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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Incompatible and compatible plant pathogen interactions

Kathiria, Palak, University of Lethbridge. Faculty of Arts and Science January 2006 (has links)
Pathogens are one of the prevalent stresses to plants. Resistance mediated by the resistance genes is efficient mechanism for evading the pathogens. To understand the influence of various biotic and abiotic factors on resistance gene promoters, plants having N gene promoter fused with reporter genes were developed. Experiments with tobacco plants revealed that on tobacco mosaic virus infection, the N protein may increase in the cells. Also, extreme temperature may result in decrease in the N protein. The salicylic acid produced during the development of systemic acquired resistance does not hinder the N promoter function. Hence, it can be concluded that the promoter region of resistance genes can be influenced by many biotic and abiotic factors. In the tobacco plants lacking the N gene, infection with tobacco mosaic virus leads to generation of systemic recombination signal. Experiments suggest that this signal can lead to better tolerance of the pathogen in next generation. Also, in the plants which received systemic recombination signal, the resistance gene loci are hypermethylated and the frequency of rearrangement in these loci increases. Hence, the signal results in higher tolerance to pathogen and increased genetic variability in resistance genes. / xvi, 147 leaves : ill. (some col.) ; 29 cm.
32

Soft systems analysis of ecosystems

Shanmuganathan, Subana Unknown Date (has links)
This research is a case study evaluation of the use of self-organising map (SOM) techniques for ecosystem modelling to overcome the perceived inadequacies with conventional ecological data analysis methods. SOMs provide an analytical method within the connectionist paradigms of artificial neural networks (ANNs), developed from concepts that evolved from late twentieth century neuro-physiological experiments on the cortex cells of the human brain. The rate and extent at which humans influence environmental deterioration with commensurate biodiversity loss is a cause for major concern and to prevent further degradation by human impact, parsimonious models are urgently needed. Indeed, the need for better modelling techniques has never been so great. Ecologists and many national and international bodies see the situation as 'significantly critical' for the conservation of our global ecosystem to foster the continued wellbeing of humanity on this earth.The thesis investigates and further refines SOM based exploratory data analysis methods for modelling naturally evolving, highly diverse and extremely complex ecosystems. Earlier studies provide evidence on SOM ability to analyse complex forest and freshwater biological community structures at limited scales. On the other hand, growing concerns over conventional methods, their soundness and ability to model large volumes of data are seen as of little use, leading to arguments on the results derived from them. Case study chapters illustrate how SOM methods could be best applied to analyse often 'cryptic' ecosystems in a manner similar to that applied in modelling highly complex and diverse industrial system dynamics. Furthermore, SOM based data clustering methods, used for financial data analysis are investigated for integrated analysis of ecological and economic system data to study the effects of urbanisation on natural habitats.SOM approaches prove to be an excellent tool for analysing the changes within physical system variables and their effects on the biological systems analysed. The Long Bay-Okura Marine Reserve case study elaborates on how SOM based approaches could be best applied to model the reserve's intertidal zone with available numeric data. SOM maps depicted the characteristic microclimate within this zone from ecological monitoring data of physical attributes, without any geographical data being added. This kind of feature extraction from raw data is found to be useful and is applied to two more case studies to study the slow variables of ecosystems, such as population dynamics, and to establish their correlation with environmental variations. SOM maps are found to be capable of distinguishing the human induced variations from that of natural/ global variations, at different scales (site, regional and global) and levels using regional and global data. Hence, SOM approaches prove to be capable of modelling complex natural systems incorporating their spatial and temporal variations using the available monitoring data, this is a major advantage observed with SOM analyses.In the third case study, potential use of SOM techniques to analyse global trends on the effects of urbanisation in environmental and biological systems are explored using the World Bank's statistical data for different countries. Many state and international institutions, concerned over global environmental issues, have made attempts to develop indicators to assess the conditions of different ecosystems. The enhancements with SOM approaches against the currently recommended indicator system based on information pyramid and pressure-state-response (PSR) models are elaborated upon.The research results of SOM methods for ecosystem modelling, similar to that applied to industrial process modelling and financial system analysis show potential. SOM approaches (i.e. cluster, dependent component, decision system and trajectories/ time series analyses) provide a means for feature extraction from the available numeric data at different levels and scales, fulfilling the urgent need for modelling tools to conserve our global ecosystem. They can be used to bridge the gap in converting raw data into knowledge to inform sustainable ecosystem management. Increasingly, traditional methods based on Before-After-Control-Impact (BACI) designs and Analysis of Variance (ANOVA) are seen to be unsuitable for ecological data analysis, as they are unable to detect human induced environmental impacts from that of a natural cause. This thesis proves that SOM techniques could be applied to modelling not only a natural systems complexity but also its functioning and dynamics, incorporating spatial as well as temporal variations, to overcome the constraints with conventional methods as applied in other stated disciplines.
33

Similarities and differences of ecosystems in Mediterranean Australia and Southern Africa, with special reference to infertile sites at the Barrens and the Caledon coast

Antoni Milewski January 1984 (has links)
Similar ecosystems may be expected where climates and landforms on different continents match. The most detailed tests of such convergence have examined mediterranean areas of Europe, North and South America. This thesis compares mediterranean Australia and southern Africa, two relatively nutrientpoor areas largely neglected in previous studies. Inparticular, two study areas very similar in climate, landform and soils were compared, one at the Barrens on the south coast of Western Australia and the other at the Caledon coast in the southwestern Cape of South Africa. The less frequent, but heavier, rain in Australia probably led t o the anomalous presence of trees there. The height and density of vegetation appeared only weakly related to soil nutrients but strongly correlated with moisture. Conversely, nutrient status rather than climate appeared to govern many of those features of plants that interacted with animals, such as flowers and fruits . This applied particularly to ants, which took seeds bearing elaiosomes, and birds, which took fleshy fruits . Soil fertility thus determined the occurrence of agents which both consumed plants and aided their propagation. Climate, soil and fire, together with the consequent regimes of fiutrient cycling and predation, determined the relativeroles played by endotherms, such as mammals, and by ectotherms, such as reptiles, amphibians and their invertebrate prey. Despite close matching, small differences in physical factors remained between the two study areas, with commensurate differences in their biological communities. It is suggested that co-adaptation is not a major cause of differences between ecosystems on different continents but rather a consequence of inevitable differences in physical conditions.
34

Applications of nonequilibrium statistical physics to ecological systems

Guttal, Vishwesha, January 2008 (has links)
Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 123-135).
35

Estimating resilience of Amazonian ecosystems using remote sensing

Oswald, David Nicholas. January 1900 (has links)
Thesis (M.Sc.). / Written for the Dept. of Geography. Title from title page of PDF (viewed 2008/05/28). Includes bibliographical references.
36

Characterizing fish schools in relation to the marine environment and their use by seabirds in lower Cook Inlet, Alaska /

Speckman, Suzann Gail. January 2004 (has links)
Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 125-147).
37

Cross-scale analysis of the Pribilof Archipelago, southeast Bering Sea, with a focus on age-0 walleye pollock (Theragra chalcogramma) /

Ciannelli, Lorenzo. January 2002 (has links)
Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 147-167).
38

EcoSystem-Sim a virtual ecosystem simulator /

Simpson, Roderick F. January 2001 (has links)
Thesis (M.S.)--University of Florida, 2001. / Title from title page of source document. Document formatted into pages; contains x, 60 p.; also contains graphics. Includes vita. Includes bibliographical references.
39

Use of the Biolog system to characterize size fractionated components of an estuarine heterotrophic bacterial community

Moffitt, E. Scott. January 1900 (has links) (PDF)
Thesis (M.Sc.)--Acadia University, 1997. / Includes bibliographical references. Also available on the Internet via the World Wide Web.
40

Use of the Biolog system to characterize size fractionated components of an estuarine heterotrophic bacterial community /

Moffitt, E. Scott. January 1900 (has links) (PDF)
Thesis (M.Sc.)--Acadia University, 1997. / Includes bibliographical references. Also available on the Internet via the World Wide Web.

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