Positive frequency-dependent predation (FDP) has been proposed as a species coexistence mechanism and theoretical models have shown how it may function. In positive FDP a rare species receives a temporary reprieve from predation pressure allowing an increase to its population growth rate and a chance for it to recover from rarity. This study tests for frequency-dependent foraging by granivorous desert rodents on the seeds of three species of winter annual plants that grow in the Sonoran Desert. While the preference for one species is much higher than the other two, preferences for each species are higher when common than when rare showing an asymmetric form of positive FDP. This study is the first empirical test for positive FDP on winter annual plants and by granivorous desert rodents and one of few to use more than two prey species, native prey species, or asymmetrically preferred prey species.

A major challenge in plant ecology is in understanding how species strategies mediate interactions between the environment and fitness. Variation in niche strategies that affect phenological, physiological, and reproductive traits will allow species to partition resources differently in space and time, allowing for coexistence of many species and strategies within a community. How species differentially respond to variable environments will ultimately influence their population dynamics and geographic distribution. This dissertation approaches this topic from two perspectives: (a) examining the interaction between biogeography and variable demographic strategies in desert annual plants, and (b) examining the costs and benefits of contrasting reproductive strategies in co-occurring selfing and outcrossing desert annuals. Firstly, I tested the abundant center model to determine the role of range position on plant population dynamics. I examined how the geographic and climatic position of 13 desert annuals found at a common location, the Desert Laboratory at Tumamoc Hill in Tucson, Arizona, related to their demography over a 25-year time span. I found that species for which the Desert Laboratory was close to the center of their geographic range have less variable long-term survival and fecundity compared to species for which the Desert Laboratory was further from the center of their range. Secondly, I studied how related species with contrasting mating systems respond to variable environments to affect plant performance. In a three-year field study I investigated how inter-annual variation in plant reproductive phenology affects synchrony with pollinators and herbivores. Since selfing species are guaranteed to reproduce in the absence of pollinators, seasonal and annual variation in phenology resulted in less variable plant reproductive success compared to outcrossing species. Greater variation in reproduction in outcrossing species resulted from asynchrony in some years between plants and pollinators. In a greenhouse study examining the interaction between mating system and drought, I found that the physiological functioning and survival of outcrossing species was more strongly negatively affected by drought conditions, suggesting that selfing species have an advantage in more arid environments. These studies demonstrate how plant reproductive and physiological strategies can play a critical role in influencing fitness, population dynamics and geographic distribution.

Prior to this study, knowledge of Gobi Desert prehistory was mostly limited to early and mid-20th century descriptions of undated stone tool assemblages from unanalyzed museum collections. This research focuses on the use of extensive existing museum collections to establish a baseline chronology of technology, economy, and land-use for prehistoric Gobi Desert groups. Radiocarbon and luminescence dating are used to establish an artefact-based chronology and provide a relative age for 96 archaeological site assemblages. Interpretations of land-use derived from lithic analysis are compared to detailed regional and local palaeoenvironmental records in order to contextualize residential mobility and subsistence. Results indicate that a dramatic shift in land-use after about 8000 years ago was related to a combination of widespread forestation and the increased productivity of lowland habitats during a period of high effective moisture. Hunter-gatherers organized their movements around dune-field/wetland environments, but utilized a range of both high- and low-ranked foods such as large ungulates from adjoining plains and uplands, and seeds and/or tubers from dune-fields and wetlands. New radiocarbon dates indicate that the use of dune-fields and wetlands persisted into the early Bronze Age, overlapping with the rise of nomadic pastoralism across Northeast Asia. These findings illuminate the period just prior to the rise of nomadic pastoralism in Northeast Asia and add considerable depth to our understanding of hunter-gatherer adaptations within arid environments following the Last Glacial Maximum.

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This dissertation examines the bacterial diversity of hyperarid and arid regions of the Atacama Desert, Chile, as a first step towards understanding the global biogeochemical significance of arid-land microbial communities. The specific objectives were to characterize bacterial diversity and infer the possible metabolic potential of these bacterial communities, and to evaluate the influence of moisture exposure on community structure. In addition, the strengths and limitations of available tools for probing microbial diversity and activity in terrestrial ecosystems were characterized for their application to extreme oligotrophic communities. Preliminary PCR-DGGE analysis of a west-east elevational transect from the Pacific Ocean near Antofagasta to the western slopes of the central Andes indicated that bacterial communities along this transect belonged to two distinct community types: 1) hyperarid (700 - 2000 m) and 2) arid (2500 - 4500 m) communities that included both vegetated and unvegetated regions. Subsequent diversity analysis of these two regions revealed novel but distinct communities in both regions. A greater diversity was observed in the unvegetated arid regions than in the unvegetated hyperarid areas. The unvegetated arid sites were characterized by a bacterial community harboring a combination of radiotolerant and halotolerant heterotrophs as wells as diverse phylotypes closely related to chemolithoautotrophs. These rare phylotypes may be uniquely adapted to arid ecosystems. Molecular tools evaluated for community diversity analysis included PCR-DGGE, Sanger-clone and 454-pyrosequencing analysis of 16S rRNA gene libraries, and the use of reverse transcriptase quantitative PCR (RT-qPCR) for quantifying the impact of environmental variables on the metabolic activity of a specific organism. These techniques were evaluated using the ecosystems of the Atacama Desert as well as model ecosystems designed to address specific questions. Molecular tools are invaluable to the study of microbial ecology because they facilitate the study of fastidious organisms that are difficult or impossible to culture, but the analysis presented in this dissertation demonstrates that each of these methods has limitations and biases which must be acknowledged to avoid inaccurate conclusions from skewed results. The most complete picture of the taxonomic and functional profile of a microbial community is obtained by employing a combination of molecular techniques.

The North American Monsoon System (NAMS) is a significant weather and climate phenomenon that brings critical rainfall to the southwestern United States and northwestern Mexico. As a result of the North American Monsoon Experiment, and research efforts surrounding the field campaign, the understanding of the NAMS has increased considerably over the last 15 years. In addition questions concerning potential flash flood causing mechanisms of the NAMS have not been thoroughly investigated. This dissertation is comprised of two papers that collectively address the aspects of the literary understanding of the NAMS as we know it today and conduct an investigation into the complex interactions between various weather systems that may influence the NAMS. In the first paper, a review of the major research of the NAMS literature since the last comprehensive review 15 years ago is conducted. The results of his review are assessed for where our understanding has been improved and where future research needs to be guided for purposes of the second paper. Based upon the results from the literature review, the second paper focuses on identification of inverted troughs and gulf surges based upon lower- and mid-level atmospheric parameters for purposes of assessing the impacts on National Weather Service Storm Report flash flood dates. This research contributes to the synthesis of the current knowledge of the NAMS in general and to the specific regional impacts that do occur during periods of heavy precipitation over the NAMS region for purposes of improving meteorological predictability of flash flooding. The results can (1) gauge our understanding of the NAMS literature to date and (2) improve meteorological forecasts through the recognition of synoptic and sub-synoptic patterns related to the NAMS that are most likely to cause flash floods.

Demographic, biological and behavioural knowledge, together with information on the ecological interactions and impact of a species is fundamental to effective management of most mammal species. In this study, these aspects were investigated for a population of feral horses in the Namib Naukluft Park of Namibia, which lies within a part of the Namib Desert. An attempt was made to evaluate the justification of the continued existence of this exotic species in a conservation area, as well as to provide baseline information and recommendations regarding management of these horses. The study investigated the botanical component and grazing capacity of the area inhabited by the horses, as well as the demography and quality of life of the horses. The study further examined the possible negative impact the horses may have on the natural biodiversity of the area. Finally, it looked at the historic, scientific, aesthetic and economic values of the horses. The collected data was then used as a technical basis for the development of a draft management plan during a stakeholder workshop. The study proposed a range of grazing capacity values related to the total rainfall of the preceding twelve months, based on grass production in response to rainfall in different plant communities. The horses, as well as the native large herbivores, utilized the study area according to the patchy rainfall patterns typically found in the Namib Desert. The population size of the horses fluctuated between 89 and 149 over a ten year period. The social structure of the population was more significantly influenced by artificial interference than natural disasters which had implications on natality, mortality and genetic viability. Termite activity, measured as utilization of grass provided in bait boxes, did not correlate with horse density and seems, instead, to be influenced by soil properties. The results of ant and tenebrionid beetle species composition surveys and analyses did not indicate a significant negative impact from the horses on the study area. No indication could be found that the horses threaten the survival of any native species in the area or that they change the vegetation structure. It appears as if the biodiversity of the area is subjected to large natural stresses due to the continued and frequent desiccation in the desert environment. The impact of the horses is therefore probably minor to that of the climatic stochasticity. It also became apparent that the horses have developed significant historical, scientific and tourism value. The general public opinion is that the horses should be managed as a wild population with minimal artificial interference. / Thesis (Ph.D. (Zoology))--North-West University, Potchefstroom Campus, 2006.

Pastoralism on the Mongolian steppe encompasses limited physical resources and evolving anthropogenic influences. Little-studied, the Inner Asian region encounters changing climates, evolving land use practices, and socio-economic transition that impact the natural and human geography. This thesis investigates how bio-physical factors and herder action determine the pastoral environment in the Gobi Desert, Mongolia. Research, focusing on drought, degradation and the extreme winter conditions that define pastoralism in Mongolia, examines pastoralists' perception of and interaction with their environment. This approach highlights steppe ecological and social processes within the global dryland debate. Fieldwork in Omnogovi and Ovorhangai Province established that drought is endemic in the region. However, drought events were independent of extreme winter conditions and did not exacerbate their impact. Degradation was not found at water points as vegetation cover decreased with distance from water. While remote sensing showed a decline in vegetation cover over time, it did not establish desertification on the steppe. Changing physical, socio-economic, and political conditions since 1990 continue to impact Mongolian pastoralism. Environmental conditions, particularly water resources and pasture quality, were paramount herder concerns. This research showed that pastoralists are economically motivated, differentiate on multiple dimensions, and value communal land stewardship. On the steppe, traditional mobile livestock practices improve livelihoods and remain an effective management approach. However, the future of pastoralism is uncertain as herders settle, the population ages, and children become educated. Thesis results emphasize the interaction of physical and social environments will define pastoralism's role in the Gobi Desert

General objectives of my study were to describe the reproductive ecology of gray gulls in the large Lealtad colony, with emphasis on demographic parameters and physiological adaptations of eggs and chicks, which would complete some original objectives established in the early 1980's by Guerra and Fitzpatrick. Specifically, my study focused on describing, then comparing with other desert and non-desert nesting larids, interactive effects of ambient physical conditions and nest-site predation on eggs and chicks.

8 THE FOOD DESERTS ISSUE - THE CASE STUDY OF ZLÍN ABSTRACT This thesis attempts to provide an introduction to the 'food deserts' theme by outlining how the problem of access to food for households has become an increasingly important issue in the transforming Czech retail market. The first part reviews the development of new types of retail space in the Czech Republic in the past two decades. The emphasis is principally on the growth of new formats of food retailing - supermarkets, hypermarkets and discount stores - which to a greater or lesser extent have affected every local market and supported spatial restructuring of the Czech retailing. On the other hand, it has also changed the pattern of traditional shopping facilities, which in turn have often experienced decline. The second part of this work describes the retail change in Zlín and analyses the local distribution of food retail stores. It takes both quantitative and qualitative approach to define areas with relatively poor access to adequate food provision. There, it particularly focuses on consumers with lower mobility who are thus more restricted in their grocery choice. The last section includes conclusions, mainly the discussion of resulting policy responses, possibilities of prevention of this phenomenon, as well as implications for...