OpenUCT :: Browsing by Subject "Systematics and Biodiversity Sciences"

Browsing by Subject "Systematics and Biodiversity Sciences"

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Open Access
Aloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change?
(2004) Duncan, John A; Hoffmann, Timm
Aloe pillansii populations in the biodiversity hotspot of the Succulent Karoo in Southern Africa are thought to be under threat of extinction. This study investigated the population at the type locality; Cornell's Kop in the Richtersveld, South Africa. It has been suggested that theft, animal damage and more recently climate change have caused a decline in the population by over 50% in the last decade, however very little is known about this rare species. Repeat photography and surveys were used to analyse life history patterns and dynamics of the population and thus establish what the potential threats to this keystone species actually are. Repeat photography indicates that there have been high rates of adult mortality over the last fifty years (1.8% of the population dies annually), which results in an average predicted lifespan of 39 years for the remaining adult population on Cornell's Kop. However, a recent survey reported that over 40% of the population recorded were seedlings, which weren't found in a 1995 survey, which is indicative of a recent recruitment pulse on Cornell's Kop and that conditions on the hill are still habitable for A. pillansii. Growth analyses suggest that A. pillansii has an average annual growth rate of 20 mm.yr⁻¹, which in tum means that 8 m individuals may be up to 453 years old. This long-lived strategy would require A. pillansii to only recruit infrequently, during periods of high rainfall, in order to sustain a viable population, which is consistent with findings on other large desert succulents. Seedling ages were estimated from their heights and it was found that 50% of the seedlings appear to have germinated five to ten years ago; this is consistent with rainfall records from the area which indicate that rainfall was consistently above the annual average for this same period. The findings indicate that although the adult A. pillansii population is declining, the presence of 30 seedlings suggest that the population is entering a recruitment phase after just coming out of a lengthy senescent phase. Although A. pillansii 's extensive lifespan makes it a potentially useful indicator species of climate change, the evidence presented in this study does not suggest that climate change has affected the dynamics of this population.
Open Access
An alternative hypothesis for explaining anomalies in the fine scale distribution patterns of Colophospermum mopane : Are shrub and tree forms genetically distinct ?
(2004) Hempson, Gareth; Verboom, George Anthony; February, Edmund C
Abiotic and top down control hypotheses do not adequately explain the fine scale distribution patterns of shrub and tree Colophospermum mopane (Caesalpinioideae). Genetic distinctiveness between growth forms is investigated as an alternative hypothesis. Tree and shrub C. mopane from the riparian and inland savanna zones were sampled at four sites in the northern Kruger National Park. Molecular DNA sequences were obtained for four plastid and one nuclear region, and the inter simple sequence repeat (ISSR) technique used to fingerprint individuals. Very low levels of sequence divergence were observed. The ISSR technique revealed no genetic structure between plants when grouped by growth form or by habitat in an analysis of molecular variance (AMOV A). Soil profile and xylem pressure potential data also did not explain the distribution of growth forms. A principle component analysis and a discriminant analysis of five leaf and branching characters identified a significant difference in the shape of shrub and tree C. mopane leaves. It is concluded that the C. mopane growth forms are not genetically distinct and that their fine scale distributions may be due to top down controls such as large mammals and fire.
Open Access
Bryophyte diversity patterns in a fragmented landscape : a case study of South African West Coast renosterveld
(2006) Rugengamanzi, Nkubana Felecian; Hedderson, Terry A
This study examines the effects of fragmentation on bryophyte diversity in renosterveld vegetation of South Africa's west coast. The main objectives of this study are to; Document bryophyte species assemblages in remnant fragments of renosterveld vegetation, investigate the effect of fragment size, isolation and heterogeneity on bryophyte diversity patterns in renosterveld, determine the extent to which fragments are nested and evaluate the extent to which existing conservation measures are appropriate for the long-term survival of the bryophyte flora in this vegetation type. Seventy-two bryophyte species were recorded from 23 fragments ranging from 0.1 to 102 hectares.
Open Access
Do Savanna acacias nodulate as seedlings?
(2006) Szoke, Tim
Open Access
The effects of leaf harvesting on the morphology, reproduction and sap production of the Cape Aloe (Aloe Ferox)
(2004) Greengrass, Catherine; Chadwick, Peter J; Hoffmann, Timm
Harvesting of Aloeferox was estimated (in 1996) to bring in an annual income ofR4 million per year to rural communities alone - a vital source of income for full-time tappers who rely solely on Aloe ferox as their only form of financial survival. They are joined on occasion by casual-tappers who rely on tapping to supplement their incomes in times of hardship (Newton and Vaughan 1996). Landowner's also benefit by allowing harvesting on their land in exchange for a percentage of the harvest (Newton and Vaughan 1996). Trade in bitters sap or gel far outweighs that of other plant parts so care is taken by harvesters to keep the plants alive for future tapping. Leaves from only the lower third of the leaf rosette ( 10 - 15 leaves) are harvested, and 2 - 4 cm at the base of the leaves are left to prevent damage to vascular tissues (Newton and Vaughan 1996, Mac Farlane 2004). Populations are only harvested every 18 - 36 months allowing plants to recover from the loss of leaf material. Plants suffering from insect-infestation or disease are not harvested to avoid weakening the plant further and possibly causing death (Newton and Vaughan 1996). Effort is also made by landowners to relocate plants growing in areas they plan to transform and to monitor harvesting activities on their properties (Newton and Vaughan 1996). The vested interest in keeping the plants alive has inadvertently assured the preservation of populations at past harvesting levels although no formal conservation or resource management policy presently exists for A. ferox (Newton and Vaughan 1996). Effects of harvesting, which are not limited to the direct effect of leaf removal on the plant but include indirect effects - such as reduced reproductive output, reduced sap production and even trampling of recruits - have nonetheless raised concern for the long-term survival of populations (Newton and Vaughan 1996). This study addressed some of the indirect effects of harvesting on Aloe ferox on both population and individual plants levels. On the population level plant density, mortality, susceptibility to disease and sizeclass structure was compared between unharvested and harvested populations. On the individual plant level vegetative traits, flower production and sap production were compared between unharvested and harvested plants. One of few other studies on ecology of A. ferox by Hoffman (1988) assessed some of these characteristics for a population in Port Elizabeth, South Africa.
Open Access
Fire regime and tree/shrub/grass balance at Pretoriuskop in the Kruger National Park: Evidence from ground photographs
(2003) Ntsohi, Refiloe
Open Access
Friend or foe? : the invasive potential and aquacultural application of the sporophytic Falkenbergia stage of Asparagopsis armata in South Africa
(2004) Duncan, John A; Bolton, John J; Anderson, Robert J
The presence of the sporophytic 'Falkenbergia rufolanosa' phase of the invasive algal species Asparagopsis armata was first recorded in South Africa 57 years ago. The introduction of this highly invasive alga, of Australian/New Zealand origins, to Europe in the 1920's has since led to a number of recorded invasions by the gametophytic Asparagopsis phase in both the Mediterranean and Atlantic oceans. Recently however, a number of commercial uses for both phases of A. armata have been identified, which have given rise to industrial interest in the species as a candidate for commercial cultivation. Previous studies on European strains of F. rufolanosa and A. armata have identified a number of life history traits, which not only increase A. armata 's invasive ability, but also make it a useful species for commercial tank cultivation. However, different strains are known to have different environmental parameters which regulate their survival, growth and reproduction capabilities. This study investigated the growth of the South African strain of F. rufolanosa in culture, in response to different environmental variables, as well as the conditions necessary for tetrasporogenesis to occur, in order to assess its potential impacts, both as an invasive threat and as a species for commercial cultivation in South Africa.
Open Access
Further studies with Melianthus L. : a molecular phylogeny, evolutionary patterns of diversification in the genus and pollinator syndromes
(2003) Henning, Jack; Verboom, George Anthony; Hedderson, Terry A
A phylogeny was produced for the eight taxa comprising the largely South African genus Melianthus L. based on two plastid markers (trnL-F and psbA-trnH) and one nuclear marker (ITS). Topological comparisons with a tree based on an existing morphological data set revealed significant incongruence leading to a loss of resolution upon combination. Ultimately, the combined three-gene data tree was selected as the strongest phylogenetic estimate for Melianthus based on its better resolution and greater support levels. This tree confirms the monophyly of Melianthus with M. major being resolved as sister to the remainder of the genus. Within the remaining clade, M. villosus is resolved sister to a clade comprising two morphologically distinct subclades, one of these being noted for a western distribution (comprising M. elongatus and the M. pectinatus complex), the other being centred farther east (comprising M. cocomosus and the M dregeanus complex). A molecular clock analysis was employed to date the emergence of specific taxa and clades, while ancestral range and habitat reconstructions were performed to determine historical conditions under which these groups and their morphological novelties arose. A scenario depicting the evolution and diversification of Melianthus is developed against a backdrop of the paleo-history of southern Africa. The genus appears to have originated in the eastern part of South Africa during a mild, mesic Oligocene with subsequent westward expansion into drier habitats of Miocene and Pliocene origins. Observations of bird visitors to a range of Melianthus species indicate that the genus employs a generalist pollination syndrome, thus refuting suggestions of a co-exclusive relationship with sunbirds (Nectariniidae). Nevertheless, the genus is undeniably ornithophilous. Nectar studies reveal interspecific variation in both the volume and concentration of nectar produced as well as in nectar colourition.
Open Access
Genetic introgression and female mate choice within the Calendulauda albescens/C. barlowi hybrid zone
(2004) Oatley, Graeme; Crowe, Timothy M
The hybrid zone between Calendulauda albescens and C. barlowi, located near the Orange River, contains a wide range of phenotypically intermediate individuals. This study examines the mitochondrial DNA of some of these individuals to determine if possible introgression is occuring from C. albescens to C. barlowi. Mitochondrial DNA from 13 lark individuals found in the C. albescens/C. barlowi hybrid zone was analysed. A 358 base pair cytochrome-b sequence was obtained. The neighbour-joining phylogenetic tree obtained revealed two distinct clades, a C. albescens and C. barlowi clade. The C. barlowi clade was supported with a bootstrap value of 100. The C. albescens clade contained individuals of intermediate morphology, as represented by their hybrid index scores, indicating that intermediates between the two species contain the mitochondrial DNA of only one species, C. albescens. These results point at introgression from C. albescens to C. barlowi, with female C. albescens choosing to mate with male C. barlowi.
Open Access
A hierarchical phytosociology of the Greater Zandvlei area
(2006) Szöke, Tim; Hoffmann, Timm
The Zandvlei Nature Reserve is to be expanded to form the Greater Zandvlei Estuary Nature Reserve and will encorporate a much greater area (250 more hectares). The Greater Zandvlei area was classified by means of Zurich Montpellier (Braun Blanquet) procedures. 60 relevés were used to create a hierarchical phytosociology using TWINSPAN and DCA-ordination analyses. 3 major community types were identified, which were then subdivided to reveal 6 community types important to future management: Moist Grassland/Wetland Disturbed Parkland, Dune Asteraceous Fynbos, Thicket/Shrub Mosaic, Rhus-Euclea Dune Thicket and Homogenous Patches. CCA-ordination indicates that the abiotic soil factors sampled (texture composition, pH, carbon content and visible disturbance) explain very little of the variation between the communities (r²=0.002). This phytosociology is provided as a tool for future research in the area, and it is hoped to assist in future management decisions regarding the newly founded GZENR.
Open Access
Immunogold labelling of TIP proteins in the resurrection plant Craterostigma plantagineum
(2000) Maguire, Victoria
Open Access
Long-term salinity trends in Zandvlei estuary and implications for dominant macroalgae
(2003) Muhl, Sara; Bolton, John J; Hoffmann, Timm
Zandvlei is a system that has been highly modified by the urban environment of Cape Town. Salinity is a major driver determining the physical environment of estuaries. The macroalgal community of estuaries forms an important part of the ecology of these systems as primary producers. The salinity of this environment is an important parameter determining the composition, abundance and diversity of these communities. Patterns of salinity fluctuations in the long term (1978-2003) and annually are described in order to establish how communities may vary. Zandvlei is in a Mediterranean climate and salinity was found to vary seasonally and monthly with fluctuations in rainfall. Historical records of macroalgae identified in the estuary were summarized and no record of the Polysiphonia sp., now dominant in the estuary, was found. Dominant macroalgae in the estuary were identified and grown under a range of salinities (0, 1, 5, 10, 20, 29 ppt). Dominant macroalgae included Cladophora sp., Polysiphonia sp. and Enteromorpha prolifera. None of these algae survived at O ppt. In 1 ppt E. prolifera survived but growth was retarded, Polysiphonia sp. survived but did not grow and Cladophora sp. grew successfully at this salinity. All three species have different optimum ranges for growth with E. prolifera preferring higher salinities, Cladophora sp. grew similarly across the range from 1 to 29 ppt and Polysiphonia sp. grew most rapidly at 5 ppt. Depending on the salinity range in the estuary different macroalgae will be dominant. This makes the macroalgae community quite resilient to fluctuating salinities. There should therefore always be estuarine macroalgae present in the estuary provided salinity does not drop below 1 ppt for an extended period. If salinities did drop below 1 ppt there could be an increase in freshwater algae.
Open Access
Molecular and morphological phylogenetic analyses of Euphorbia L. (Euphorbiaceae) with an emphasis on Southern African representatives
(2003) Mapaya, Ruvimbo Jessy; Hedderson, Terry A; Bruyns, Peter V
The genus Euphorbia is morphologically diverse and nearly cosmopolitan. Both succulent and non-succulent species are found within the genus. Succulent species are found in most arid and semi-arid areas of the world, but show their greatest concentration and diversity of form in Southern Africa especially the Cape Floristic Region. The monophyly and phylogenetic relationships of the genus Euphorbia were investigated based on morphology and on sequences of the nuclear ribosomal internal transcribed spacer (ITS) and chloroplast psbA-trnH intergenic spacer. Fifty-one species of Euphorbia and four outgroups from Monadenium and Ciutia were sampled. Matrices were analysed using parsimony and maximum likelihood methods. Separate analyses of data partitions resulted in largely non-conflicting topologies; therefore the data sets were combined. The results showed that the genus Euphorbia is paraphyletic and four monophyletic groups with a number of putative synapomorphies defining each clade were strongly supported in most analyses. The Cape succulents fall into two well-supported clades. The results thus provided evidence for Cape radiations. Most analyses indicated that one of the Cape groups is sister to a group consisting of species mostly from Southern Africa (excludingthe Cape Region). Increased taxon sampling is however needed to clarify relationships within the monophyletic groups. Morphological characters recovered broad groups within Euphorbia. Due to inadequate sampling in some sections, modifications in the present classification of Euphorbia are not suggested. The total evidence tree was used to explore morphological character evolution through character state optimisations. The presence of root tubers was homoplasious and this character state is hypothesized to have arisen at least five times under current sampling. Cylindrical stems, conspicuous leaves and absence of leaf spines were some of the pleisiomorphic states observed in some sampled members of the genus Euphorbia. Although the results obtained in the CUlTent study are preliminary, they have created further challenges for future studies of phylogenetic relationships and morphological character evolution in the genus Euphorbia.
Open Access
Molecular phylogeny of Tribolium (Danthonioideae: Poaceae) and its taxonomic implications
(2003) Ntsohi, Refiloe; Verboom, George Anthony
Molecular sequence data from two noncoding regions of DNA (ITS AND TRNL-F) were used to produce a phylogeny for the genus Tribolium and its African and Australasian allies. Topological comparisons of the combined molecular data with the appended existing morphological tree were made. A significant incongruence was revealed. Molecular data indicate that Tribolium is paraphyletic. The formally defined sections: Uniolae, Acutiflorae and Tribolium have been retrieved by the molecular data. The analysis retrieved Karroochloa as polyphyletic. Monophyly of Schismus is strongly supported. The Australasian species form a monophyletic clade. Data support early divergence of the Merxmuellera species and Pseudopentameris macrantha.
Open Access
The molecular systematics of Ulva Linnaeus and Enteromorpha Link (Ulvales, Chlorophyta) from the South Western Cape, South Africa
(2002) Kandjengo, Lineekela; Bolton, John J; Hedderson, Terry A
Both Ulva and Enteromorpha are very common, ubiquitous, and environmentally important genera of green seaweeds. The evolutionary history of Ulva species is poorly understood, stemming from a lack of diagnostic, non-molecular systematic characters. This study addresses the following questions: i) Do the two genera represent distinct entitiesj ii) What are the relationships among local putative species; iii) Do the recognized species represent monophyletic lineages; iv) How closely are local species related to those from elsewhere? These questions are addressed using nuclear ribosomal DNA ITS sequences from 48 local samples plus data on 16 samples from GenBank.
Open Access
Phylogenetic relationships of the African species of the genus Merxmuellera Conert (Poaceae: Danthonioideae)
(2001) Mafa, Paseka; Linder, Peter; Barker, N P
This study expands on existing molecular (rpoC2 and ITS) and morphological data sets to further test the hypothesis of non-monophyly of Merxmuellera sensu lato. The results reveal that despite high levels of resolution, the morphological data yield poorly supported phylogenies due to high levels of homoplasy in the dataset.
Open Access
Phylogenetic studies in the genus Jamesbrittenia tribe Manuleae, family Scrophulariaceae
(2006) Herron, Margaret; Verboom, Tony
Jamesbrittenia is a genus of 84 largely perennial sub-shrubs and herbs with a wide distribution in southern Africa (except J. dissecta in Sudan, Egypt and India). Plastid (rps16 and psbA-trnH) and nuclear (GScp) sequences were obtained for 42 species, mostly from the arid winter-rainfall west and southern regions of southern Africa. Applying both parsimony and Bayesian inference to combined molecular and morphological data sets, a phylogenetic hypothesis which is robust at the deeper nodes, was produced. This supports the monophyly of Jamesbrittenia, and also indicates the early divergence of J. ramosissima and three major clades.
Open Access
Phylogeographic patterns in three South African forest mosses
(2003) Mwafongo, Elizabeth; Hedderson, Terry A
Lepfodon smithii (Leptodontaceae) and Pterogonium gracile (Leucodontaceae) are widespread and disjunctly distributed moss species, that in South Africa are confined to forest patches believed to be relics of vast forests that existed before the Pleistocene glaciation period. These two species exhibit similar distribution and ecologies and frequently co-occur. Wardia hygrometrica is a southwestern Cape endemic that is restricted to streams within the kloofs that the forests generally occupy. In an attempt to trace the species histories and their subsequent colonization of forest patches, two molecular markers, internal transcribed spacer (ITS) nuclear rDNA and trnL-F cpDNA were employed.
Open Access
The potential for Gracilaria polyculture at Jacobs Bay Sea Products Pty
(2000) Morgan, Derek; Anderson, Robert J; Bolton, John J
This report investigates the potential for the culture of G. gracilis, an indigenous red alga, into the west coast mariculture farm Jacobs Bay Sea Products Pty. Various methods for cultivating Gracilaria as well as environmental parameters, which influence growth of Gracilaria, are disltussed below. From these optimal conditions for the polycultivation of G. gracilis are determined. Cultivation can take place either, in open waters, or on land. Open water systems are generally less intensive than land based operations. Open water systems can be either bottom planted or suspended. Suspended cultivation has the advantage of maintaining the plant thalli in optimal light intensities. Land based systems can make use of ponds, raceways or tanks. Tanks and raceways are more productive than ponds, but require higher ﬂow rates and regulated nutrient regimes.
Open Access
Quantifying Acacia defences : understanding the role of hooks, spines and architecture
(2004) Hempson, Gareth; Kruger, Laurence; Bond, William J; Midgley, Jeremy J
The effectiveness of the structural defences of Acacias vary within and between species as a result of differences in thorn type (hooks versus spines) and branching architecture. This study aims to develop methods for quantifying the effectiveness of defences, thereby allowing for comparisons between individuals and localities. Measurements of a range of thorn and branching parameters of eight Acacia species were used to calculate three indices (stripping, biting and branching) describing different components of Acacia structural defences. These were combined to form an overall defence index that was tested against the results of three feeding simulation tests as well as actual animal feeding rates obtained from trials using nyala held in bomas. The stripping, biting and branching indices were shown to provide a good measure of the different components of a structural defence, although the scaling of their contribution to an overall defence index is complicated by variation in the suite of browsers and the resources available at a locality. The indices developed in this study provide a useful tool for assessing the role of large mammal herbivory in different environments when attempting to understand variation in the life history strategies of Acacias.