3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Towards an understanding of plant rarity in Kwazulu-Natal, South Africa(2014-07-31) Church, BrigitteThe persistence of rare plants is an important dimension in the conservation of biodiversity. Consequently an improved understanding of the nature and determinants of plant rarity and its relation with vulnerability to extinction could provide a basis for “proactive conservation” instead of the present day tendency for conservation actions to be “reactive”. In this dissertation I explore the relation between plant rarity and anthropogenic pressures (land transformation and use), biophysical factors, and plant traits in KwaZulu-Natal Province. Rarity was defined as the product of plant species abundance (population size) and its distribution (extent of occurrence). A number of a priori hypotheses regarding plant rarity were developed from the literature and these were then tested on a sample of plant species from KwaZulu-Natal. Species were selected in a stratified random manner to include species from different levels of threat and rarity or commonness. As the interest of this study was KwaZulu-Natal, only KwaZulu-Natal records were used for the analysis. Although the study suffered from a paucity of data particularly on the biological traits and behaviour of each species I was able to explore rarity in terms of seed dispersal distance, stress tolerance, habitat specificity and ecological niche width. I also explored potential island effects based on a species affinity to isolated erosional land surfaces and the anthropogenic effects of utilization and land transformation. To get an initial insight into relations, rarity was compared with each explanatory variable independently prior to using a multiple regression analysis approach aimed at understanding the potential interactive effects of suitable variables on rarity. Three different analytical techniques were used to provide a more robust understanding of the variable associations. These included Regression tree analysis (CART Salford Systems Inc., USA) and two generalized linear regression approaches; Generalized Linear Modelling (GLM) and Generalized Additive Modelling (GAM). All three multiple regression methods indicated that niche width had the strongest influence on rarity. Although Land Surface was shown to be the second strongest variable this, according to the GLM and GAM analyses, was due to a positive correlation between species with no affinity to land surface and species commonness. Visual representation of the regression tree analysis showed inconsistent partitioning of this variable throughout the tree indicating that land surfaces are not good predictors of rarity. Although the relation between Rarity Index and Habitat Transformation is not linear it was shown to be significant (p <0.1(p=0.0549)) after “smoothing” in GAM analysis. A smoothing curve on the bivariate analysis and the regression tree analysis indicated that species start to become rare after approximately 36% of their habitat is transformed. While GLM and GAM showed little or no relation between life history, dispersal distance, habitat specificity and rarity, the regression tree selected habitat specificity as the third most important splitter in the tree and dispersal distance was selected as a primary splitter for species with a niche width of greater than four. These differences observed in the three multiple regression analyses highlight the value of using more than one method to explore relations in ecological data. Considering all three analyses Niche Width is the strongest determinant of Rarity in KwaZulu-Natal, followed by Habitat Transformation and then Habitat Specificity. This improved understanding of the determinants of rarity will enhance our ability to prioritise plant species for conservation action. Key Words: ecological niche width, habitat specificity, habitat transformation, rarity, seed dispersal distance, stress tolerance, human use.Item Middle Permian continental biodiversity changes as reflected in the Beaufort Group of South Africa: a bio-and lithostratigraphic review of the Eodicynodon, Tapinocephalus and Pristerognathus assemblage zones(2014-03-04) Day, Michael OliverThe fluvio-lacustrine rocks of the Beaufort Group, South Africa have long been known for their tetrapod fossil record, which is the richest and most complete Middle Permian to Middle Triassic record for any terrestrial sequence in the world. The abundance of fossil material has enabled the Beaufort Group to be biostratigraphically subdivided into between 8 and 10 tetrapod assemblage zones, of which the lowest three (Eodicynodon, Tapinocephalus and Pristerognathus) are attributed to the Middle Permian. These lower assemblage zones record the earliest therapsiddominated faunas and, because they were recorded during a largely uninterrupted period of deposition, make the Beaufort Group the only place in the world where biodiversity change through the terrestrial Middle Permian can be effectively studied. In the last two decades, much interest has focused on an extinction of marine invertebrates at or close to the end of the Middle Permian (Guadalupian epoch), but the existence of a concurrent extinction in the terrestrial realm is contentious. The Beaufort Group is already well known to record the Permo-Triassic Mass Extinction but it also records an earlier extinction at the top of the Tapinocephalus Assemblage Zone (AZ). This extinction is very poorly understood but recent radiometric dates for many Permian assemblage zones of the Beaufort Group have confirmed a Middle Permian age for Eodicynodon, Tapinocephalus and Pristerognathus assemblage zones and suggest that the end-Tapinocephalus AZ extinction may coincide with the marine extinctions. A recently produced GIS database that accommodates all Beaufort Group fossil material curated in South Africa formed the basis on which the stratigraphic range of individual specimens was calculated. To put the fossil localities in a stratigraphic context, lithostratigraphic information was retrieved from the literature and extensive fieldwork was conducted, which measured stratigraphic sections in key areas and traced the surface outcrop of lithostratigraphic units. In order to compensate for lateral variations in lithostratigraphy, the basin was split into sectors, each represented by a stratigraphic section. The stratigraphic ranges of fossil specimens and, subsequently, of genera and families could then be calculated and a workable biostratigraphic subdivision of the Middle Permian Beaufort Group proposed. The Abrahamskraal Formation, which forms the majority of the Middle Permian Beaufort sequence, can be divided into six lithostratigraphic members based on the occurrence of sandstone ‘packages’. These members were traced laterally across the Basin and their correspondence with fining-upwards cycles was refined and correlated with the newly defined biostratigraphic units. This refined two-pronged stratigraphic subdivision allowed the recognition of a waning period of subsidence in the proximal sector of the Karoo Basin during the Middle Permian. Stratigraphic ranges of individual genera were found to be far more heterogeneous than previously recognised. Dicynodont genera are useful biostratigraphic indicators due to their relative abundance and well-defined stratigraphic ranges, while dinocephalians and pareiasaurs are clustered in the upper part of the Abrahamskraal Formation. The stratigraphic range of Eodicynodon extends further up in the Abrahamskraal Formation than was previously recognised. The Tapinocephalus AZ is restricted to approximately the upper fifth of the Abrahamskraal Formation and is characterised by advanced tapinocephalid dinocephalians and the pareiasaur Bradysaurus. Between these two biozones is a stratigraphic interval dubbed the mid- Abrahamskraal Formation Transition Zone, where both Eodicynodon and advanced tapinocephalids coexisted. A 75 % loss of generic diversity occurred between the upper Tapinocephalus AZ and the base of the Pristerognathus AZ, which corresponds to a stratigraphic interval between the mid-Karelskraal Member of the Abrahamskraal Formation and the mid- Poortjie Member of the Teekloof Formation. Several taxa that survive the end- Tapinocephalus AZ extinction, and are relatively common in the overlying Pristerognathus AZ (scylacosaurid therocephalians, the dicynodont genus Eosimops and the parareptile Eunotosaurus), all became extinct in the upper Poortjie Member at a time when generic originations are increasing. This suggests a second wave of extinctions in a similar fashion to that recorded at the Permo-Triassic boundary.