In the present work we study multivariate extreme value theory. Our main focus is on exceedances over linear thresholds. Smaller part is devoted to exce- edances over elliptical thresholds. We consider extreme values as those which belong to remote regions and investigate convergence of their distribution to the limit distribution. The regions are either halfspaces or ellipsoids. Working with halfspaces we distinguish between two setups: we either assume that the distribution of extreme values is directionally homogeneous and we let the halfspaces diverge in any direction, or we assume that there are some irre- gularities in the sample cloud which show us the fixed direction we should let the halfspaces drift out. In the first case there are three limit laws. The domains of attraction contain unimodal and rotund-exponential distributions. In the second case there exist a lot of limit laws without general form. The domains of attraction also fail to have common structure. The similar situation occurs for the exceedances over elliptical thresholds. The task here is to investigate convergence of the random vectors living in the complements of ellipsoids. For all, the limit distributions are determined by affine transformations and distribution of spectral measure. 1

The Auditory Steady State Response (ASSR) procedure has been established as a frequency specific, objective audiologic measure, which can provide reliable thresholds to within 10 dB of the behavioral thresholds. In order for ASSR to find its place in the existing framework of audiometric procedures, the full potential of the procedure needs to be explored. The aim of this study was to determine the accuracy of monotic ASSR in estimating hearing thresholds in a group of 15 normal hearing subjects and 15 hearing-impaired subjects. A comparative research design was implemented. Indicating that results obtained in the study was compared to relevant literature where dichotic multiple ASSR was implemented. This was done in order to ascertain ASSR’s capabilities with regard to stimulus presentation methods. Monotic single ASSR predicted behavioural thresholds in the normal hearing subjects within an average of 24 dB across the frequency range (0.5, 1, 2&4 kHz). In the hearing-impaired group, ASSR thresholds more closely resembled behavioural thresholds, with an average difference of 18 dB, which is consistent with recent literature. The literature suggests that better prediction of behavioural thresholds will occur with greater degrees of hearing loss, due to recruitment. The focus in this group also centered on the accurate prediction of the configuration of the hearing loss. It was found that ASSR could reasonably accurately predict the configuration of the hearing loss. In the last instance, monotic single and dichotic multiple ASSR were compared with regard to threshold estimation and prediction of configuration of the hearing loss in the hearing-impaired group. Little difference was reported between the two techniques with regard to the estimation of thresholds in both the normal hearing and hearing impaired groups. In conclusion it was established that monotic ASSR could predict behavioural thresholds of varying degrees and configurations of hearing loss in normal and hearing-impaired subjects with a reasonable amount of accuracy. At this stage, however, more research is required to establish the clinical validity of the procedure, before it is routinely included within an objective test battery. / Dissertation (M (Communication Pathology))--University of Pretoria, 2005. / Speech-Language Pathology and Audiology / Unrestricted

This research reports on the use of the resilience assessment approach to evaluate the social-ecological systems (SES) at the NWU (Vaal) for a nine month period from March 2013 to November 2013. The research aims to determine the merits of the use of a resilience assessment approach to determine the resilience of the NWU (Vaal) in respect of social-ecological systems. Objectives of the research include the identification of disturbing events to environmental resilience, to construct a conceptual social-ecological systems model of the NWU (Vaal) in order to determine thresholds relevant to resilience and to determine if the resilience assessment approach can be applied at the NWU (Vaal). Data was collected in the form of a literature review, which aided with the construction of a time line for the focal social-ecological system; document reviews, interviews with relevant role players, observation by the researcher and the use of the assessment approach to construct the social-ecological system model. The research findings include identification of possible disturbances and thresholds relevant to resilience of the social-ecological system of the NWU (Vaal). The construction of a social-ecological system model of the NWU (Vaal) aids with proposals to incorporate a stewardship approach which enhance resilience of the focal social-ecological system. / M (Environmental Management), North-West University, Potchefstroom Campus, 2015

This research reports on the use of the resilience assessment approach to evaluate the social-ecological systems (SES) at the NWU (Vaal) for a nine month period from March 2013 to November 2013. The research aims to determine the merits of the use of a resilience assessment approach to determine the resilience of the NWU (Vaal) in respect of social-ecological systems. Objectives of the research include the identification of disturbing events to environmental resilience, to construct a conceptual social-ecological systems model of the NWU (Vaal) in order to determine thresholds relevant to resilience and to determine if the resilience assessment approach can be applied at the NWU (Vaal). Data was collected in the form of a literature review, which aided with the construction of a time line for the focal social-ecological system; document reviews, interviews with relevant role players, observation by the researcher and the use of the assessment approach to construct the social-ecological system model. The research findings include identification of possible disturbances and thresholds relevant to resilience of the social-ecological system of the NWU (Vaal). The construction of a social-ecological system model of the NWU (Vaal) aids with proposals to incorporate a stewardship approach which enhance resilience of the focal social-ecological system. / M (Environmental Management), North-West University, Potchefstroom Campus, 2015

Failure of slopes adjacent to the UK transport infrastructure causes delays and these are expensive assets to repair and maintain. Understanding the processes that lead to failure will assist asset managers both now and in the future in the context of a changing climate. The EPSRC-funded multidisciplinary FUTURENET project investigated the effect of climate change on the resilience of the UK transport network and this thesis is a part of that project considering the weather patterns leading to slope failures along transport infrastructure slopes within the UK. To that end a series of slope failure case studies were investigated to understand the processes leading to failure. These were compiled using nationally held datasets as well as news reports. This research used data from the FUTURENET partners that hold national data sets and asset management information. This shows the wide reaching remit of a multidisciplinary collaborative project such as FUTURENET, but also highlights the limitations of datasets collected and used for very specific purposes and not necessarily suited to wider research. From these case studies a suite of slope failure weather thresholds were developed. These thresholds consider the antecedent period, water content within the slope through the soil moisture deficit and triggering rainfall through comparison to the long term average rainfall. Consideration was given to possible future weather using weather event sequences (WESQs), possible weather patterns for 2050 derived from the UKCP09 climate projection data. By considering these possible weather patterns with the slope failure thresholds a picture of a possible future was evaluated.

The present paper provides first microlevel (indirect) empirical evidence on changes in the determinants of firm profitability, the role of fixed and sunk costs, as well as the nature of competition for a transition economy. We estimate size thresholds required to support different numbers of firms for four retail and professional service industries in a large number of geographic markets in Slovakia. The three time periods in the analysis (1995, 2001 and 2010) characterize different stages of the transition process. Specific emphasis is given to spatial spill-over effects between local markets. Estimation results obtained from a spatial ordered probit model suggest that entry barriers have declined considerably (except for restaurants) and the intensity of competition has increased. We further find that demand spill-overs and/or the effects associated with a positive correlation in unobservable explanatory variables seem to outweigh negative spill-over effects caused by competitive forces between neighboring cities and villages. The importance of these spatial spill-over effects differs across industries. / Series: Department of Economics Working Paper Series

Behandelt werden zufällige lineare Gleichungssysteme modulo 3, wobei in jeder Gleichung genau k Variablen vorkommen. Es wird gezeigt, dass der Schwellwert der Lösbarkeit solcher Gleichungssysteme bei der 2-Kern-Dichte von 1 liegt. Das Resultat ist eine Verallgemeinerung bereits bekannter Resultate für den modulo 2 Fall. Dabei entsteht der 2-Kern dadurch, dass wir alle Variablen mit nur einem Vorkommen löschen. Die Dichte ist definiert als der Quotient der Anzahl der Gleichungen durch die Anzahl der Variablen. Im Rückblick ist dieses Resultat ein natürlicher Schwellwert und die Vermutung liegt nahe, dass er bei analogen Situationen über anderen Strukturen als Z3 auch gelten sollte. Allerdings sind schon im modulo 2 Fall die analytischen Probleme nicht gering, und der hier behandelte Fall braucht weitere analytische Einsichten.

Aquatic ecosystems are especially vulnerable to human impacts associated with agricultural land-use, which provide multiple stressors altering community composition, important ecosystem functions and human valued properties of freshwaters. However, the increased occurrence of excessive levels of nitrate-nitrogen has raised major concerns about toxicity and stress on aquatic life, especially in regions such as the Canterbury Plains, New Zealand. The aims of this thesis were to identify nitrate-nitrogen effects on stream communities, and additionally provide field data to inform proposed national bottom lines for nutrients in New Zealand streams. A field survey was conducted on 41 small streams on the Canterbury Plains spanning a nitrate-nitrogen gradient (mean 0.4 – 11.3 mg/L). Spot nitrate-nitrogen was collected during and after the field survey to measure temporal variation in stream nitrate-nitrogen concentration for six months. This showed nitrate-nitrogen concentration varied between season and sub-region, where concentrations increased in winter and Ashburton had higher nitrate-nitrogen than Rangiora and Lincoln, respectively. These regimes of nitrate-nitrogen showed similar patterns in mean, median and maximum concentrations. To be confident my spot nitrate-nitrogen provided a true representation of long-term water chemistry, I compared Environment Canterbury 12 monthly data with my six monthly data in a sub-set of 15 sites. This comparison showed similar nitrate-nitrogen patterns and range of values between the two datasets. I then compared 12 common benthic invertebrate biotic metrics with my nitrate-nitrogen data and found none were correlated with this contaminant. For example, the Macroinvertebrate Community Index and quantitative variant (QMCI) derived to measure the response to organic pollution provided inconsistent results when applied to my streams. Nevertheless, gut content stoichiometry of the common mayfly grazer Deleatidium spp. indicated improvement in food quality (lower C:N ratio) with higher nitrate-nitrogen concentrations. These results indicated either nitrate-nitrogen does not alter invertebrate structural metrics across this nitrate-nitrogen gradient, or that these biotic metrics measure community structure aspects not affected by nitrate-nitrogen. I then investigated possible community composition patterns across the nitrate-nitrogen gradient. Unconstrained ordination (on presence/absence data) showed invertebrate communities at my sites were influenced primarily by discharge and shade, with the next most important driver being nitrate-nitrogen. A constrained ordination (on the same data) testing the singular effect of nitrate-nitrogen showed a marginally non-significant change in composition, with higher variability in community composition at higher nitrate-nitrogen concentrations. A further aim of my study was to test the draft nitrate-nitrogen bands proposed by Hickey (2013). These nitrate-nitrogen bands may advise guidelines to protect aquatic organisms as required by the National Policy Statement on Freshwater. Analysis of my invertebrate communities showed differences in composition, particularly at < 1 and > 6.9 mg/L bands. Several predatory caddisfly taxa: Triplectides, Neurochorema and Oeconesus were identified as potential indicator species of communities associated with low nitrate-nitrogen. These findings show that nitrate-nitrogen effects are difficult to detect, and that it is not the main driver of community composition in Canterbury streams. However, nitrate-nitrogen may be an important stressor for sensitive benthic invertebrate communities, as effects were observed on pollution tolerant organisms in this study. Therefore, this research has implications for freshwater ecologists and environmental managers striving to improve the health of streams on the Canterbury Plains.

Compared to natural forests, fast-growing plantations of exotic species such as Pinus radiata are often perceived as marginal habitat or unsuitable habitat for most native species. By studying Coleoptera (beetles) in a variety of landscape elements (pasture, native forest and different aged Pinus radiata stands) in a highly modified and fragmented landscape in New Zealand I aimed to determine the value of exotic plantation forests for native biodiversity, and how these species are affected by different sized clearfell harvest areas. Pitfall trap sampling of beetles showed that plantation forest stands can provide suitable complimentary habitat to native forest for many species. Rarefied species richness of Carabidae, Scarabaeidae and Scolytinae was not significantly different between habitats, however, habitat types differed significantly in their beetle community composition. Comparing different production habitats, Pinus radiata stands had a beetle community composition most similar to native forest. However, a small minority of species, e.g., Dichrochile maura, were restricted to native forest habitat highlighting the importance of retaining indigenous ecosystems within plantations. Unlike human modified habitats, native forests did not provide suitable habitat for exotic species. Clearfell harvesting is controversial and its impact on biodiversity is a key constraint for many forest certification programs, such as that administered by the Forest Stewardship Council (FSC). Despite this, no replicated manipulative experimental studies of the impact of different sized clearfell harvest areas on biodiversity have been undertaken at scales relevant to the New Zealand forest industry. One potential model of the impact of different clearfell harvest sizes is the concept of a threshold size. A threshold scenario may occur where clearfell harvest impacts increase at a rate disproportionate to the change in clearfell size over a small range of harvest areas, but impacts remain relatively unchanged either side of the threshold zone. I sampled Coleoptera in experimentally created 0.01, 0.05, 0.5, 5.0, 50 and 500 ha clearfells within Pinus radiata plantations in the central North Island of New Zealand. The wide range of clearfell harvest sizes, including some very small areas, such as 0.01 ha was instigated in an attempt to document potential clearfell harvest size thresholds. Rarefied native beetle species richness was higher in harvest areas compared to adjacent mature plantation stands. The beetle species richness in 5 ha and 500 ha harvest areas was significantly greater species than that in small 0.01 - 0.5 ha harvest areas. Although, the high beetle diversity recorded in 500 ha clearfells should be treated with caution due to confounding spatial autocorrelation. The degree of change in beetle community composition increased with increasing clearfell harvest area. Beetle assemblages in large harvest areas were less similar to their paired adjacent mature forest than smaller harvest areas. Although, constrained multivariate ordination techniques did show a short-term change in beetle species composition between recently clearfelled harvest areas of as little as 0.05 ha and adjacent mature P. radiata stands. The colonisation by open-habitat disturbance-adapted species was a key driver of this change, some species dispersed into clearfelled stands in significant densities within days post-harvest. Overall, there were no distinct short-term trends to the change in species richness as a function of increasing harvest area that would suggest an ecological impact threshold response. If short-term outcomes of clearfell harvesting are ameliorated by successful recolonisation, the long-term spatial arrangement of different aged stands becomes more important for the maintenance of biodiversity at the landscape level than short-term consequences of harvesting. By sampling selected beetle taxa in 1, 2, 4, 8, 16 and 26 year-old stands, I found that the abundance of seven out of eight of the species selected for analysis recovered to levels similar to those in adjacent mature forest within the timeframe of a single harvest rotation. Individual species utilised different aged stands, indicating different life-history strategies. For example, open-habitat, disturbance-adapted species such as Cicindela tuberculata and Sitona discoideus were prominent in young stands, and forest species such as Pycnomerus sophorae and Paracatops phyllobius were highly abundant in older stands. These alternative life-history strategies highlight the benefits of maintaining a mixture of different aged stands to increase biodiversity at the landscape level. This thesis fills an important gap in our knowledge of biodiversity in production landscapes. I show that plantation forests have value as complimentary habitat to native forest and they make an important contribution to the maintenance of biodiversity at the landscape level. Although clearfell harvesting is a severe disturbance to the forest ecosystem, the long-term recovery of beetle populations suggests that harvesting is not the key limiting factor to the enhancement of biodiversity in the plantation forests studied. This unusual situation is possibly the result of prior land-use history, as many plantations were established on degraded pastoral land, and harvest-sensitive species are unlikely to have survived this initial land-use change. As such, the severity of the long-term impacts of clearfell harvesting on biodiversity are likely to be context specific and will vary accordingly. The importance of spatial heterogeneity of habitat elements, including different aged plantation stands and native forest remnants, needs to be investigated in more detail to determine what limits biodiversity in this plantation landscape. Key points to consider are the proximity to, and proportion of, native forest cover in the landscape and the degree of connectivity among native remnants. It is these landscape-level attributes that may determine biodiversity at a regional scale, and more emphasis should be placed on landscape scale factors and there interaction with stand specific forest management practices. For example, the spatial mosaic of harvesting areas may need to be of a finer-scale when there are fewer native remnants within the landscape.

Natural enemies provide critical population regulation of many pest species, though their effects are not commonly incorporated into agricultural management decisions. Conservation biological control is an important tool that can be implemented to minimize pest damage, but applying it requires appropriate understanding of pest and natural enemy relationships. Through experimental cotton field trials, I identified predator: prey ratios based on key arthropod predators as action thresholds of the whitefly pest Bemisia tabaci MEAM1 (Dinsdale et al. 2010; equivalent to Bemisia argentifolii Bellows et al. 1994 [Hemiptera: Aleyrodidae]), validated their efficacy, and promoted them to cotton pest managers. This dissertation begins with a multi-year field trial where whitefly and natural enemy populations were manipulated with a series of insecticidal treatments to identify key arthropod predators. The critical abundance of four key predators necessary to suppress whiteflies was estimated through predator: prey ratios. These ratios were refined for commercial pest management and developed to conform to the current whitefly IPM framework as a simple to use management-decision tool that would be readily adopted and used by pest managers. Predator: prey ratios were then validated in 1) a second field trial, 2) commercial fields in Arizona and northern Mexico and 3) historical field trials conducted from 1997-2010, where whitefly management decisions made with the standard threshold and ratios, were compared with the standard threshold alone. I found no difference in management outcomes when decisions were made with the standard threshold alone, or with predator: prey ratios in the field trial, but analysis of potential decisions on commercial farms and with historical trial data indicated that the majority of sprays could be delayed if control decisions incorporated ratio-based thresholds. Finally, an outreach program was developed and deployed to present ratios as decision-making tools for cotton pest managers that reduce uncertainty in control decisions and optimize spray outcomes. Pest managers indicated positive changes in knowledge and a gradual adoption of ratios for decision-making. The implementation of whitefly control decisions that incorporate predator: prey ratios may reduce pest managers' uncertainty in decision-making, as well as insecticide use and management costs.