Thesis (Ph.D.)--University of Wyoming, 2007. / Title from PDF title page (viewed on July 26, 2010). Includes bibliographical references (p. 186-203).

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 167-179).

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Why do animals make false alarms; are false alarms truly deceptive; and if, just as in Aesop's fable 'The boy who cried wolf' , animals can learn to ignore false alarms, why doesn't deception break down? I investigated these questions in a population of habituated and individually recognisable fork-tailed drongos (Dicrurus adsimdis), in the South African Kalahari Desert. Drongos either self-foraged, when they hawked and gleaned small insects, or followed other species stealing large terrestrial prey that hosts excavated. Stealing food from other species enabled drongos to capture prey otherwise unavailable to them and accounted for over 20% of their biomass intake. This was of greatest benefit during the morning and on colder days when payoffs from stealing remained stable while those from self-foraging declined (Chapter 3). Drongos stole food using two strategies, either by physical attack or by producing false alarm calls in response to which hosts fled to cover, enabling drongos to fly down and collect abandoned food. False alarms increased overall success, and were produced when stealing small food items unprofitable to gain by physical attack, or when stealing from larger species more likely to defend food (Chapter 4). Drongos produced both their own alarm calls and mimicked alarm calls of other species in their false alarm repertoire. Playback experiments on two host species, pied babblers (Turdoides bicolor) and meerkats (Suricata suricatta), confirmed that these false alarm calls were deceptive because they were as effective at alerting hosts as true alarms given to approaching predators (Chapter 5). Further playbacks showed that hosts were more likely to be deceived by mimicked false alarm calls, including mimicry of the host species alarms, than by a drongo' s own alarms. In addition, host species habituated to repeated playback of the same alarm but resumed their response when a new alarm call was played, and drongos naturally changed their alarm calls when hosts failed to respond to a previous false alarm. Therefore, by employing vocal mimicry to vary their alarm calls drongos were both more likely to deceive hosts, and to maintain deception. Consequently drongos evaded the frequency dependent constraints which typically limit payoffs from deception when species produce only one signal (Chapter 6). The drongos sophisticated communication strategy raises questions for future research regarding the mechanisms leading to the production of complex behaviour.

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The idea of taming the Desert Southwest has captivated the American psyche for hundreds of years. The intoxicating beauty of the wide-open and wild landscape has lured people westward. The lure remains: the U.S. census figures are forecasting that by the year 2030, more than 67 million people will live in the West and that Nevada, Arizona, and Utah will be among the top 5 states in the nation in terms of percentage of population increase. The survival of the Desert Southwest's ecosystem depends greatly on the geographic distribution of this growing population. As the Desert Southwest's population continues to grow, a new urban paradigm is needed. Americans’ 20th century desire to live in nature in order to escape the squalor of the city has been fueled by the automobile and highway systems. These conditions have defined a sprawling and suburbanized pattern of settlement throughout the United States. Charles Waldheim says, “Across many disciplines, and for many centuries, the city and the country have been called upon to define each other through a binary opposition.” Resulting urban models sought to dissolve this opposition between city and nature. Such development had enormous horizontal spatial implications. But, as Edward Glaeser puts it, “it would be a lot better for the planet if their urbanized populations lived in dense cities built around the elevator, rather than in sprawling areas built around the car.” Our horizontal development has had devastating effects on the ecosystems they encroach upon and swallow up. One landscape that is particularly threatened by our outward sprawl is the Sonoran Desert located in the Southwestern United States. The beauty of the wild and unique desert landscape has drawn people and development to it for centuries. The dilemma is that the closer we get, and the more that we try to live within this natural world, the more we destroy it. The suburban development in the region has had a disregard for water usage and resources. Diverted waters from the West’s great rivers, rising temperatures, highways, and loss of habitat have made an arid climate even more unforgiving, put desert flora and fauna in danger of extinction, and endangered the landscape that has been our muse for hundreds of years. This thesis aims to define an intimate relationship between city and nature in the Desert Southwest, but unlike its historical counterparts, proposes that we build up instead of out in order to reduce water and energy use, contain expansion and growth, and begin to repair the land that we have loved to death. / 0 / SPK / specialcollections@tulane.edu

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Observations by local people in the Mier area, southern Kalahari, South Africa, indicated that degraded rangeland does not recover within a time frame acceptable to landowners. Pristine vegetation in this linear dune system consists largely of a herbaceous layer dominated by perennial grasses. Woody vegetation is sparse on dunes and interdunes in good condition. The dunes and interdunes react differently to disturbance, probably because of differences in substrate stability, soil particle size distribution and consequent differences in soil nutrient distribution and moisture content. Degraded dunes are devoid of any vegetation, except for Stipagrostis amabilis, a rhizomatous grass which remain in small clumps, and the tree Acacia haematoxylon. The latter increases in numbers probably due to the high moisture content in degraded dunes. Moisture content in degraded dunes remain high even during prolonged dry periods. Interdunes are more susceptible to degradation and are invaded by the long-lived shrub Rhigozum trichotomum and the annual grass Schmidtia kalahariensis. Both these species compete with perennial grasses for moisture. Additionally, depleted seed banks and increased seed predation by ants (Messor capensis) may also affect the re-establishment of perennial grasses in the interdunes. The main conclusion from this study is that degraded southern Kalahari rangeland cannot recover spontaneously at the landscape scale because of a negative feedback mechanism that prevents establishment and growth of seedlings. The hypothesis put forward is that rangeland ceases to react to rainfall as an ecosystem driver as it becomes degraded. Once degraded, wind controls the dynamics of the system and recovery, irrespective of rainfall, is almost impossible. In contrast, detailed studies at the level of small isolated populations of S. amabilis and S. ciliata on degraded dunes indicate high rates of population growth. The scales at which these processes exist are contradictory and may not be contradicting. Rangeland managers should take cognisance of the influence of the spatial and temporal scale at which they operate, and on which they base their decisions. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2000.

Mickey Springs in the Alvord Desert, southeast Oregon, is analogous to other Basin and Range hydrothermal systems where the requisite conditions of heat source and permeable pathways are met through crustal thinning due to normal faulting. This study examines the morphology and lifespan of near-surface spring features through use of ground penetrating radar, thermoluminescence (TL) dating, and elevation modeling. Duration of hydrothermal activity at Mickey Springs has not previously been determined, and age determinations of sinter at the site are conflicting. The reason for and timing of this change in silica saturation in the hydrothermal fluid has not been resolved. Three morphologies of silica sinter deposition have been identified at Mickey Springs. These are (1) well-sorted, fine-grained sandstone with ripple marks, cross beds and preserved root casts, to poorly-sorted conglomerate of primarily basalt clasts, both cemented by coeval silica deposition, (2) large depressions (12-32 m diameter) rimmed with sinter, characterized by fine silt and clay blanketing a sinter apron and infilling the central depression, and (3) quaquaversal sinter mounds identified by outcropping pool-edge sinter typically surrounding a shallow depression of loose sediment. Silica-cemented sandstone and conglomerate were the first features formed by coeval hydrothermal processes at the site, and were emplaced prior to 30 kya as suggested by structural and stratigraphic relationships. Structure between two interacting fault tips may have constrained the extent of silica cementation. By 30 kya, a left-stepping fault oriented roughly north/south further constrained the near-surface permeable zone. TL dates from sediment stratigraphically below and above sinter aprons around mounds and depressions (former spring vents) indicate sinter deposition between 30 and 20 kya. Location of these features was dictated by development of the left-stepping fault. As pluvial Lake Alvord filled at the end of the Pleistocene, lake sediment filled most vents, which were largely inactive, with fine-grained silt and clay. Today, hydrothermal activity persists in two modes: (1) The current high-temperature springs, steam vents and mudpots concentrated in a 50 x 50 m area south of the sinter mounds and depressions, and (2) scattered springs and steam vents that exploit previous permeable pathways that once provided the hydrothermal fluid which precipitated the sinter aprons. Currently there is no active silica sinter deposition at Mickey Springs. Structures and stratigraphic relationships identified through this study favor a transport-limited and structurally controlled model of fluid transport. Sinter deposition is determined to have occurred before the most recent highstand of pluvial Lake Alvord. A climate driven model, where groundwater recharge from pluvial Lake Alvord circulates to a deep heat source and enhances spring discharge, is not supported by these findings, as no evidence was found for sinter precipitation after the drying of the lake. Future studies of other hydrothermal systems in the Basin and Range may reveal that permeable pathways along local structures are the primary drivers in this region.