Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 74-75).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1956. / Typescript. Vita. Title from title screen (viewed May 9, 2006). Includes bibliographical references (leaves 93-100). Online version of the print original.

Thesis (M.A.)--Humboldt State University, 2006. / Includes bibliographical references (leaves 55-59). Also available via Humboldt Digital Scholar.

Four plant communities of southwestern British Columbia were studied in an attempt to answer the following related questions: (1) do communities of harsh physical environments exhibit any characteristic phytosociological features? (2) are there any correlations between environmental harshness and certain synecological properties of such communities ? (3) are species of such communities selected for reproductive specializations that tend to reduce their genetic variability? The four communities (representing three types of herbaceous or semi-shrubby vegetation) were a salt marsh, two coastal sphagnum bogs, and a subalpine meadow. In answer to the first two questions, the findings of this investigation indicate that: (a) species population structure becomes more aggregated as environmental heterogeneity and physical stress increase, and less aggregated as succession proceeds and interspecific competition increases. (b) interspecific association and correlation, both negative and positive, increase as environmental heterogeneity and competition increase. (c) levels of polyploidy within communities appear to be correlated with environmental rigor (broadly defined). (d) the most abundant species within a community are the most variable and presumably have the largest niches ; niche size and population variability decrease as interspecific competition increases. (e) within a community, ecological distinctiveness reduces interspecific competition; communities under the least stress (especially seasonal stress) have the most ecologically dissimilar1 species. (f) dominance decreases as species diversity increases, and species diversity is roughly correlated with overall environmental severity. In answer to the last question: (a) all four communities are dominated by predominantly outcrossing species; there is no major shift to self-pollination or apomixis in any of the communities. (b) an index of potential recombination was devised, embodying a number of aspects of reproductive biology, according to which there is no significant difference in potential recombination, on the average, between species of the four different communities. Plant communities and their constituent species both respond to evolutionary forces, but more or less independently, at different rates, and often in different or even opposite ways. Environmental stress has a powerful effect on the structure and function of plant communities, but in an evolutionary sense there is little difference between normal (mesic, zonal) environments and extreme or azonal environments to an individual species. Different selection pressures have been operating in salt marshes, sphagnum bogs, and subalpine meadows, but the present study indicates that, on the average, the resultant evolutionary strategies of the species of these communities are equivalent. / Science, Faculty of / Botany, Department of / Graduate

2v. : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (D.Sc.)--University of Adelaide, Dept. of Botany, 1975

Thesis (M.S.)--Oregon State University, 1984. / Typescript (photocopy). Includes bibliographical references (leaves 59-61). Also available on the World Wide Web.

Graduation date: 1991

The effects on vegetation of three small mammalian herbivores were determined experimentally in a subalpine meadow in southwestern Colorado. Pikas (Ochotona princeps) inhabit talus and forage on surrounding vegetation. Their foraging was consistent with predictions of central place foraging theory. Amount of foraging decreased with distance from talus, whereas selectivity increased. These patterns are expected to influence the resources used by pikas, and plant abundance and species richness increased with distance from talus, as predicted. Experimental exclusion of pikas demonstrated that a significant portion of the lower vegetational cover and species richness was due to pikas. A model postulating that the effects of pikas on vegetation resulted from a gradient in herbivory, and a corresponding gradient in the relative importance of herbivory and competition among plants, was generally supported. Total vegetational abundance and species richness increased in the absence of pikas. The increase in pika exclosures compared to controls was greatest near talus and decreased with distance. The initial effect of pika exclusion on cushion plants (assumed to be the poorest competitors among the plants in the absence of herbivory) was positive near talus, but was insignificant and tended to be negative at greater distance from talus. The prediction of eventual decline of cushion plant populations in the absence of pikas was supported in two of three sites after three years. The effects on vegetation of two co-occurring herbivores, pocket gophers (Thomomys talpoides) and voles (Microtus montanus), were evaluated using a factorial exclusion experiment. Non-independence of effects was assessed as presence of a significant interaction term in 2-way ANOVA. Gopher x vole interaction terms were at least marginally significant for many analyses. Results only weakly suggested direct foraging interactions between gophers and voles, but showed considerable importance of indirect, plant-plant interactions. Exclusion of either gophers or voles significantly increased vegetational abundance, however, no additional change in abundance resulted when both were excluded simultaneously. Exclusion of either increased forb abundance, and exclusion of gophers increased grass abundance. Only simultaneous exclusion of both, however, altered proportional abundances of plant groups.

Graduation date: 1984

Thesis (MS)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: David Roberts. Includes bibliographical references.