Spatial Heterogeneity in Ecology

This project predominantly investigated the implications of spatial heterogeneity in the ecological processes of competition and infection. Empirical analysis of spatial heterogeneity was carried out using the lepidopteran species Plodia interpunctella. Using differently viscous food media, it was possible to alter the movement rate of larvae. Soft Foods allow the movement rate of larvae to be high, so that individuals can disperse through the environment and avoid physical encounters with conspecifics. Harder foods lower the movement rate of larvae, restricting the ability of individuals to disperse away from birth sites and avoid conspecifics encounters. Increasing food viscosity and lowering movement rate therefore has the effect of making uniform distributed larval populations more aggregated and patchy. Different spatial structures changed the nature of intraspecific competition, with patchy populations characterised by individuals experiencing lower growth rates and greater mortality because of the reduced food and space available within densely packed aggregations. At the population scale, the increased competition for food individuals experience in aggregations emerges as longer generational cycles and reduced population densities. Aggregating individuals also altered the outcome of interspecific competition between Plodia and Ephestia cautella. In food media that allowed high movement rates, Plodia had a greater survival rate than Ephestia because the larger movement rate of Plodia allowed it to more effectively avoid intraspecific competition. Also the faster growth rate, and so larger size, of Plodia allowed it to dominate interspecific encounters by either predating or interfering with the feeding of Ephestia. In food that restricts movement, the resulting aggregations cause Plodia to experience more intraspecific encounters relative to interspecific, reducing its competitive advantage and levelling the survival of the two species. Spatial structure also affected the dynamics of a Plodia-granulosis virus interaction and the evolution of virus infectivity. Larval aggregation forced transmission to become limited to within host patches, making the overall prevalence of the virus low. However potentially high rates of cannibalism and multiple infections within overcrowded host aggregations caused virus-induced mortality to be high, as indicated by the low host population density when virus is presented. Also aggregated host populations cause the evolution of lower virus infectivity, where less infective virus strains maintain more susceptible hosts within the aggregation and so possess a greater transmission rate. The pattern of variation in resistance of Plodia interpunctella towards its granulosis virus was found using two forms of graphical analysis. There was a bimodal pattern of variation, with most individuals exhibiting either low or high levels of resistance. This pattern was related to a resistance mechanism that is decreasingly costly to host fitness

Conscious and unconscious: passing judgment

The extent to which conscious and unconscious mental processes contribute to our experiences of learning and the subsequent knowledge has been subject to great debate. Dual process theories of implicit learning and recognition memory bear many resemblances, but there are also important differences. This thesis uses subjective measures of awareness to explore these themes using the artificial grammar learning (AGL) and remember/know (R/K) procedures. Firstly, the relationship between response times associated with intuition and familiarity based responding (conscious judgment of unconscious structural knowledge) compared to rule and recollection based responding (conscious structural knowledge) in AGL were found to be strikingly similar to remembering and knowing; their R/K analogues. However, guessing (unconscious judgment knowledge) was also distinct from intuition and familiarity based responding. Secondly, implicit learning in AGL was shown to occur at test, which would not be expected in R/K. Finally, wider theories of cognition, unconscious thought and verbal overshadowing, were shown to have measurable effects on AGL and R/K respectively. The approach used in this thesis shows the merits of both in-depth analysis within a given method combined with the synthesis of seemingly disparate theories. This thesis has built upon the important distinction between conscious and unconscious structural knowledge but also suggests the conscious-unconscious division for judgment knowledge may be as important. Implicit learning and recognition memory tasks differ in the kinds of mental processes that subjective measures are sensitive toward; particularly so in situations where judgment knowledge is unconscious. Different theories and methods divide nature in different ways; the conscious-unconscious judgment distinction may prove an important one

Catalysts, Continuity and Change: Workplace Restructuring in the Chemical Industry

The thesis describes and analyses a long-term transformative change program conducted at ICI (Australia) Botany Site between the years 1987 - 1997. The change program is unusual in that, after a massive and destructive confrontation between management and the unions, a new collaborative approach to change was developed which led to significant organisational renewal. Change interventions developed in the program have diffused through Australian industry over the decade. The program is analysed within the framework of a theoretical model which describes a path taken towards achieving a capable organisation which can sustain productive performance. The thesis uses evidence from the case to investigate issues of management style, governance, flexibility, 'bundled interventions', productivity, work organisation, downsizing, reward systems, skills acquisition and self-managed teams. A theoretical model of organisational change is developed which suggests how the treatment of these contingencies can lead to organisational capability

Does synaesthesia protect against age-related memory loss?

Synaesthesia is known to be linked to enhanced episodic memory abilities, across a variety of stimuli and tests, but the evidence has tended to come from younger adults. This enhanced cognitive ability in early adult life, together with the known brain-related differences linked to synaesthesia (e.g., in both grey and white matter structure), makes it an ideal candidate for exploring the notion of ‘reserve’. That is, synaesthetes may be able to utilise additional cognitive and/or neural resources to mitigate against the effects of age-related decline. This was explored in a 2x2 design contrasting age (young, old) against presence/absence of synaesthesia in two different studies: recognition memory for digits, snowflakes and music; and visual associative learning. Synaesthesia and age had independent, non-interacting, effects on memory ability suggesting that, whilst synaesthetes show a memory advantage and maintain this advantage in later life, the presence of synaesthesia is not able to act as a reserve to protect against the effects of ageing. On our tasks, the benefit of having synaesthesia (enhancing memory) was of a similar magnitude to the effects of age (impairing memory); in other words, elderly synaesthetes present with ‘youthful’ memory abilities. It is important for future research on elderly cohorts to consider the presence of synaesthesia as an individual difference

Challenges and Opportunities for Revegetation in Areas Dominated by Invasive Annual Grasses

Invasive annual grasses (IAG) are a primary ecological threat to sustainability and ecological integrity of rangelands in the western U.S. While availability of effective tools to control IAG is increasing, ensuring compatibility of control practices with other management practices, such as seeding desirable species, is a critical information need. We summarize a series of studies investigating influences of timing, seeding depth, species selection, and planting timing with various herbicides in sites dominated by invasive annual grasses

A five minute interaction made me realise how much I have learnt

After more than two years as a nursing student, I was beginning to experience the additional responsibility that qualifying as a nurse would bring. This sometimes made me doubt my abilities and feel apprehensive about the future

Remote sensing study of land use and sedimentation in the Ross Barnett Reservoir, Jackson, Mississippi area

This multi-year study is aimed at focusing on the recognition of sediment and other affluents in a selected area of the Ross Barnett Reservoir. The principle objectives are the determination of land use types, effect of land use on erosion, and the correlation of sediment with land use in the area. The I2S multi-band imagery was employed in conjunction with ground truth data for both water and land use studies. The selected test site contains approximately forty square miles including forest, open land, and water in addition to residential and recreational areas

Spatial heterogeneity in ecology

This project predominantly investigated the implications of spatial heterogeneity in the ecological processes of competition and infection. Empirical analysis of spatial heterogeneity was carried out using the lepidopteran species Plodia interpunctella. Using differently viscous food media, it was possible to alter the movement rate of larvae. Soft Foods allow the movement rate of larvae to be high, so that individuals can disperse through the environment and avoid physical encounters with conspecifics. Harder foods lower the movement rate of larvae, restricting the ability of individuals to disperse away from birth sites and avoid conspecifics encounters. Increasing food viscosity and lowering movement rate therefore has the effect of making uniform distributed larval populations more aggregated and patchy. Different spatial structures changed the nature of intraspecific competition, with patchy populations characterised by individuals experiencing lower growth rates and greater mortality because of the reduced food and space available within densely packed aggregations. At the population scale, the increased competition for food individuals experience in aggregations emerges as longer generational cycles and reduced population densities. Aggregating individuals also altered the outcome of interspecific competition between Plodia and Ephestia cautella. In food media that allowed high movement rates, Plodia had a greater survival rate than Ephestia because the larger movement rate of Plodia allowed it to more effectively avoid intraspecific competition. Also the faster growth rate, and so larger size, of Plodia allowed it to dominate interspecific encounters by either predating or interfering with the feeding of Ephestia. In food that restricts movement, the resulting aggregations cause Plodia to experience more intraspecific encounters relative to interspecific, reducing its competitive advantage and levelling the survival of the two species. Spatial structure also affected the dynamics of a Plodia-granulosis virus interaction and the evolution of virus infectivity. Larval aggregation forced transmission to become limited to within host patches, making the overall prevalence of the virus low. However potentially high rates of cannibalism and multiple infections within overcrowded host aggregations caused virus-induced mortality to be high, as indicated by the low host population density when virus is presented. Also aggregated host populations cause the evolution of lower virus infectivity, where less infective virus strains maintain more susceptible hosts within the aggregation and so possess a greater transmission rate. The pattern of variation in resistance of Plodia interpunctella towards its granulosis virus was found using two forms of graphical analysis. There was a bimodal pattern of variation, with most individuals exhibiting either low or high levels of resistance. This pattern was related to a resistance mechanism that is decreasingly costly to host fitness.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Using Bayes to get the most out of non-significant results

No scientific conclusion follows automatically from a statistically non-significant result, yet people routinely use non-significant results to guide conclusions about the status of theories (or the effectiveness of practices). To know whether a non-significant result counts against a theory, or if it just indicates data insensitivity, researchers must use one of: power, intervals (such as confidence or credibility intervals), or else an indicator of the relative evidence for one theory over another, such as a Bayes factor. I argue Bayes factors allow theory to be linked to data in a way that overcomes the weaknesses of the other approaches. Specifically, Bayes factors use the data themselves to determine their sensitivity in distinguishing theories (unlike power), and they make use of those aspects of a theory’s predictions that are often easiest to specify (unlike power and intervals, which require specifying the minimal interesting value in order to address theory). Bayes factors provide a coherent approach to determining whether non-significant results support a null hypothesis over a theory, or whether the data are just insensitive. They allow accepting and rejecting the null hypothesis to be put on an equal footing. Concrete examples are provided to indicate the range of application of a simple online Bayes calculator, which reveal both the strengths and weaknesses of Bayes factors