Browsing by Subject "Systematics"
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- ItemOpen AccessExamining patterns of coexistence in the Cape genus Tetraria (Cyperaceae) from a phylogenetic perspective : tracing the history of community assembly processes(2004) Slingsby, Jasper; Verboom, George AnthonyThe coexistence of species is fundamentally important in maintaining high species diversity in a defined area, and is partly responsible for the remarkable diversity of the Cape Floristic Region. The ecological attributes that determine the community assembly processes of competitive interactions and ecological sorting are subject to phylogenetic constraint and niche conservatism, suggesting that patterns of coexistence should be phylogenetically structured. This study compares patterns of coexistence against phylogenetic and ecological divergence in the genus Tetraria (Cyperaceae), and related sedges in the tribe Schoeneae, at different spatial and phylogenetic scales in multiple communities across the Cape Fynbos Biome. The investigation is based on coexistence data inferred from plot data from 13 phytosociological studies, ecological distances based on plant functional traits, and phylogenetic distances based on a molecular phylogeny of the species in question. Species coexisting in plots are significantly less related than expected on the basis of chance, and plots of phylogenetic distance against coexistence show triangular relationships, implying coexistence between closely related species is restricted, but that coexistence levels between more distantly related species may vary greatly. Quantification of these triangular relationships was problematic due to the small sample sizes and the low power of the nonparametric tests used. The pattern is more pronounced when a closely related subset of the species was used in a separate analysis, suggesting that phylogenetic scale is important. Coexisting species are significantly more closely related at the study than at the plot scale, implying relaxation of the effects of competitive interactions at coarser spatial scales. Significant positive correlation between ecological and phylogenetic divergence implies that phylogenetic constraint and niche conservatism has a strong effect on the ecological attributes of the study species. These results provide support for the hypothesis that the patterns of coexistence among species' in the genus Tetraria, and related sedges in the tribe Schoeneae, are influenced by phylogenetic constraint and niche conservatism on ecological attributes.
- ItemOpen AccessIntraspecific variation and ecology of a highly restricted paleoendemic (Witsenia maura) in the south-western Cape(2003) Gwynne-Evans, David; Hedderson, Terry AWitsenia is a monospecific genus of the putatively basal group, the woody Iridaceae. This upright iris has extremely long black and yellow flowers ( see fig. 1) that are thought to have been pollinated by an extinct Sunbird. The role of the unusual black floral colouration is investigated as this colour is seldom associated with bird pollination. This plant typically exists in discreet and restricted populations in wet habitats in the South Western Cape (South Africa). The restricted nature of the plant is peculiar as it occurs in either low or high altitudes, yet appears to be extremely sensitive to altitude. Popular belief suggests that Witsenia maura occurs in the Peninsula only, and results from this study show the Peninsula population to be genetically separate from other populations, reflecting a long term separation. Samples from nine populations are sequenced to investigate haplotypic variation within the species, and dispersal of ancestral populations. This thesis investigates the current knowledge of Witsenia, its ecology, history and distribution. An examination of flowers under UV light reveals the first evidence of UV nectar guides in an ornithophilous flower. Conservation issues are also addressed, and it is established that although small and apparently shrinking due to global warming, populations are nonetheless viable if managed properly. A molecular study of the species and examinination of its variation revealed exceptional haplotype diversity. This diversity can best be explained by swamps acting as refugia during interglacial periods.
- ItemOpen AccessPhylogeographic structure in the CFR genus Pauridia revealed by inter-simple sequence repeat amplification(2005) Burman, Marc; Hedderson, Terry AThe Cape Floristic Region, South Africa, has high numbers of rare and endemic plants. Many, including Pauridia Harv., are geophytes in the Hypoxidaceae. The two species of Pauridia differ in morphology and range, with P. minuta occupying a wide range across lowland CFR and P. longituba being restricted to granite outcrops on the West coast. Genetic structure correlated to geography has been described for the haploid chloroplast genome. Here the diploid nuclear genome is investigated using inter-simple sequence repeat amplification. Eleven populations were sampled from DNA collected for a previous study. Analysis of molecular variance was done. Ordination based on similarity and covariance was done to detect structure. Most of the variance was found to be within populations (65.54%) and between populations within groups (35.69%). Some variance (10.10%) was found between P. minuta geographic groups. Principal Component Analysis revealed a little structure, grouping some similar haplotypes together. Cluster analysis placed P. longituba within P. minuta, reflecting the haplotypic structure. Differences in structure revealed between the chloroplast and nuclear genome may be explained by differences in gene flow resulting from the different modes of inheritance - chloroplast via seed and nuclear via pollen and seed. Further analysis of genetic distance correlations between the chloroplast and nuclear data would provide a useful quantitative measure of difference in structure.
- ItemOpen AccessQuestioning the Cunonia in C. capensis(1995) Kruger, Lynette; Linder, H PeterAll members of Cunonia, excluding C. capensis, occur on the island of New Caledonia. Dickison has repeatedly noted (1973, 1975, 1980, and 1984,) that evolutionary patterns may have led to incorrect systematic conclusions among many cunoniaceous genera, which are likely to generate incorrect systematic conclusions. For this reason, a study into the morphological characters defining C. capensis was undertaken. Although the possibility that the disjunct biogeographical pattern of C. capensis might be explained on the basis of taxonomic error was appealing, it was not conclusively supported from this investigation. Instead it was found that of the six characters supposed to distinguish Cunonia from Weinmannia, three agreed with the present position of C. capensis with Cunonia, whilst the other three placed C. capensis with Weinmannia. This study also served to highlight the need for further investigation and identification of characters which separate Cunonia and Weinmannia at the species level.