in aqueous solution. In use however, microbicides are formulated with various excipients and bacteria are exposed to them most commonly in complex biofilm communities. Work described in this doctoral thesis evaluates the effects of exposing bacteria to microbicides using exposure conditions intended to increase realism, with the ultimate aim of informing improved risk assessment methods that better reflect deployment of microbicides in the real-world, taking in to account the effects of formulation, growth in multi-species communities and potential reduced competiveness in adapted bacteria. Test bacteria (8 species, 7 genera) were repeatedly exposed to selected microbicides in aqueous solution and in various formulations reflecting their use in the domestic environment, such as general-purpose cleaners and laundry detergents. Minimum inhibitory concentrations, minimum bactericidal concentrations and minimum biofilm eradication concentrations were determined before and after 14 passages (P14) in the presence of microbicides (benzalkonium chloride (BAC), benzisothiazolinone (BIT), chlorhexidine (CHX), didecyldimethyl ammonium chloride (DDAC), Glydant (DMDM-hydantoin), polyhexamethylene biguanide (PHMB), thymol and triclosan) in aqueous solution or in formulation, using a previously validated gradient plating system. Bacteria were subsequently passaged a further 14 times in the absence of any antimicrobial agent to determine the stability of any adaptations (X14). In bacterial isolates that demonstrated marked changes in susceptibility, further phenotypic analysis was conducted to test for any induced alterations in antibiotic susceptibility, planktonic growth rate, biofilm formation, competitive fitness and relative pathogenicity. Exposure of microbial communities was carried out using a previously validated domestic drain biofilm simulator within constant depth film fermenters (CDFF). The CDFFs were exposed to increasing concentrations of BAC in aqueous solution or BAC formulation over a 32-week period. Changes in bacterial community composition and antimicrobial susceptibility distributions were assessed via replica plating onto selective and antimicrobial-containing agars as well as through the use of next generation sequencing technologies via the illumina Miseq platform and QIIME software. The formulation of microbicides significantly increased antibacterial and anti-biofilm potency and reduced the incidence and extent of the development of insusceptibility isolated bacteria (7 non-revertible bacteria in MBCs for microbicides, whilst 2 non-revertible bacteria in MBCs for formulations). In bacteria that develop marked changes in antimicrobial susceptibility after repeated exposure show changes to biofilm growth rates (10 increases and 6 decreases after microbicide exposure; 1 increase and 3 decreases after formulation exposure), as well as alterations in competitive fitness (6 decreases and 19 increases after microbicide exposure; whilst all exposed to formulation had decreased fitness) and virulence (9/13 decreased and 1/13 increased after microbicide exposure; 4/7 decreased and 2/7 increased after formulation exposure). In the multispecies microcosm system, long-term exposure to BAC or BAC formulation induced shifts in bacterial community dynamics and resulted in a decrease in BAC and various antibiotic susceptibilities (1 log10 reduction in the BAC system; 2.5 log10 reduction in the BAC formulation system of viable bacteria). Such shifts in community dynamics after antimicrobial treatment are theorised to be mainly due to clonal expansion of innately insusceptible bacteria (abundance of Achromobacter sp. increased by 39% in BAC system and 10% in BAC formulation system). Understanding the potential selectivity of microbicide-containing formulations is likely to better serve by testing formulations as well as actives in aqueous solutions. This highlights the need to conduct risk assessments of induced microbicide susceptibility changes using conditions that more accurately reflect their deployment.

The interaction of microorganisms with sediments can enhance their survival by reducing exposure to various stressors and thus marine sediments may act as reservoirs for pathogenic microorganisms. In coastal waters there can be an increased risk of infection to humans due to the possible re-suspension of these microorganisms during recreational activities. This research attempts to more accurately identify environmental exposure in the first stage of a health risk assessment in recreational coastal waters. Techniques were developed to successfully separate microorganisms from sediment particles. Of the methods investigated, subjecting diluted sediment samples to a sonication bath for 10 minutes was found to be the most efficient separation technique over a range of sediment types. This method was therefore used in the subsequent studies to enumerate organisms from the surface sediment layer, as distinct from the water column. Faecal coliforms were enumerated by membrane filtration in both water and sediment from three Adelaide metropolitan recreational coastal sites, chosen to represent different physical sediment characteristics, over a 12-month period. All sites investigated met current National Health and Medical Research Council Guidelines for primary contact recreation. Faecal coliform concentrations were generally greater in sediment compared with overlying water for all samples. This was most evident in sediment consisting of greater silt/clay and organic carbon content (with up to 1000 times higher concentrations in the surface sediment layer compared with overlying water). For coastal recreational sites impacted by stormwater or river discharges, high faecal coliform concentrations were found to be associated with rainfall. A laboratory-based microcosm study utilising intact sediment cores was undertaken to determine the decay rates of faecal indicator organisms (E. coli, enterococci and somatic coliphage) and pathogens (Salmonella derby and S. typhimurium) in both overlying water and in various sediment types. For all organisms tested, temperature had an inverse relationship with survival. Greater decay was observed in the overlying water compared to the surface sediment layer. Small particle size and high organic carbon content was found to be more conducive to microbial survival. In general, decay rates of E. coli were significantly greater than enterococci and coliphage. Although no significant correlations were observed between decay rates of the pathogens and indicator organisms, decay of Salmonella spp. in overlying water more closely resembled that of E. coli than that of other indicators. Using decay rates measured in the microcosm study and available dose-response data, a quantitative microbial risk assessment (QMRA) utilising Monte Carlo simulation was undertaken to estimate the risk of infection to Salmonella spp. and rotavirus following exposure to recreational coastal water subject to a range of faecal contamination levels. For modelling purposes, the assumption was made that rotavirus decay was equivalent to coliphage decay. The probability of infection from rotavirus due to exposure to contaminated recreational coastal water was greater than that for Salmonella spp. under all scenarios. This increased probability of infection is linked to the high infectivity of rotavirus compared to Salmonella spp. Results of this research highlight the limited effectiveness of using prescribed faecal coliform concentrations in the water column alone to estimate the risk of exposure to pathogenic microorganisms during recreational activity at coastal areas. It demonstrated that coastal sediments act as a reservoir for both indicator and pathogenic organisms released into the coastal environment. This suggests an increased exposure risk if these organisms are resuspended back into the water column during recreational activity. A combined risk-based monitoring program would provide a more robust and reliable estimate of health risk associated with coastal recreational areas.

Despite research on the school principalship having evolved over past decades, the prevailing standpoint has largely remained an outsider's perspective upon external behavioural manifestations of principalship. Whilst valuable in their own right, such models of research accord little importance to the effect of thought and intention on behaviour. The purpose of this research was to articulate the notion of a principal's "microcosm" as a means of capturing the dynamics of meaning making in the principalship, when the cognitive world of the principal and the actual work of school leadership interact. The functional context was the expectations of catholic school authorities that schools will engage in processes of continuous self-renewal. Following comprehensive analysis of recent theoretical and research literature, a preliminary framework for the principal's microcosm was generated. A single-investigator, multiple-site case study methodology was utilised to conduct the field research, which was carried out in a provincial city of an Australian state. Three principals were selected as the subjects for in-depth exploration and analysis over a period of 16 months. A range of qualitative research strategies was employed, encompassing formal and informal interactions with the three principals and selected members of their professional communities. On the basis of the field study, a refined framework for the principal's microcosm was developed. Four major conclusions were identified. First, the notion of microcosm offers promise as an explanatory and analytical tool for focussing upon the complexities of change in school settings. Second, metaphor was observed to be integral to microcosm and its usefulness for comprehending leader behaviours was identified. The third conclusion concerned the potential of the construct microcosm for facilitating leader development through assisting individual leaders to reflect upon and to critically examine personal meanings embedded within their own professional practice. Finally, this research makes a contribution to clarifying the nature of catholic education itself.