Thesis (Ph. D.)(Pasture Science)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Deserts comprise the largest terrestrial biome, making up approximately one third of the Earth’s land mass. They are defined in terms of moisture deficit using the Aridity Index with values <1. A further delineation based on mean annual temperatures into hot (>18°C), cold (<18°C) and polar (<0°C) deserts is employed. In the absence of significant macrobiota, microorganisms are key to desert ecosystems. They are located in near-surface soils, and include a widespread hypolithic mode of colonization, where microbial biomass develops on the ventral surfaces of quartz and other translucent stones. A literature review was conducted to appreciate the status of existing knowledge on these systems. Amongst unresolved questions that arose were the following, which form the basis of this inquiry: What are the taxonomic and functional differences between hypolithic and near-soil communities? Do hypolithic communities assemble differently in deserts of different xeric and thermal stresses? Can the keystone cyanobacterial taxa be cultivated under laboratory conditions to allow manipulative studies? The Mojave Desert in the USA was used as a model to test the extent to which hypolithic and near-surface soil communities vary in both taxonomic and putative functional composition. A common phylogenetic marker (16S rRNA gene ITS region) was used to conclude that soil and hypolithic communities are significantly different, although both were dominated by cyanobacteria. The ubiquitous hypolithic cyanobacterial taxon Chroococcidiopsis was encountered, although communities appeared to be dominated functionally by the diazotrophic genus Nostoc. The data strongly suggest that carbon and nitrogen fixation pathways in desert soils are mediated by the same taxa, although heterotrophic pathways may differ and support distinct assemblages of heterotrophic bacteria. An opportunistic sampling of three sites along a latitudinal gradient in China allowed some inference about adaptations in hypoliths. Communities recovered from the cold Tibetan Desert, Taklamakan Basin Desert, and exposed hillsides in tropical Hong Kong, did not display significant differences at the level of community assembly. This suggests that hypolithic taxa undergo strong selection for xeric and extreme thermal stresses. A cultivation strategy for the keystone taxon Chroococcidiopsis has been lacking and is an obvious impediment to manipulative physiological studies. Here various methods for laboratory cultivation were attempted. This bacterium proved extremely fastidious and displayed slow growth rates. After extensive trials a novel cultivation method was developed. This involved using plastic petri dishes containing liquid growth medium, into which glass coverslips were introduced along with cell suspensions. The surface energy of glass served as a nucleation site for Chroococcidiopsis biofilms (which do not develop on plastic surfaces) and this method was evaluated in growth studies as a means of quantifying growth. This research includes key advances to demonstrate that hypoliths and soil, whilst supporting different communities, likely perform similar functional roles in the desert soil. Selection due to the severe environmental stresses results in similar communities across large latitudinal and environmental gradients. The development of a cultivation strategy paves the way for manipulative physiological studies on these important organisms. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

No description available.

This master’s paper analysis the unemployment rate and its differentiation in regions. The comparison is made with other Baltic states in order to establish the main differences between the magnitude of index and its regional variation. The paper studies how the speed of labour force reallocation between sectors influences the unemployment rate in Lithuania and estimates whether the Lithuanian data cerrespond to the basic principles of the theories explaining unemployment in transitional economics. A thorough examination of the reasons of the level of differentiation was made which covered three stages. Regions, using cluster analysis, were grouped according to four main economic indicators in three years. It was compared how the changes of distribution relate with the changes of the regional unemployment rates. It was analysed how the unemployment rate depends upon the structure of the employed according to economic activities, also identified the basic economic and social factors having influences on the regional unemployment rates. In this research the perspective dynamics of unemployment rate in Lithuania and its regions are foreseen.

No description available.

Satellite images have been used as a complementary information for geological studies. In order to realise the maximum potential of satillite imagery, then improvements are needed, both in the visual presentation of such images, and in their automatic classification , in order to reveal the rock differences. Methods of processing imagery, were evaluated (band ratio, principal components, decorrelated stretch and maximum likelihood) and new (canonical regression, hue-saturation-intensity HSI transform, with modified manipulation, and watershed) were evaluated with respect to their ability to reveal rock differences. It was found that the HSI method gave the best results, both for visual presentation and automatic classifcation. This method has the ability to enhance both spectral and spatial information simultaneously without any data loss which is not the case in the other image enhancement methods (band ratio, principal components or decorrelation stretch). For automatic classification, the 'hue' images produced by the HSI transformation typically gave accurate (91%) classification of all the major rock types. Further, it was shown that the watershed method of classification was superior error rate = 9% to the maximum likelihood method (error rate 14%) for the same inputs. The new method of canonical regression was evaluated and although it was not very successful, the results were encouraging and it was concluded that this method may enable the estimation of the chemical composition of exposed rocks directly from satellite imagery.

No description available.

No description available.

Thesis (M.Env.St.) - Dept. of Environment Studies, University of Adelaide, 1978. / Typescript (photocopy).

Thesis (Ph.D.) -- La Trobe University, 2007. / Research. "A thesis submitted in total fulfillment of the requirements for the degree of Doctor of Philosophy, Department of Botany, School of Life Sciences, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora". Includes bibliographical references (leaves 173-187). Also available via the World Wide Web.