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Without an adequate understanding of complex interactions between native and non-native species, management of invasive species can result in unforeseen detrimental impacts. I used both field and laboratory experiments to study reciprocal species interactions between the endangered Mohave tui chub (Siphateles bicolor mohavensis) and invasive western mosquitofish (Gambusia affinis). I also examined the impacts of both fish species on the aquatic invertebrate communities in desert springs. I demonstrate a case of intraguild predation (IGP) as a mechanism facilitating co-persistence of the endangered Mohave tui chub with invasive mosquitofish using field mesocosm experiments. In this case of IGP, adult tui chub prey on adult and juvenile mosquitofish, while adult mosquitofish prey on tui chub eggs and/or larvae. I conducted laboratory predation trials to assess if IGP was size-structured due to predator gape-limitation. I explored sex specific differences in gape-size limitation in mosquitofish, because mosquitofish are sexually dimorphic. Larval tui chubs had lower survival in the presence of female mosquitofish than in the presence of males. Reciprocally, male mosquitofish had lower survival than the females in the presence of Mohave tui chub. These results combined with vulnerability modeling supported that IGP in this system is size structured based on gape-size limitation. These results collectively suggest size-structured IGP may facilitate the co-persistence of these two fish species. My findings also suggest that mosquitofish may not be a limiting factor for the persistence of the endangered Mohave tui chub. Further, habitats currently harboring mosquitofish were considered as future refuge habitats for Mohave tui chub, a management option previously un-available. In addition to such reciprocal interactions between fish species, recently established fish populations may impact unique invertebrate communities. Mesocosm experiments with sympatric and allopatric populations of tui chub and mosquitofish showed negative impacts of both fish species on changes of invertebrate community structure. Specifically, fish caused population declines and, in some cases, extirpations of various invertebrate taxa. These results suggest important conservation implications of invasive fish as well as protected fish transplants into fishless desert springs. Overall my research emphasizes the complexity of ecological interactions between native and non-native fish species in desert aquatic systems.

Durch Messungen von spektraler optischer Dicke, Sonnenaureole und Himmelshelligkeit in Kombination mit den Programmen CIRATRA und BILANZ werden die optischen Eigenschaften von Sahara-Wüstenaerosol und dessen klimatische Wirkung unter Berücksichtigung der Nichtsphärizität der Aerosolpartikel untersucht. / By combining measurements of spectral optical thickness, solar aureole and sky brightness with the programs CIRATRA and BILANZ the optical porperties of Saharan desert aerosol and its climatic effects are investigated, including a consideration of the Nonsphericity of the aerosol particles.

The nitrogen budgets of Eurotia lanata (Pursh.) Moq. and Atriplex confertifolia (Torr. and Frem.) S. Wats salt desert shrub plant communities were investigated. In each, a complete biomass and organic nitrogen inventory was made. In addition, investigations of the nitrogen fixation potential of soil surface microflora and inorganic soil nitrogen relationships were carried out. Greater total biomass and organic nitrogen was found in the above-ground portions, annual shoot productivity, and litter of the Atriplex community. However, the Atriplex community was exceeded by the Eurotia community in root biomass. Roots accounted for 74 and 87 percent of the plant biomass and 83 and 90 percent of the associated organic nitrogen in Eurotia and Atriplex communities respectively. Root biomass distribution at various depths was markedly different in the two communities. Differences between communities in relative amounts of various plant parts and litter are related to contrasting plant growth habit, and differences in soil texture and soil salinity. Total plant biomass estimates, which were 18,480 and 17,300 kilograms per hectare for Eurotia and Atriplex communities, were not significantly different and reflect the overriding influence of macroclimate and associated moisture limitation. Under laboratory conditions the soil surface microflora of the Atriplex community was able to fix significant amounts of atmospheric nitrogen while that of the Eurotia community did not. Nitrogen fixation potential in the Atriplex community was associated with the presence of abundant lichen cover and associated heterocvstcontaining blue-green algae of lichen interspaces. Differences between communities were found in rates of mineralization, downward flux, and pattern of utilization of inorganic soil nitrogen. Soil salinity appeared to strongly limit inorganic soil nitrogen mineralization as well as root growth and nitrogen uptake in the lower part of the Atriplex soil profile; however, this lack of biological activity was compensated for by a greater downward flux of inorganic soil nitrogen from decomposing litter and surface soil in the Atriplex community. Shoot and root litter appears to be the most readily available source of inorganic soil nitrogen for plant growth in salt desert shrub plant communities.

The sand dunes lying ten miles northwest of Kanab in Kane County, Utah, support a sparse plant cover with four species dominating the vegetation: Psoralea stenostachys, Sophora stenophylla, Oryzopsis hymenoides, and Wyethia scabra var. attenuata. Of these Psoralea and Wyethia are endemic to the dunes or to a limited area which includes the dunes. The pineer species gain a start in the valleys between dunes and occupy the area only until sand covers them or until sand is blown away from their roots. Stabilization of the soils is not permanently in the interdune valleys and the dunes continue to wander. The low fertility of the soils, the low moisture content, the extremes of temperature, light, and other environmental factors limits the number of individual plants which can occupy the dunes. The region will continue to have actively moving dunes until major climatic changes occur permittimg a denser plant cover which would tend to stabilize the sands.

This problem was a study of plant species in the Escalante Desert, Utah, in relation to soil conditions. The plants were surveyed by the transect-plot method. The plants and soils were analyzed by percentage-frequency techniques. There is no measurable correlation between soil series and the dominant plants which occur on the soils. There is no correlation between soil types and the plants that are dominant on the soil types. There is a definite correlation between textural classes of the soil and the plants that are dominant on these classes.

With the evolving geopolitical situation and Sweden´s recent NATO integration, the understanding of Host nation supports multifaceted role is increasingly vital. Previous research lacks a theory regarding host nation support. The purpose of this thesis is to seek a better understanding on host nation support and to initiate a theoretical framework on the subject. By employing a method of hypothetical deductive approach, the study analyzes identified factors such as deterrence, planning, transit, infrastructure, and civil support. The factors were identified from previous research and motivated with theories from military science and the authors reasoning. The theoretical framework has it´s grounds in the authors reasoning that deterrence is the purpose of host nation support and the other factors are contributory to it. The analysis centers on the cases Operation Desert Shield and Operation Desert Storm during the Gulf war. The result confirms various of the factors contribution to the deterrence in host nation support in the specific cases and that there are complementary factors involved also.

The Desert Solitaire curriculum was designed as a basis for exploring Edward Abbey's book, of the same name, in a high school field ecology class. Students read the book over a period of six weeks during the middle of the school year. Lessons were designed to aid students in exploring their home ecosystem, the Mojave Desert, via comparison with Arches National Monument as described in Desert Solitaire. This exploration fosters in students a sense of place and connection with their home environment. With little alteration, the curriculum can be used by students to examine their own ecosystem, even if it is not a desert. Furthermore, this curriculum can be used for delving into environmental issues, exploring environmental values and/or beliefs, or as an introduction to the genre of nature literature.

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Doctor of Philosophy / Department of Geography / Richard A. Marston / David R. Seamon / Sprawling over 180 square miles of California’s Mojave Desert, Wonder Valley was founded in the early 1950s and today is an unincorporated community of approximately 1,000 residents. The community’s landscape is expansive and unsettling, featuring a chaotic assortment of residences that include abandoned homesteads, squatter settlements, artists’ studios, middle-class cabins, and luxury vacation properties. This dissertation explores Wonder Valley’s enigmatic place identity from residents’ point of view, drawing on an experiential understanding of place grounded in humanistic and phenomenological geography. Specifically, the dissertation makes use of Edward Relph’s explication of place identity to guide empirical inquiry and conceptual structure. Drawing on resident interviews, place observations, and textual analysis, the dissertation identifies and explicates three distinct Wonder Valley identities—homesteaders, dystopics, and utopics. Arriving in the 1950s, homesteaders were Wonder Valley’s first inhabitants and express a practical connection to the landscape that is interpreted in terms of environmental reach, specifically, the creation, maintenance, and extension of environmental and place order. During the 1970s, as many homesteaders abandoned Wonder Valley, dystopics arrived and today include two subgroups: first, a criminal element pulled to Wonder Valley because of its local isolation but regional proximity to Los Angeles; and, second, destitute squatters pushed out from other communities and having nowhere else to go. The third group identified is utopics, primarily artists from Los Angeles and San Francisco, who arrived in the early 1990s, attracted by Wonder Valley’s natural beauty and sacred ambience. The dissertation explores how these three groups arrived at different times, for different reasons, to create vastly different landscapes, to engage in opposing aims and activities, and to understand Wonder Valley’s meaning as a place in greatly contrasting ways. These differences in meaning are most directly expressed in the common areas of public land, which have often become sites of inter-group tension and conflict, particularly in regard to abandoned homesteads and the use of off-road vehicles. To interpret this group conflict conceptually, the dissertation develops what is termed existential ecotone— a unique mode of place experience generated by overlapping but contrasting modes of being-in-place.