Thesis (M.S.)--University of Wisconsin--Madison, 1980. / Typescript. eContent provider-neutral record in process. Description based on print version record.

Proefschrift--Leyden. / "Samenvatting" in Dutch.

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Permafrost disturbances, including active layer detachments (ALDs), have occurred both recently and historically at Cape Bounty, Melville Island. These recent and relict ALDs were studied to determine their short- and long-term landscape effects. Six relict detachments showed altered vegetation and site characteristics, despite 60 or more years of recovery. Of the environmental variables studied, including soil moisture, soil temperature, and active layer depth, soil moisture showed the greatest changes in disturbed zones. These were attributed to the concavity of disturbance, which allows for more snow accumulation. Two vegetation types influenced by moisture regimes, polar desert and mesic heath, were compared to determine the role of moisture in recovery. The best indicators of disturbance differed in areas of different moisture regimes, with canopy height showing increases in disturbed mesic heath zones, while Normalized Difference Vegetation Index (NDVI) values increased in polar desert disturbances. Ultimately, the comparison of vegetation in disturbed and undisturbed zones revealed differences to be highly localized and minimal. Remote sensing was utilized to compare the effects of recent and relict disturbances as seen on satellite and airborne imagery. Vegetation was classified using NDVI, and zonal separation of these values in ALDs revealed the upper scar areas and lower toe zones contained significantly different NDVI values. The upper scar values were similar to undisturbed control areas, as blocks of vegetation in these areas often contain unmodified vegetation, which later helps with revegetation. The lower toe zone displayed both elevated and lower NDVI values, as material accumulates in these areas but often in a complex with bare soil. Remote sensing techniques also allowed for site characterization of disturbances, with physiographic factors including slope and flow properties determined through satellite imagery. Slope values ranged from 3 to 13 degrees in each disturbance, but were found to be slightly lower in relict disturbances, as recovery and revegetation have reduced these slopes. Flow paths were identified in ALDs, however similar patterns were also identified in surrounding undisturbed landscapes. Given the small scale of many ALDs, it is difficult to characterize the nature of the changes associated with these events, particularly for relict ALDs. / Thesis (Master, Geography) -- Queen's University, 2011-07-28 11:42:47.636

No description available.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Aster section Eucephalus (Nutt.) Munz & Keck is comprised of about 16 taxa in North America (some rare and localized, others abundant and widespread) which appear to form a homogeneous, and probably monophyletic, group. I used a stratified sampling design to select 141 specimens from 1,669 loaned herbarium sheets. I chose morphological characters for analysis on the basis of character descriptions and the taxonomic history of Aster section Eucephalus species derived from published scientific papers and floras. I calculated similarity indexes based on 33 to 36 characters, using Gower’s general similarity coefficient. Thirty-one phenetic groups were found by clustering specimens with UPGMA. The cluster memberships were adjusted by evaluating changes in the eigen values generated during discriminant analysis of “before” and “after” cluster memberships. An axis with increased value indicated that discrimination between the groups had increased relative to the axis, and a decrease showed that the groups were less separated relative to the axis. Those characters that could not be used in discriminant analyses were assessed for gaps or overlaps among groups by applying t-tests and visual inspection of box plots. Twenty-five phenetic groups remained after the iterative adjustment process. Taxonomic names were assigned to the phenetic groups based on published descriptions. Aster eastwoodiae Zaml. comb. nov. (Aster bicolor was not an available name for this taxon) reinstates a morphologically distinct taxon (Eucephalus bicolor Eastwood), previously included in A. brickellioides (Greene) Greene, that is endemic to the Klamath region of Oregon and California. Aster engelmannii Gray is divided into var. engelmannii and var. monticola Zaml. var. nov. based on size, number of phyllary rows on the involucre, and trichome characteristics. Aster wasatchensis (Jones) Blake is separated into var. wasatchensis and var. grandifolius Zaml. var. nov. based on plant size, phyllary colours, and leaf trichome characteristics. Phenetic groups were used as the bases for cladistic analyses and a hypothesis of descent was developed from a cladogram derived by coding taxon character means as multi-state characters. Ancestral conditions were inferred from multiple outgroups including Aster turbinellus Lindel. ex. Hook. Aster wasatchensis was hypothesised to be the basal species. Locality information gathered from herbarium labels was used to produce distribution maps. Biogeographic distribution information combined with cladistic results, and an assumption of a founding taxon from Mexico (Noyes and Rieseberg (1999) hypothesised that New World asters were derived from southern taxa) suggested several biogeographical hypotheses for Aster section Eucephalus. Four lines of descent were hypothesised to give rise to I) an ancestral form in the Sierra Nevada; 2) an ancestral form in the Siskiyou Mountains of Oregon, together with Aster giaucodes Blake in the Great Basin and the Rocky Mountains; 3) a widespread group including Aster engelmannii Gray, A. vialis (Bradshaw) Blake, A. perelegans Nels. & Macbr., and A. glaucescens (Gray) Blake; and 4) A. wasatchensis (Jones) Blake in Utah. Taxa could then have developed through the processes of range expansion, isolation and vicariance. Aster wasatchensis is probably a palaeoendemic, whereas A. eastwoodiae, A. gormanii (Piper) Blake, A. vialis, A. glaucescens, and A. paucicapitatus (Robins.) Robins, are probably neoendemics. The current distribution of taxa likely reflects range modifications resulting from climatic changes caused by glaciation, and probably does not indicate the original relative positions of the taxa. Oregon and northern California form one area of species richness and Utah forms another. For these taxa, the coastal ranges exhibit more diversity and a higher rate of endemism. Rarity in Aster section Eucephalus is probably due to limited habitats and recent origin rather than any particular character trait. / Graduate

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 312-321).

New Zealand is a continental island surrounded by deep-ocean, with a complex system of currents and oceanographic anomalies that may serve to isolate populations of coastal marine organisms. In particular Cook Strait is a 26 km wide body of water separating the North and South Islands which is characterised by complex interactions of tides and converging water masses. Cook Strait is a geologically recent formation that may also impart an historical influence on the biogeographic distribution of coastal marine taxa. In order to investigate the phylogeographic structure of coastal marine taxa around New Zealand's coastline and to investigate the processes that may contribute toward this genetic structure, I analysed mitochondrial DNA genes from limpet species of the Cellana genus. Phylogenetic analyses of the ribosomal 12S and 16S DNA genes showed that C. ornata may approximate the founding lineage to New Zealand, but these genes were unable to resolve between contrasting biogeographic hypotheses about the origin of Cellana in New Zealand. Intraspecific analyses of the mitochondrial cytochrome b gene from populations throughout the biogeographic range of Cellana ornata, C. radians and C. flava showed concordant genetic discontinuity at Cook Strait. Further analyses suggest that allopatric fragmentation and restricted gene flow have caused significant genetic differentiation between populations of the North and South Island. Demographic expansion was also identified for C. radians. The influence of contemporary nearshore currents and sea surface temperature was assessed using the mitochondrial cytochrome b gene for C. radians and C. ornata. Low levels of genetic differentiation between populations corresponding to 'current-zones' suggests that contemporary oceanic processes may be contributing to the genetic pattern observed for these species. However, the shallow divergence between haplotypes and populations restricted thorough investigation of contemporary gene flow. Genealogical concordance across co-distributed marine taxa of New Zealand also lends support to the historic association of genetic and species discontinuities with recent geological changes, such as sea level fluctuations.