No description available.

Thesis (M.A.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph. D.)--Texas A & M University, 1997. / Includes bibliographical references (leaves 241-250).

No description available.

Oblique dunes have orientations that are intermediate between those of transverse and longitudinal dunes. The oblique dunes studied are reversing dunes which undergo no net annual migration when associated with normal meteorological patterns. From April 1980 through September 1980, the dunes migrated up to 65 feet (19.8 m) northwestward under the influence of prevailing onshore winds. High velocity northerly winds (November 1980 through February 1981), associated with the passage of winter frontal systems, caused the dunes to rapidly migrate 65 feet (19.8 m) southward. Volumes of sand transported by these strong winds were commonly reduced by accompanying rainfall. In October 1980 and March 1981 neither wind direction was dominant, and frequent changes in wind direction caused many of the dunes to become flattened. Hurricanes, which strike the area in late summer, have had no lasting effects on the dunes. Three major stratification types were observed in trenches and on etched surfaces. Translatent strata were deposited by wind ripples; grainfall deposits accumulated when saltating grains settled on leeward slopes of the dunes, and grainflow cross-strata were developed by avalanching on leeward slopes. Preservation of these stratification types occurred in zones of net deposition, predominantly leeward of the dune crests. Strata deposited during the summer wind regime dip northeast, whereas the winter strata dip in a southerly direction. The winter deposits are best preserved in the central cores of the dunes. This suggests that either the high velocity winds of the initial winter frontal systems destroy large volumes of the summer deposits, or that the dunes migrate southward, under the influence of dry northerly winds, during droughts. Oblique dune deposits should be difficult to discern in the rock record, because they may contain aspects of either transverse or longitudinal dunes. It is likely that some ancient oblique dunes have been mistakenly described as other dune types in the literature. / text

Every species has a limit to its geographic distribution. The problem is that we don’t really know why. Classical explanations propose that range limits occur where the ecological conditions overwhelm adaptation and populations are no longer self-sustaining. It is generally expected that population abundance and fitness decline towards range margins across a gradient of declining habitat quality. Current evolutionary and theoretical explanations of range limits predict that this geographic pattern of demography will result in genetic constraints in marginal populations, such that range expansion is thwarted by reduced evolutionary potential. In this thesis, I tested the key assumptions and predictions of range limit theory through an empirical evaluation of two coastal dune, endemic plants; Camissonia cheiranthifolia (Spreng.) Raim. (Onagraceae) and Abronia umbellata L. (Nyctaginaceae). In geographic wide surveys of a large proportion of populations across both species’ ranges, neither species exhibited declining abundance or performance towards its range limits. Central populations of C. cheiranthifolia tended to have a higher production of seeds per unit area than marginal populations. Although this pattern demonstrated the potential for gene flow from central sites to swamp selection in marginal sites, results from a transplant experiment suggested that this was unlikely. Experimental populations of C. cheiranthifolia originating from ≥ 675 km south of the northern range limit exhibited similar levels of fitness when planted at the range margin. Along a 200 km transect across the limit, and in contrast to expectations, fitness of all populations increased towards the limit and generally remained high beyond the limit. Individuals from all populations reproduced and matured fruit beyond the limit, suggesting that if individuals dispersed beyond the limit that populations would establish. The species’ abrupt distributional limit also did not correspond to an abrupt shift in ecological conditions, despite the association of fitness with plant community and microhabitat variables. Overall, ecological tolerances to fitness or niche-based explanations to range limits do not adequately describe the distributions of either species. Constraints on dispersal rate, the influence of anthropogenic factors on habitat dispersion and limited genetic variability for fitness related traits are addressed. / Thesis (Ph.D, Biology) -- Queen's University, 2007-05-13 16:45:44.456

No description available.

Bibliography: v. 1, leaves 127-152 / 2 v. : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics, 1986

Thesis (Ph.D.)--McMaster University (Canada), 1991. / Source: Dissertation Abstracts International, Volume: 54-02, Section: B, page: 0699.