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- ItemThe ability of terrestrial Oligochaeta to survive in ultramafic soils and the assessment of toxicity at different levels of organisation(Stellenbosch : University of Stellenbosch, 2006-12) Maleri, Rudolf A.; Reinecke, A. J.; Reinecke, S. A.; Mesjasz-Przybylowicz, J.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.Metals are natural elements of the earth crust usually present at low concentrations in all soils. Although many metals such as cobalt, copper, iron and zinc are essential to living organisms, at elevated concentrations most metals are toxic to organisms living in and on soils. Elevated concentrations of metals are caused either by anthropogenic deposition following remobilisation from the earth crust or are of natural origin. Ultramafic soils do not only pose unfavourable living conditions such as drought and poor organic content, these soils are also characterized by extremely high concentrations of a range of metals known to be toxic under normal circumstances. Ultramafic soils are of high ecological importance as a high proportion of endemic organisms, especially plants, live on these soils. As it is known that earthworms do occur in ultramafic soils, the aims of the present study were to investigate the abilities of earthworms to survive in these soils and the influences of elevated chromium, cobalt, copper, manganese and nickel levels. For the evaluation of the metal background conditions, soils originating from ultramafic rocks of the Barberton Greenstone Belt, Mpumalanga, South Africa were collected and different fractions representing different levels of bioavailability were analyzed for arsenic, chromium, cobalt, copper, manganese and nickel. To assess the mobile, readily available metal fraction, i.e. Ca2+- exchangeable metal cations, a 0.01 mol/L CaCl2 extraction was performed. To investigate the mobilisable metal fraction, representing the amount of easily remobilisable complexed and carbonated metal ions, a DTPA (di-ethylene-triamine-pentaacetic acid) extraction was conducted. In relation to non-ultramafic or anthropogenic contaminated soils, a far lower proportion of metals were extractable by the above mentioned extraction methods. To investigate the availability and effects of these metals on earthworms, two ecophysiologically different species were employed. Aporrectodea caliginosa and Eisenia fetida were long-term exposed to the ultramafic soils collected at the Barberton region and a control soil from a location at Stellenbosch with a known history of no anthropogenic metal contamination. The responses to the ecological stress originating in the ultramafic soils were measured on different levels of earthworm organisation. As endpoints affecting population development, cocoon production, fecundity and viability were evaluated. On individual level, growth, metal body burden and tissue distribution were investigated. As endpoints on subcellular level, the membrane integrity was assessed by the neutral red retention assay, the mitochondrial activity was measured by the MTT colorimetric assay and as a biomarker for the DNA integrity, the comet assay was performed. Focussing on manganese and nickel, the uptake by E. fetida of these metals was investigated with the exclusion of soil related properties using an artificial aqueous medium to draw comparisons to the uptake of these metals in natural soils. The possible development of resistance towards nickel was tested by exposing pre-exposed (for more than 10 generations) E. fetida specimens to ultramafic soils with concentrations of more than 4000 mg/kg nickel. The results showed that, except on the endpoint survival, which was less sensitive than all other bioassays, significant responses to the ultramafic challenge were observed in all earthworm bioassays and on all levels of organisation. The sensitivity of the responses of the earthworms towards the ultramafic conditions was not predictable by the level of organisation. The two species showed different strategies of metal elimination. In A. caliginosa, metals such as nickel, manganese and chromium were transported to the posterior section and the posterior section was subsequently pushed off by autotomization. In E. fetida, metals such as chromium and nickel were sequestered in storage compartments in the coelomic cells or fluid. Other metals, such as cobalt, were not taken up at elevated concentrations. Although an increased accumulation of nickel was observed in E. fetida specimens pre-exposed to nickel, development of resistance or cross resistance was not observed in this species. In contrast, pre-exposed specimen exposed to elevated concentrations of nickel showed a higher sensitivity in terms of survival, indicating the absence of acclimatisation or even genetic adaptation. A comparison of the two species employed indicated that A. caliginosa was less suited for the assessment of the ultramafic soils due to the high individual variation in metal body burden, the mass loss observed and the slow reproduction rate even in the control soils. This happened despite the fact that A. caliginosa was a soil dwelling species supposed to be better adapted to the soil substrate than the litter dwelling E. fetida. The toxicity of the ultramafic soils was not necessarily related to total or environmentally available amounts of the selected metals. Thus, it can be speculated that either these soils contained unidentified toxicants with resulting interactions between toxicants playing an important role or earthworms were able to remobilize metals occurring in these soils. As the singular application of an ecotoxicological endpoint did not give reliable results, especially seen over the duration of the exposures, it can be concluded that, when studying soils with such a complex composition, the utilisation of endpoints addressing different levels of organisation is necessary for the assessment of toxic stress emerging from these ultramafic soils.
- ItemThe abundance and diversity of meso- and macrofauna in vineyard soils under different management practices(Stellenbosch : Stellenbosch University, 2005-03) Nel, Werner; Reinecke, A. J.; Reinecke, S. A.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: The agricultural sector in South Africa relies heavily on the use of pesticides to protect crops against pest organisms. Pesticides can affect non-target organisms such as the meso- and macrofauna in the soil detrimentally. Since these organisms play an important role in the processes of mineralization and decomposition in the soil and contribute to soil fertility, it is important that they are protected. A large amount of published literature exists on the biological importance of soil meso- and macrofauna and the effects that various agricultural practices have on them. The main aim of this study was to investigate the influence of agricultural practices on the abundance and diversity of meso- and macrofauna in different vineyard soils. A comparative study was conducted of an organically managed, conventionally managed and an uncultivated control soil. A secondary aim was to determine the effect of these agricultural management practices on the biological activity of these animals. Soil samples were taken, from which mesofauna (Collembola and Acari) were extracted with a modified Tullgren extractor, identified and counted. Earthworms were extracted from the soil using hand sorting methods. Soil parameters such as pH, water holding capacity, organic matter content, soil texture and soil respiration were determined. Bait lamina and litter-bags were also used to help determine the biological activity within the soil. The mesofauna diversity was quantified using the Shannon Weiner diversity index, as well as a diversity index described by Cancela da Fonseca and Sarkar (1996). Differences in abundance of both the meso-and macrofauna were statistically measured using ANOVA's. Biological activity results were also interpreted using ANOV A's. Results indicate that the abundance of the meso fauna was the highest at the organically treated vineyard soil and lowest in the conventionally managed soil where pesticide application took place. The earthworms also showed the same trend as the mesofauna, but were much more influenced by seasonal changes. Biological activity, according to the bait lamina and the litter-bag results, was higher in both the conventionally and organically managed soils than in the control, but no statistical significant differences were found between the two experimental soils. The soil respiration (C02-flux), also indicating biological activity, was highest in the organically treated soil and lowest in the conventionally treated soil. The different sampling techniques used gave variable results and although the organically managed soil proved to have higher abundances of both meso- and macrofauna, the biological activity did not show the same trends. In conclusion the data did not give enough evidence as to whether organic management practices were more beneficial than conventional management practices for the maintenance of soil biodiversity.
- ItemAcclimation effects on thermal tolerance in ameronothrid mites at sub-Antarctic Marion Island(Stellenbosch : Stellenbosch University, 2005-12) Deere, Jacques Andries; Chown, S. L.; Marshall, D. J.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Evidence for widespread ecological impacts due to rapid climate change is on the increase, with further warming predicted over the next century. This increase in warming has lead to organisms adjusting their distribution range and where this is not possible organisms must cope with the stressful environments in a different way. One potential way to handle environmental stress is via a mechanism known as phenotypic plasticity, which allows an organism to express different phenotypes depending on the biotic or abiotic environment in a way that may alter that organism's fitness. Acclimation temperatures can potentially cause plastic (reversible and irreversible) changes in the response of individuals to stressful experimental conditions that could increase their survival. The issue of whether this acclimation will be beneficial to the organism or not remains contentious, with support offered both for and against the idea of beneficial acclimation. The aims of the investigation were to determine the thermal limits of five ameronothrid mite species (Halozetes marinus, H marionensis, H belgicae, H. fulvus and Podacarus auberti) from varying terrestrial habitats and to test whether there is beneficial acclimation on the thermal traits. Along with the beneficial acclimation hypothesis several alternative hypotheses were also tested. In addition, locomotor performance was determined as it has been suggested that locomotion performance is a reliable and practical measure of potential fitness of animals. The same hypotheses testing the effects of acclimation temperature on the thermal limits were tested on three performance traits; performance breadth, optimum speed and optimum temperature. Support for beneficial acclimation was found in the performance breadth and optimum speed traits for all species except for Halozetes marinus. For the optimum temperature trait the prediction for the compensation hypothesis was met and that of the beneficial acclimation hypothesis rejected, with the only exception again being that of H marinus. In the case of the locomotor performance traits the prediction for the beneficial acclimation hypothesis in the performance breadth and optimum speed traits are the same for that of the compensation hypothesis, therefore the overall response of the more terrestrial mite species is one of compensation. However, support for beneficial acclimation was not found in the thermal limit traits of all five species, with the higher acclimation temperatures (specifically 150 C) resulting in negative responses in LLT in H. marinus and H. belgicae, and in ULT in H. fulvus. Phenotypic flexibility varied between marine and terrestrial species. The less variable marine environment showed lower flexibility than that of terrestrial species in the performance breadth trait and optimum temperature trait, but there was a lack of variation between the marine and terrestrial species in the temperature tolerance traits. These results show that the effects of acclimation on various traits, especially fitness related traits, are complex and require more attention if the consequences are to be fully explained. This study therefore provides insight into the effects of acclimation on performance traits and thermal limit traits and has implications for the evolution of plastic responses in terrestrial arthropods.
- ItemAcoustic Spatial Capture-Recapture (aSCR) and the Cryptic Cape Peninsula Moss Frog Arthroleptella lightfooti(Stellenbosch : Stellenbosch University, 2018-12) Louw, Marike; Measey, John; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Quantitative measurements of wildlife populations, such as population density, are quintessential for management and conservation. Acoustic Spatial Capture-recapture (aSCR) is a technique that is used to estimate the densities of acoustically active animals. It is advantageous to use when animals defy the use of traditional methods of population estimation by being very visually cryptic, but remaining acoustically active. Arthroleptella lightfooti is a visually cryptic moss frog with an average snout to vent length of 14.5 mm. The males call during the austral winter from seepages within a restricted range across the Cape Peninsula. The species has an IUCN status of Near Threatened. Here, the population densities of the endemic A. lightfooti are estimated across their range on the Cape Peninsula for the first time using aSCR. Multiple microphones, termed “acoustic arrays”, are deployed in the field to record the calls of the frogs. I assess the use of aSCR in terms of reliability of the density estimates by examining the standard errors as coefficients of variation (CVs) of the density estimates. A density estimate with a CV above 30% was considered unreliable. Recording calls for the aSCR analyses involved visiting more than 200 sites during 2016 and 2017, and deploying acoustic arrays at a total of 149 sites, of which a subset of 85 sampling sites was used. I examined the influence of different variables on the size of the CV, namely: the average number of calls received by the acoustic array per minute, the array formation, and the detector frequencies (the combination of different numbers of microphones across which calls were heard). In addition, I made use of an output from aSCR that is an aerial view of the estimated calling locations of frogs relative to the acoustic arrays. I overlaid this output with aerial images taken at three different sites using a drone, and I examined the microhabitat features that relate most significantly to the presence of calling A. lightfooti. When there were less than 111call.min-1 received by the array, density estimates had CVs that exceeded 30% and were therefore considered unreliable. Above this threshold, 91% of density estimates were acceptable. When calls were heard on mostly one microphone, and decreasingly heard across two, three, four, five and six microphones, the density estimates were more reliable. However, when calls were mostly picked up across a combination of one and six microphones, density estimates became less reliable. This suggests that array formations should have the microphones spaced in such a way that not all calls are detected across all the microphones or only one microphone. The presence of calling frogs was significantly related to the presence of wet, seepy patches in the microhabitat and to the absence of standing water. This is consistent with observations in the field and reflects the biological needs of the species: it has no life stages in water but needs moist areas for eggs and tadpoles to develop. The successful application of aSCR to A. lightfooti is promising in the field of population studies on cryptic species, as it can be used to evaluate the populations of other calling taxa, which holds important implications for conservation and management.
- ItemAilanthus altissima : an assessment of its distribution at different spatial scales and options for management in South Africa(Stellenbosch : Stellenbosch University, 2017-03) Walker, Gareth Alexander; Richardson, D. M.; Robertson, M. P.; Gaertner, Mirijam; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: The constant flow of goods into and out of cities has resulted in the proliferation of invasive species in urban areas and, because of this, cities are viewed as ‘hotspots’ for invasive species. The rise of global trade and long distance transportation will ensure that further introductions will take place in urban ecosystems. Conditions that have been altered due to human activities enable some alien species to proliferate rapidly throughout urban centres, often also spreading into natural and semi-natural areas at the urban/wildland interface. Evaluating the current distribution of an invader by analysing potential patterns in its distribution, as well as determining the potential distribution of a species over multiple landscapes and identifying factors that promote its spread, is essential for determining the full extent of an invader. Understanding 1) where a species is; 2) where a species may spread to; and 3) the factors that promote the spread of a species are all needed to gain an understanding of the biological and biogeographical preferences that facilitate the spread of the species. This is best achieved by using a multi-scale analysis that studies all aspects of an invasive species over a variety of spatial scales. This study focusses on a notorious northern hemisphere invader - Ailanthus altissima – that, although having been introduced into South Africa in 1834, is yet to replicate similar levels of invasion success. I adopted for a multi-scale analysis of the species evaluating the current and potential distribution of the species at a global scale (Chapter 1), national scale (Chapter 2) and local scale (Chapter 3). Each chapter addresses a central aim in which a number of research questions are evaluated. In Chapter 1 I assess the biogeography, distribution, and habitat suitability of A. altissima by evaluating the current and potential distribution of the species (based on climatic suitability) at both a global scale and a national scale (in South Africa). The main conclusions of this chapter are that 1) online databases (although outdated at times) provide an accurate representation of the distribution of invasive species and should therefore be accessed. This was ascertained by cross referencing a number of online databases to evaluate whether they were largely in agreement with one another in terms of the distribution of an invader; and 2) modelling the potential distribution of an invasive species based on climatic suitability serves as a good first approximation of potential species spread. Although this may be true, it was also suggested in this chapter that to accurately quantify the potential distribution of an invasive species, other distribution drivers (such as land use and human mediated disturbances) need to be incorporated into the design of a species distribution model. Chapter 2 evaluates the degree of range filling exhibited by A. altissima in South Africa and identifies areas at risk of future invasion. This chapter also identifies specific factors that promote the spread of the species at a global and national scale. I determined that at the global scale, climate had the highest influence on the distribution of A. altissima whereas at the national scale, human mediated disturbances exerted a higher influence on the distribution of the species. This chapter builds on the concepts proposed in Chapter 1 by highlighting the importance of incorporating different environmental variables at various spatial scales to identify potential invasion ‘hotspots’. I conclude that the multi-scale approach presented in this chapter enables the early detection of invasive species, preventing damage associate with their potential spread. Also, the novelty of this approach is particularly effective when it comes to analysing urban invaders. The third chapter evaluates the distribution pattern of A. altissima within the City of Cape Town by using the suburb of Newlands as a case study. In addition, it determines potential options for management at a city scale. It can be concluded that fine-scale analysis of invasive species distributions is best achieved using Geographic Information System (GIS) techniques and that such these ultimately help to identify potential areas susceptible to future invasion while delimiting unsuitable areas. I determined that A. altissima has a preference for affluent urban areas with podzolic soils that are exposed to high levels of rainfall within the City of Cape Town. Using this information, I determined that there is a large capacity for further spread by the species throughout the city. The systematic approach that we used in Newlands is an effective way of gauging the full extent of an invader and is especially effective for evaluating the population structure of a particular invasive species. Future studies should adopt this approach in conjunction with remote sensing techniques to achieve the best possible results. The final chapter of this thesis provides the overall conclusions in which all the main findings are highlighted. Altogether, the approach presented in this thesis is an effective method that could be used on other emerging, urban invaders globally. The systematic, multi-scale analysis proposed in this project showed high levels of success and it is my belief that this project achieved its desired aims.
- ItemThe alarm vocalizations of Brants' whistling rat, Parotomys Brantsii(Stellenbosch : Stellenbosch University, 2001-12) Le Roux, Aliza; Cherry, M. I.; Jackson, T. P.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: The alarm calls of a colonial rodent, Brants' whistling rat (Parotomys brantsii), were investigated at Goegap Nature Reserve in the Northern Cape, South Africa. At this site P. brantsii occurs in sympatry with the congeneric P. littledalei, and the alarm calls in response to humans was compared between the two species. Parotomys brantsii's typical call in reaction to a human is a simple whistle, characterized by an initial upward frequency sweep and high frequency plateau, whereas the alarm whistle of P. littledalei has three overlapping components. Parotomys littledalei's calls are significantly shorter and lower in dominant frequency than those of P. brantsii, and have a significantly wider frequency bandwidth. These distinctions were attributed to species discrimination and habitat preferences. The acoustic adaptation hypothesis is supported in part, as P. littledalei, which inhabits a closed habitat in comparison with P. brantsii, has calls which are lower in frequency than P. brantsii calls, but contrary to the hypothesis, P. brantsii calls show less frequency modulation than those of P. littledalei. The high pitch of both species' vocalizations may be a convergent feature making the callers difficult for predators to locate. The alarm call repertoire of P. brantsii was investigated by presenting members of the P. brantsii colony with models of some typical predators, a raptor and puff adder, as well as a human observer. Virtually no variation was detected in the structure of alarm whistles elicited by different predators, indicating that P. brantsii did not identify different predator types by means of vocalizations, even though behavioural responses showed that P. brantsii do distinguish between different predators and non-predators. Note duration varied in conjunction with the physical reaction of the caller. When the caller bolted towards safety, the whistle was significantly shorter than when it remained aboveground. During an encounter with a snake or far-off human the caller would utter relatively long duration calls, signifying a low-risk situation, while highrisk situations such as a nearby human or raptor provoked short calls, emitted just before the whistling rat bolted underground. I regard P. brantsii's alarm call repertoire as a graded "urgency-based" system, indicating threat level perceived rather than predator type. This system is widespread among ground squirrels and is usually associated with animals inhabiting a two-dimensional environment. Playback experiments were conducted to determine the meaning of alarm calls to conspecifics, focusing specifically on the effect of variation in single call duration and function of alarm-calling bouts. All alarm calls induced heightened vigilance in receivers, but the behavioural response did not differ between short and long single calls. Multiple calls lead to significantly longer periods of high vigilance than single calls even after calling bouts have ended, showing that one of the functions of multiple calls is to maintain high vigilance in conspecifics for relatively long periods. The non-iconic nature of their alarm calls and the undiscriminating response of receivers to different calls emphasizes the importance of contextual clues in the communication system of animals living in an open habitat like that of P. brantsii.
- ItemAlien species and propagules in the Antarctic : movements through space and time(Stellenbosch : University of Stellenbosch, 2009-03) Lee, Jennifer Elizabeth; Chown, Steven L.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Although the impacts of biological invasions are widely appreciated, a bias exists in research effort to post‐dispersal processes because of the difficulties of measuring propagule pressure and the detecting of newly established species. Here the Antarctic is used as a model system in which to quantify the initial dispersal of alien species and investigate the factors that contribute to the establishment and range dynamics of alien species once they have arrived in the region. Human movements are known to transport alien species into the Antarctic, some of which have successfully established and had wide ranging consequences in recipient ecosystems. Considering terrestrial flora, this research found that over 700 seeds from 99 taxa, including some species known to be invasive, are transported into the Antarctic each year in association with South African National Antarctic Programme (SANAP) passenger luggage and cargo. The first ever assessment of propagule drop‐off indicated that 30‐50% of these propagules will enter the recipient environment. Further results suggested that the construction of the British Antarctic Survey Halley VI station will facilitate the transport of over 5000 seeds from 34 taxa into the region, making this a significant pathway for introductions. Propagule pressure due to SANAP logistics is also considerable for marine species. Fouling assemblages on the external hull surfaces of the SANAP resupply vessel, the SA Agulhas, form only once the vessel’s anti‐fouling paint has been damaged by travel through sea ice and are characterised by low diversity. Ice scour prevents fouling assemblages from being transported to the Antarctic continent, but assemblages remain largely intact when travelling to sub‐Antarctic Islands. In the sea‐chests of the vessel populations of a known invasive, Mytilus galloprovincialis, were found with some individuals having survived transportation to the Antarctic region on multiple occasions. Once species have overcome initial dispersal barriers, they face further ecological and physiological challenges in order to establish in the recipient region. The parasitoid wasp Aphidius matricariae was first recorded on Marion Island in 2001. Surveys around the island show that adult abundance and the frequency of aphid parasitism are highest adjacent to a common anchor point of the SA Agulhas and decline away from this region. Genetic diversity was low, suggesting that the population was established from a single introduction. This highlights that high propagule pressure is not necessary for successful establishment of introduced invertebrates. Another species that has overcome the dispersal barrier is the terrestrial slug Deroceras panormitanum, which was introduced to Marion Island in the 1970’s and has since spread throughout much of the coastal habitat of the island. For this species range limits are set by intolerance of low temperature and salinity, and abundance structure is characterized by patches and gaps which are associated with this species inability to tolerate dry conditions. To prevent further alien introductions in the region, targeted management of high risk pathways is required. In addition, increased vigilance is needed to detect and manage newly established aliens before their ranges expand.
- ItemAmphibian conservation in an urban park : a spatial approach to quantifying threats to Anura on the Cape peninsula(Stellenbosch : Stellenbosch University, 2017-12) Ebrahim, Zishan Cassiem; Measey, G. J.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Species’ threat assessments produce generalized threat impact scores, often by considering regional-scale representations of threats. Cities, on the other hand, produce municipal-scale, high resolution data that are proxies for threats; furthermore, cities in mega-diverse regions are home to a high number of threatened species. Prioritization of conservation action is biased for where more information is known (about the ecosystem), and where a positive outcome can be anticipated. Eight Cape peninsula amphibian species have a threatened conservation status. They are isolated on highlands or are restricted to remnant and suburban habitats, dependent on both urban and protected terrestrial and freshwater habitats found in the City of Cape Town and Table Mountain National Park. In Chapter Two, I used spatial data (shapefiles) to represent threats in a Geographic Information System to spatially define threats to eight amphibian species (five lowland, three upland). I used two approaches: weighted and un-weighted by a threat impact-score, to produce five indices of local threats. The Micro Frog (Microbatrachella capensis) is assessed as the most threatened peninsula frog species by three of the five indices considered. The results show that for lowland species, the threat-class of greatest extent is ‘Residential and commercial development’. The three lowland species most exposed to this threat are M. capensis (100% exposed to potential development), Breviceps gibbosus (55.6% of its 8.5 km2 putative peninsula distribution), and Sclerophrys pantherina (38.4% of its 199.7 km2 distribution). The Compounded and the General Threat Index correlate to the (global) Redlist Index (P < 0.05); but no correlation to the regional Red Listing, indicating congruency of threats and threat status. The Critically Endangered Table Mountain Ghost Frog (Heleophryne rosei) is torrent adapted, and found only on the Table Mountain massif. CapeNature monitors tadpoles, and SANParks monitors (selected) stream parameters. In Chapter Three, I analyse water-habitat monitoring data (controlled for altitude) to show where threats of habitat alteration, drought, or temperature extremes may affect the H. rosei metapopulation. Permanence of water-flow and water temperature are shown to be very highly significant predictors of tadpole presence (p = 0.0005, r = 0.78). The lower the water temperature, the more likely tadpoles are present. Streams with a mean summer temperature greater than 17.2°C (n=3) at 400 to 300 meters above sea level were found to have no tadpoles at this altitude. Permanence of water flow is significant, as tadpoles need more than one year to reach metamorphosis. Summer water temperatures over an average of 17.2°C should be a red-flag for management authorities responsible for bulk-water supply, threat mitigation efforts, and biodiversity conservation. Spatial indices of threat are useful to illustrate the relative exposure to threats at a local (city) scale. Threats to different lowland amphibians are similar (e.g. residential and commercial development), which varies from the mutual threats to different upland amphibians. Fundamental to stream species’ conservation is water supply and demand management, while upland terrestrial species are most affected by veld age and invasive alien flora. Some threats are common for both areas (e.g. invasive alien species). Key words: Threat impact score, threatened areas, GIS, habitat loss, amphibians, Table Mountain National Park, Cape Town, environmental water requirement, water temperature, habitat.
- ItemAn analysis of the Cordylus Polyzonus complex (Reptilia : Cordylidae) in the South-Western Cape(Stellenbosch : University of Stellenbosch, 1990-03) Badenhorst, N. C.; Mouton, P. le F. N.; Van Wyk, J. H.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.Mouton and Oelofsen (1988) suggested that melanistic cordylid populations in the southwestern Cape represent relict, cold-adapted populations which evolved under adverse climatic conditions during the Last Glacial Period, 18000-16000 BP. The first section of this study was undertaken to test their model for the evolution of melanism in the cordylid species, Cordylus polyzonus. For this purpose, geographic character variation among populations of Cordylus polyzonus in the region south of 32°15' latitude and west of 19015' longitude was investigated. Variation in 122 external morphological characters was analysed in 306 specimens from 93 localities. Although no inter-locality variation was observed in most of the characters, a high degree of concordancy was observed in the geographical variation of three headshield characters. These three headshield characters are considered non-adaptive and can accordingly be regarded as good indicators of genealogical relationship. Since they varied together with other adaptive characters such as melanism and body size, it can be concluded that geographically isolated melanistic populations of Cordylus polyzonus represent relicts of a once larger melanistic population. The data underscore the Mouton-Oelofsen hypothesis for the evolution of melanistic cordylid taxa in the south-western Cape. A further corrolary of the Mouton-Oelofsen hypothesis, is that melanistic cordylids are presently restricted to cool enclaves. This assumption was evaluated in the second section of this study by analysing prevailing climatic conditions associated with the occurrence of extant melanistic populations of the genera Cordylus and Pseudocordylus in the southwestern Cape. Climatic data were obtained from 123 weather stations in the study-area. A close correspondence was found between the distribution of melanistic populations along the westcoast and the primary upwelling zones of the southern Benguela Current. Lower mean daily temperatures and a high incidence of advective sea fog on the adjacent coastal regions are direct effects of these cold upwelled waters. Likewise, montane melanistic populations, occurring at relatively high altitudes along the extreme western borders of the Cape Fold Mountains, also experience lower mean daily temperatures and a high incidence of orographic fog and cloud cover. Melanistic cordylid populations therefore generally have to 4. contend with relatively exposed environmental conditions of low temperature and limited solar radiation due to the filtering effect of fog and cloud cover. The fact that all the melanistic taxa in this region occur as small isolated populations limited to cool enclaves, suggests that they are presently in a contracted state under strong environmental pressure. It is postulated that palaeoclimatic conditions very similar to climatic conditions presently prevailing in these enclaves were experienced over the entire western coastal region, at least as far as the Orange River, during the Last Glacial Maximum when melanism probably evolved. Our results therefore corroborate the Mouton-Oelofsen hypothesis that isolated melanistic cordylid populations represent cold-adapted relicts. One would accordingly expect melanistic populations to posses some enhanced ability to absorb infrared radiant heat to cope with these conditions of limited sunshine and lower temperatures. In section three of this study, differences in dorsal skin reflectivity between melanistic and turquoise ~. polyzonus populations were quantified. Furthermore, the physiological ability of this species to change body colour was investigated, as well as ontogenetic colour change. Significant differences in dorsal skin reflectivity existed between melanistic and turquoise specimens in the 500-1300 mjl spectral range, demonstrating the greater heat-absorbing capacity of melanistic populations. The data underscore the MoutonOelofsen model that melanistic populations are "cold-adapted" relicts. Furthermore, ontogenetic colour change is a real phenomenon in the melanistic variation of C. polyzonus. In this respect it is unique among the melanistic cordylid taxa in that ontogenetic colour change seemingly does not occur in the other forms. Experiments to investigate short term colour change in response to different temperatures regimes, produced no conclusive results. On the other hand, seasonal colour changes could be demonstrated for both melanistic and turquoise specimens, indicating that this species has the physiological capacity to change colour. It is, however, believed that geographic colour variation in ~. polyzonus cannot be attributed to this capacity, but is rather the result of selection over time. This view is underscored by the results of section one demonstrating that, apart from colour and body size, melanistic and turquoise forms also differ in certain non-adaptive traits; suggesting that they do not belong to the same primary gene pool.
- ItemAn analysis of the Pseudocordylus melanotus complex (Sauria: Cordylidae)(Stellenbosch : Stellenbosch University, 2007-04) Bates, Michael Francis; Mouton, P. le F. N.; Branch, W. R.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: The taxonomic status of southern Africa’s rupicolous crag lizards (genus Pseudocordylus) was investigated. As considerable confusion exists in the literature regarding the type specimens and type localities of the various taxa, resolution of these problems were considered the starting point of the study. Examination of museum specimens allowed for the designation of lectotypes, alloparalectotypes and/or paralectotypes. Of particular relevance to this study was the rediscovery of Andrew Smith’s type specimens of P. m. melanotus and P. m. subviridis. Restriction of the type locality of P. m. subviridis, based on entries in Smith’s diary and journal, allowed for the confirmation of previous interpretations and definitions of the two taxa. The geographical distribution of the various taxa and populations was determined using an extensive locality database. Two kinds of molecular markers, namely allozymes and mitochondrial DNA, were used in an attempt to resolve taxon boundaries within the P. melanotus species complex. The allozyme analysis indicated that P. m. melanotus might be polyphyletic and comprised of two unrelated lineages. Furthermore, fixed allelic differences between parapatric populations of P. m. melanotus and P. m. subviridis, and between sympatric populations of P. m. subviridis and P. langi, suggested that all three forms might be considered full species, with the possibility of more cryptic species present in the complex. Pseudocordylus transvaalensis differed from most other populations by 1-3 fixed allelic differences, but was indistinguishable from the Nkandhla district (central KwaZulu-Natal) population of P. m. melanotus. There were no heterozygous individuals in a sample from Monontsha Pass (Qwa-Qwa), a population reportedly comprising P. m. melanotus and P. m. subviridis, as well as intermediates, and all specimens were assignable to P. m. subviridis. The allozyme study was, however, based on phenetic principles and for further taxonomic resolution a cladistic approach was required. An mtDNA analysis (16S rRNA gene) using Maximum Parsimony, Maximum Likelihood and Bayesian analyses was therefore conducted to determine phylogenetic relationships among species and subspecies and to re-assess the taxonomic status of forms in the P. melanotus species complex. The mtDNA analysis corroborated most of the results obtained in the allozyme analysis. Firstly, P. langi was again found to be basal. With the addition of P. microlepidotus and P. spinosus to the ingroup, it is now apparent that P. langi is the basal species in the genus. (Recent studies have indicated that P. capensis and P. nebulosus are not congeneric with Pseudocordylus.) Secondly, the 16S rRNA results confirm that P. m. melanotus, as presently construed, is comprised of two clades that are not sister groups. The northern populations of P. m. melanotus (Sabie and Lochiel) form a fairly deeply divergent clade that may represent a separate species. The Nkandla population was, however, found to cluster with the other southern P. m. melanotus populations and not with P. transvaalensis as was the case in the allozyme electrophoretic analysis. However, the most surprising result of the 16S rRNA analysis was the finding that both P. microlepidotus and P. spinosus are embedded within P. m. subviridis. This suggests that these two species evolved from within P. m. subviridis and may have been separated only recently, with rapid morphological divergence occurring, but with limited genetic differentiation. It is suggested that all of the above three taxa be provisionally treated as full species. There was also morphological support for the uniqueness of all groupings indicated by the mtDNA analysis. Pseudocordylus transvaalensis is characterized by its large size, unique dorsal and gular (black) colour patterns, as many as three horizontal rows of lateral temporal scales, a series of small scales posterior to the interparietal scale, and usually two subocular scales behind the median subocular on either side of the head. The various populations currently classified under the name P. melanotus are more difficult to separate, but P. m. melanotus and P. m. subviridis usually differ as follows: frontonasal divided in P. m. melanotus, undivided in P. m. subviridis (and most Northern melanotus); lateral temporals in two rows, upper more elongate versus single row of much elongated scales; longitudinal rows of dorsolaterals closely-set versus widely separated; femoral pores of females pit-like versus deep with secretory plug. Northern melanotus differs from Southern melanotus in usually having an undivided frontonasal scale and seldom having a small scale present behind the frontonasal. Pseudocordylus langi has unique dorsal and gular colour patterns (including a series of blue spots on the flanks), granular dorsals with 6-9 paravertebral rows of enlarged flat scales, high total numbers of femoral pores (25-34) and usually only five (smooth not keeled or ridged) infralabial scales on either side of the head. Pseudocordylus spinosus also has unique dorsal and gular colour patterns, spinose lateral scales, frontonasal longer than wide and excluded from the loreal scales, low total femoral pore counts (6-9), and females (not only males) have differentiated femoral scales. Both Principal Components Analysis (PCA) and Canonical Discriminant Analysis (CDA) distinguished four groups, namely P. transvaalensis, P. langi, P. spinosus and a P. melanotus/subviridis/microlepidotus cluster. A separate CDA of all P. melanotus populations partly distinguished between Southern melanotus and P. m. subviridis, and largely separated Northern melanotus; whereas a CDA of P. transvaalensis showed that all three allopatric populations are 100% distinguishable in morphological space. A Nested Clade Analysis indicated that fragmentation as well as range expansion played a role in the distribution of the P. melanotus species complex. This may be explained by climatic oscillations (high-low temperatures and wet-dry cycles) during the Cenozoic that caused habitat expansion and contraction. Based on the topology of the mtDNA phylogram it is apparent that the genus Pseudocordylus originated along the eastern escarpment. A P. langi-like ancestor may have had an extensive range along the eastern escarpment, with the Maloti-Drakensberg forming the southern limit of its range. During a subsequent rise in global temperatures, range contraction and fragmentation took place, leaving an isolated population in the south and one in the north. The southern population survived unchanged in the Maloti-Drakensberg refugium, but the northern population was forced to adapt to the warmer conditions. Thereafter, the northern form expanded its range again, but during a subsequent cooler period, range contraction occurred, resulting in an isolated north-eastern population in the Sabie-Lochiel area in Mpumulanga (Northern melanotus) and a western population. Relationships in the latter clade are not sufficiently resolved to allow further reconstruction of biogeographic history, but it is clear that a P. m. subviridis-like form became isolated in the south where it eventually came into contact with P. langi at high elevations. Pseudocordylus m. subviridis eventually extended its range southwestwards into the inland mountains of the Eastern Cape and Cape Fold Mountains to give rise to the P. microlepidotus complex. This cycle of range expansion and contraction may also account for the isolated populations at Suikerbosrand, Nkandhla district, and in the Amatole-Great Winterberg mountain region. Furthermore, it is suggested that P. spinosus originated from a P. m. subviridis-like ancestral population that became isolated on the lower slopes of the Drakensberg where terrestrial predation pressure resulted in a quick shift in morphology from fairly smooth body scales to a more spiny morphology.
- ItemAn anatomical and systematic study of the family Mesosauridae (reptilia : proganosauria) with special reference to its associated fauna and palaeoecological environment in the Whitehill Sea(Stellenbosch : Stellenbosch University, 1900) Oelofsen, B. W.(Burger Wilhelm); Stellenbosch University. Faculty of Science. Department of Botany & Zoology.ENGLISH ABSTRACT: The anatomy and taxonomy of the southern African fossil reptile Mesosaurus from the Whitehill Shale has shown that the Formation is a chronostratigraphic unit. It is postulated that the almost identical Whitehill and Iraty Formations were deposited in shallow contemporaneous embayments of a central sea arm that occupied a position between the two continents. The water body was stratefied with anoxic, toxic, bottom brines that prevented the establishment of a benthonic fauna. A Study of the newly collected fossil material led to a new interpretation of the cranial morphology of Mesosaurus and it was found to be anapsid and closely allied to Limnoscelis. If M.tenuidens is to be regarded as typical for the Mesosauridae, all the members of the order Proganosauria will have to be transferred to the order Cotylosauria. M. tenuids was found to differ from M.brasiliensis and is the only species of Mesosaurus in the southern African Permo-Carboniferous Whitehill Formation. Along with it two more forms, noteosaurus africanus Broom and a yet unidentified species, identical with or closely allied to Stereosternum tumidum occur.
- ItemAnatomical survey of the formation of primary xylem and nutrients supply to the reproductive apple bud(Stellenbosch : Stellebosch University, 2017-03) Frazenburg, Madelaine; Dreyer, L. L.; Lotze, Elmi; Turketti, S. S.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Apple (Malus domestica Borkh.) is a deciduous fruit species, which is subject to dormancy before bud break occurs in spring. Although not noticed externally, anatomical changes occur in the reproductive bud during this dormant period, including formation of the carpels, enlargement of the petals and carpel and anther elongation. In this study, we determined i) the time of primary xylem formation as influenced by cultivar, month and/or climate (expressed by winter chilling) and ii) the distribution and quantification of a selected nutrient calcium (Ca) in, (a) the primary xylem tissue as well as (b) in reserve tissues (spur, leaf and apical meristem). Four different commercial apple cultivars were selected for this investigation. Golden Delicious and Braeburn represented cultivars with typical Ca deficiency symptoms in the fruit if additional Ca is not applied, whereas Royal Gala and Cripps Pink represented cultivars in which Ca related problems occur less frequently. Golden Delicious and Royal Gala are cultivars associated with high chilling requirements, and Braeburn and Cripps Pink, with medium chilling requirements. Sampling of dormant buds occurred during June, July, August and September in 2012, 2014 and 2015. The different cultivars used for this investigation were cultivated in Stellenbosch and Elgin. Although these regions are both in the Western Cape Province, the Elgin region is an area with a higher chill unit accumulation than Stellenbosch. Light, fluorescence and scanning electron microscopy imaging techniques were used to study the anatomy of primary xylem development. To differentiate the degree of lignification in primary xylem from secondary xylem, samples were imaged with a Zeiss LSM880 confocal microscope equipped with ZEN 2 software. Scanning electron microscopy images were acquired using a Zeiss Merlin FEG Scanning Electron Microscope (SEM). After the time (month) of primary xylem establishment in the bud was identified, Ca concentration (%) was quantified in reproductive apple bud tissues of all four cultivars during three seasons (2012, 2014 and 2015). Ca concentration was quantified with Wavelength Dispersive Spectrometer (Oxford Instrument® Wave Dispersive X-ray Spectrometer). Ca was simultaneously quantified with Electron Dispersive X-ray (Oxford Instrument ® Energy Dispersive X-ray). In Golden Delicious and Braeburn, the process of secondary xylem development commenced earlier than in Cripps Pink and Royal Gala. While this process is slow in Cripps Pink, xylem development proceeds much faster in Royal Gala and changes from having only primary xylem in July to having secondary xylem a month later. The timing and duration of xylem development in Cripps Pink and Royal Gala were similar in the Stellenbosch and Elgin regions in June, but differed in July and August in all three seasons. Results clearly show differences in Ca distribution and Ca concentration in the tissues of dormant reproductive apple buds of the four cultivars studied. High Ca levels were noted in the spur transport tissue of Royal Gala, Cripps Pink and Braeburn during June, with considerably lower levels of Ca in the same region in Golden Delicious. Cripps Pink and Royal Gala have a higher Ca concentration in the xylem in June, followed by an increase in Ca concentration towards September. The reduction in Ca concentration in the spur during the same period may indicate that reserve Ca from the spur is allocated towards the xylem. This needs further investigation. Although trends were not as clear in Golden Delicious and Braeburn and did not always follow the same pattern, observations in these cultivars differed from those in Cripps Pink and Royal Gala, confirming the higher presence of primary xylem reported previously. Thus, later formation or presence of primary xylem in the dormant bud of these cultivars may partly explain the lower Ca concentrations and difference in Ca distribution between tissues compared to Cripps Pink and Braeburn.
- Itemn Anatomiese studie van Vitis-wortels, gesond en beskadig deur Filloksera(Stellenbosch : Stellenbosch University, 1968-03) Britz, C. J.; De Vos, M. P.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.Please refer to full text for abstract
- ItemAndrogen controlled secondary sexual characters in the male African clawed frog, Xenopus laevis, as potential biomarkers for endocrine disruptor contaminants (with special reference to fungicides) in aquatic systems(Stellenbosch : Stellenbosch University, 2014-04) Archer, Edward; van Wyk, Johannes, Hendrik; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Endocrine disrupting contaminants (EDCs) coming from households, industrial parks, wastewater (sewage) treatment and agricultural areas have been shown to pollute our freshwater systems. These contaminants may disrupt early development and reproductive systems in freshwater organisms (fish, frogs and crocodile species) as well as humans. Agricultural pesticides are shown as a large contributor to endocrine disruption activity in water catchment areas through spray drift, runoff, and/or groundwater leeching. Although South Africa is recognized as the largest consumer of agricultural pesticides in Africa, few studies have been undertaken to assess the prevalence and impact of endocrine disorders activities of pesticides in local freshwater systems. Recent studies have suggested that various agricultural pesticides, especially fungicides, might have adverse effects on the male endocrine system. There is therefore a need to test for a wider range of endocrine disrupting activities (mechanisms) in environmental waters other than conventional estrogenic (feminising) activities. Furthermore, there is a need to establish biomarkers in endemic species (bio-indicators) to show endocrine disruption in vertebrates (therefore also apply to humans). The specific objectives of the study were to: (1) describe and confirm the use of androgen-controlled breeding glands in male African clawed frogs (Xenopus laevis) as a biomarker for (anti)androgenic endocrine disruption activity (Chapter 2), (2) to investigate the premature development of breeding glands in X. laevis tadpoles (pre-metamorphic) and young froglets (post-metamorphic) (Chapter 2), (3) to investigate the disruption of male reproductive traits in adult X. laevis frogs by exposure to substances disrupting two different anti-androgenic endocrine disruption pathways (Chapter 3), (4) screen for (anti)androgenic activity of individual and binary mixtures of pesticides, which are regularly used in agricultural areas in the Western Cape Province of South Africa (Chapter 4), and (5) to test for (anti)androgenic and estrogenic endocrine disrupting activities by making use of in vitro assays as well as adult male X. laevis frogs collected from selected ponds surrounded by vineyards and fruit orchards in the Stellenbosch Winelands. The present study confirmed that male breeding glands can serve as biomarkers for (anti)androgenic endocrine disruption and that male reproductive and secondary sexual characteristics can be disrupted through two different biochemical control pathways. The study also confirmed that the expression of androgen-regulated breeding glands can be stimulated in pre-metamorphic tadpoles and immature, post-metamorphic frogs, and can thus be used for (anti)androgenic testing. The rapid testing and predictive value of an in vitro recombinant yeast screen for androgen receptor binding inhibition of selected individual or binary mixtures of pesticides was also confirmed. However, the current study showed that the predicted in vitro (anti)androgenic activity did not always correspond with in vivo (anti)androgenic biomarker outcomes. This It also confirmed that single-cell in vitro assays can be used as a first-level prediction for (anti)androgenic activities of individual or mixtures of agricultural pesticides. This study provides a better understanding for potential mixture interactions of commonly used agricultural pesticides, the hormonal control of secondary sexual characteristics in male frogs and the use of reproduction biomarkers to study long-term effects of endocrine disruptors in local water supplies.
- ItemThe antimicrobial interactions of Agathosma crenulata, Dodonaea viscosa and Eucalyptus globulus combination and their chemical profiling(Stellenbosch : Stellenbosch University, 2013-12) Zonyane, Samkele; Makunga, N. P.; Van Vuuren, S. F.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: In traditional medicine, there is a long-standing culture of combining herbal drugs to increase the therapeutic efficacy. The improved medical action is thought to be due to synergistic interactions between different plant bioactive components. The aim of this study was to test the pharmacological interactions in a medicinal plant combination which consisted of Agathosma crenulata, Dodonaea viscosa and Eucalyptus globulus. The rationale for the analysis of this particular mixture is that it had noteworthy antibacterial activity and exhibited the highest activity out of seven medicinal plant mixtures previously investigated. Using chromatographic analysis, the phytochemistry of the plants was also assessed. The chloroform: methanol (1:1; v/v) extracts or hydo-distilled essential oils (A. crenulata and E. globulus) were screened individually and in combinations (double and triple plant combination) for activity against five respiratory pathogens using a microdilution assay. The antimicrobial interactions in combinations were assessed with the fractional inhibitory concentration (FIC) and the isobolograms. The organic extracts generally showed the highest antimicrobial activity with E. globulus having the highest activity with MIC values below 1 mg ml-1 representing noteworthy activity. The overall activity of the aqueous extracts was poor. The essential oil activity of E. globulus was mostly noteworthy (0.5 to 2 mg ml-1) while A. crenulata essential oil displayed moderate activity (1 to 4 mg ml-1). The ΣFIC values for double combinations (1:1) of A. crenulata with D. viscosa, A. crenulata with E. globulus and D. viscosa with E. globulus were calculated from the minimum inhibitory concentration (MIC) data and the interactions were classified as synergistic, additive, indifferent and antagonistic. The highest synergistic interactions observed were for a 1:1 combination of A. crenulata with E. globulus against K. pneumoniae, S. aureus and B. subtilis with ΣFIC values of 0.07. There was only one incident of antagonism noted in the study for D. viscosa with E. globulus (1:1) against C. neoformans with ΣFIC value of 4.25. The double combinations against selective pathogens (K. pneumoniae, S. aureus and E. coli) were further analysed for interactions using isobolograms. Mostly, the antimicrobial interactions as presented by the isobolograms were congruent with FIC results which further validated the occurrence of relevant antimicrobial interactions in those combinations. The ΣFIC values for triple combinations (1:1:1) revealed mostly synergistic interactions. When the triple combinations were analysed further against certain pathogens based on the predictions of the Design of Experiments software program (MODDE 9.1®), the MIC values remained the same despite the different combinations that were tested Thin layer chromatography (TLC) was used for a quick chemical fingerprinting of the plant extracts. This was followed by a bio-autographic assay. The chemical profiles of the organic extracts and essential oils from two of the study aromatic plants (A. crenulata and E. globulus) were further analysed with liquid chromatography mass spectrometry (LC-MS) and gas chromatography mass spectrometry (GC-MS) respectively. For combined plant extracts, a multivariate data analysis using principal component analysis (PCA) and hierarchical clustering analysis (HCA) was used to determine the relationship of the chemical make-up of combinations with that of individual plant extracts. According to the TLC analysis, E. globulus extracts had more compounds than the other two plants in the study. For the bio-autographic assay, E. globulus and combinations that included this plant showed greater inhibition zones than A. crenulata and D. viscosa. For the LC-MS analysis, PCA and HCA showed a close relationship between A. crenulata with D. viscosa, D. viscosa with E. globulus and the triple combination. Twenty one components were identified in the essential oil of A. crenulata representing 88.83% of the total oil composition. The oil was dominated by oxygen-containing monoterpenes (46.25%). In the essential oil of E. globulus, twenty six compounds were identified making up to 95.62% of the oil composition. Oxygen-containing monoterpenes (32.98%) also dominated the E. globulus essential oil. There was no great variation in essential oil metabolites of the individual plants and their combination as shown by both PCA and HCA. The enhanced in vitro antimicrobial activity and pharmacological interactions (synergy and additivity) in some of the combinations (double and triple) that were tested in this study adds scientific support to the use of medicinal plant combinations in Western Cape traditional medicine. The metabolic profiles of plants in combination might be unique due to interaction of the different plant bioactive molecules and thus result into defined antimicrobial activity.
- ItemAspects of ecosystem function in a woodland savanna in South West Africa(Stellenbosch : Stellenbosch University, 1975-12) Rutherford, Michael Charles; Smith, J. G.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: A study was made of certain relations operating within a South West African woodland savanna ecosystem which was characterised by simplification within most of its basic components. . Main attention was given to the relatively unexplored field of spatial and structural organisation of the primary producer component in relation to its quantified intra-seasonal functional changes including its phenology. Simple mathematical model descriptions of seasonal mass change of the herbaceous parts of the primary producer component were derived. Various parts of the primary producer component were also evaluated in terms of some of the main climatic driving forces of the ecosystem, decomposition relations in the form of disappearance rates, soil-vegetation mineral relations and consumer (mainly insect) relations. Gross effects of manipulation of the ecosystem type by fire and management is included.
- ItemAspects of the thermal ecology of the group-living lizard, Cordylus cataphractus : a spatial and temporal analysis(Stellenbosch : University of Stellenbosch, 2011-03) Truter, Johannes Christoff; Van Wyk, Johannes H.; Mouton, P. le Fras N.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Thermal ecology is a central theme in reptilian biology because of the thermodynamic rate dependence of virtually all biological processes in these ectothermic animals. Thermoregulation includes active processes (with associated energetic costs related to altered behaviour and physiology) functioning to maintain body temperatures within a preferred temperature range, so that the majority of physiological functions occurs optimally, despite natural variation in the animal’s thermal habitat. The recent development of quantitative thermal indices now allows researchers to describe the thermal habitat and thermoregulatory functioning of an ectotherm within its environment from a cost-benefit perspective. The use of such quantitative biophysical approaches to reptile thermal ecology studies is however limited in the African context. Cordylus cataphractus is one of the best studied cordylids, and exhibits various characteristics atypical for the family, such as permanent group-living, seasonally lowered surface activity, a low resting metabolic rate and large fat bodies. These characteristics are generally thought to be associated with groupliving in a semi-arid habitat, yet, the possible links to thermal ecology remains unexplored. The objectives of the current study was: firstly, to characterize the preferred temperature range (Tp) of C. cataphractus through the use of ecologically realistic laboratory thermal gradients; secondly, to explore seasonal and geographical variation in thermal preference, by comparing Tp among individuals captured from a coastal and inland population and during different seasons (autumn and spring); thirdly, to describe the thermal habitat of a C. cataphractus population during summer, autumn, winter and spring and to then relate these findings to the seasonal activity patterns reported in literature for the species; fourthly, to describe the seasonal patterns of thermoregulation (during summer, autumn, winter and spring) in a C. cataphractus population through quantitative thermoregulatory indices; fifthly, to assess geographic variation in the thermal habitat and IV associated patterns of thermoregulation in C. cataphractus among a coastal population (western range limit) and an inland population (eastern range limit). The thermal habitat of C. cataphractus was described by measuring operative environmental temperatures (Te) with hollow copper lizard models placed around rocks according to the natural surface movement patterns of the species. Variation in thermal habitat quality was subsequently calculated (de = |Te – Tp|) and averaged. Field body temperatures (Tb) of lizards were measured with dorsally attached miniature temperature loggers. Thermoregulatory indices were calculated from Te, Tb and Tp, describing: thermoregulatory accuracy, the effectiveness of thermoregulation and thermal exploitation for each population (coastal and inland) for the respective sampling periods. The preferred body temperature range of C. cataphractus is the lowest recorded among cordylids to date (mean Tp = 29.8oC) and was conserved among different populations and within these populations among seasons, despite the fact that environmental temperatures are known to vary geographically and seasonally. Thermal habitat quality varied significantly at micro spatial scale around rocks in the coastal population. Since C. cataphractus males are territorial, competition for thermal habitat quality around rocks may therefore occur. Such effects will be a function of the time of year since the variability in thermal habitat quality among rock aspects (around rocks) varied seasonally. Thermal habitat quality of crevices varied among seasons and was typically higher in the open, outside rock crevices, during the cooler winter and spring periods, whereas in summer and autumn the crevice environments were more favourable. Thermal habitat quality was high in crevices during autumn, suggesting that the observed repressed surface activity of C. cataphractus described for the time is not necessarily, as previously thought, only due to food constraints. Moreover, in contrast to earlier reports, the current results (Tb versus Te) indicate that individuals emerged from crevices in summer. The geographical assessment indicated that lizards from the coastal population, with generally larger groups, thermoregulated more successfully than those from the inland population. The higher thermoregulatory success in the coastal population occurred in spite of the fact that thermal habitat quality was significantly lower at the coastal locality. The higher thermoregulatory success in the coastal population was likely due to reduced predation risk associated with increased group-size. The seasonal trends in thermoregulation at the coastal and inland population corresponded to the patterns predicted by the cost-benefit model of thermoregulation, accuracy of thermoregulation and the effectiveness of thermal exploitation being higher during the thermally more favourable autumn.
- ItemAspekte van die ekofisiologie van die halofiet Triglochin bulbosa L.(Stellenbosch : Stellenbosch University, 1990-03) Becker, Theresa; Jooste, J. H.; Stellenbosch University. Faculty of Science. Department of Botany and Zoology.ENGLISH ABSTRACT: The adaptibility of the halophytic plant Triglochin bulbosa to pollution of the Berg River estuary and high concentrations of sodium chloride was investigated. The relation of plant to environment was determined by means of comparative analysis of plant and substrate, an anatomical study and cultivation of plants in culture solutions of various concentrations and osmotic potentials. Knowledge of the mechanism of ion absorption was obtained by short-term studies of the absorption of cations by excised roots.
- ItemAssembly and disassembly of bird pollination communities at the Cape of Africa(Stellenbosch : Stellenbosch University, 2011-03) Geerts, Sjirk; Pauw, A.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: With the current global decline in pollinators, and the concurrent decline in plant species, pollination research is becoming increasingly important. However, studies outside Europe and North-America and on groups other than insects are needed to make generalisations possible. In this thesis I study how pollination structures plant and bird communities in a biodiversity hotspot, the Cape Floristic Region of South Africa. I show that bird-plant pollination mutualisms are an important ecological factor structuring ornithophilous Proteaceae and nectar-feeding bird communities. This close association between plant and bird communities suggests an important role for community wide pollination mutualisms. How these mutualisms disassemble in reaction to a range of anthropogenic impacts is determined. Firstly, I use experimental manipulation of honeybee density to test whether honeybee farming affects nectar-feeding birds. Hive addition increased honeybee abundance far above natural levels but nectar-feeding bird pollinators were not consistently affected. Secondly, I document the impact of a two lane tar road on the bird pollination community. The two-fold decline found in pollination along roadsides, should have important implications for the way we view and manage road verges for ecological processes. Thirdly, I investigated how fragmentation affects bird-pollination communities by assessing an endangered, bird-pollinated plant, Brunsvigia litoralis. The only flower visitor at the urban sites, the shorter billed Greater Double-collared Sunbird is unable to access the nectar due to a long perianth tube. The longer billed Malachite Sunbird was the sole pollinator of B. litoralis at the rural site, significantly increased seed set. The lack of ecological analogs in these urban fragments might place pollinator specialist plants, such as B. litoralis, at risk. Fourthly, fire is a frequent disturbance in communities of bird-pollinated plants. In a before/after fire observation study and a burnt/unburnt transplant study, birds visited flowers in the “before fire” and “unburnt” areas only. The results are surprising given the large number of bird-pollinated plants flowering in the early post-fire vegetation. Lastly, I find that alien invasive plant species are incorporated into the native pollination community in a spectacular way; sunbirds adapt to a hummingbird-like, hovering lifestyle to obtain nectar. Alien invasive plants greatly increase nectar-feeding bird abundance; in turn, birds enhance seed set in these alien plants. I conclude by asking whether the disassembling of bird pollination communities really matters. To answer this question I report on a decade of demographic data on the geophytic bird-pollinated Brunsvigia orientalis. In the demographic analysis, the elasticity component for reproduction was more important than expected for a long lived plant. Reduced population growth in the shade and a large investment in a winged inflorescence, suggest B. orientalis is a light demanding, well dispersed, gap colonising species. The link between pollination and seed has been made before, but I take this one step further and show that pollination intensity predicts population growth rate. By linking plant demography and pollination, I was able to predict the future of plant populations under variable pollination conditions. The disassembly of bird pollination communities only becomes important for population persistence once the mutualism has almost entirely broken down.
- ItemAssessing the evolutionary and physiological resilience of southern African marine species(Stellenbosch : Stellenbosch University, 2021-04) Mertens, Lisa; Measey, John; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Assessing the genomic basis of local adaptation and critical thermal limits is essential for anticipating species persistence and distribution under climate change. Environmental gradients are associated with genomic and physiological differences between populations. South Africa's two ocean regime creates a thermal gradient, which delimits distinct bioregions between its cold-temperate west coast, warm-temperate south coast and warmsubtropical east coast. Three co-distributed key rocky shore invertebrate species representing different phyla were selected for a multi-species approach. The objectives of this dissertation were to 1) identify selectively neutral genomic loci and neutral population structure, 2) determine putatively adaptive loci and adaptive population structure, 3) explore functional annotations and 4) measure critical thermal limits (CTmin, CTmax). Pooled RAD-Seq (ezRAD) was utilised to identify selectively neutral shared and populationspecific single nucleotide polymorphisms (SNPs) in six populations of shore crab Cyclograpsus punctatus (CP), granular limpet Scutellastra granularis (SG), and Cape sea urchin Parechinus angulosus (PA). Population-specific SNPs were detected in all populations. Nucleotide diversity indices (Tajima.s pi, Watterson.s theta)) appear heightened in PA's northern west coast population compared to the remaining sites. Estimated pairwise FST values range from 0.043-0.055 (CP), 0.044-0.066 (SG) to 0.039-0.089 (PA). Selectively neutral genomic population structure indicates instances of intraspecific subdivisions present in all populations. All species populations harbour unique SNPs, yet increased nucleotide diversity is only detected in PA. The empirical FST-method, BayeScan and BayeScEnv identified overall 1102 outliers under positive selection, of which 69 (CP), 11 (SG) and 27 (PA) could be functionally annotated. Candidate loci are involved in various cellular functions including membrane transport, vesicle signalling, protein folding/modification and cytoskeleton function. Identified loci related to energy cycling might point to selection on metabolic capacity to counter environmental stressors. Environmental differentiation of sea surface temperature (SST), salinity and air temperature could be associated with several putative outliers. There is no isolation-by-distance (IBD), but isolation-by-environment (IBE) suggests salinity variation to account for 48% of genomic variation in P. angulosus and SST and air temperature for 45% in S. granularis. Outlier-based population structure indicates possible intraspecific subdivision in some species. Critical thermal limits (CTmin, CTmax) were investigated with thermal tolerance trials and compared to local min/max environmental temperature for warming and cooling tolerance. Across populations, mean CTmin ranges from -1.5-0.6°C (CP), -0.4-3.2°C (SG) to 5-10.9°C (PA). Mean CTmax ranges from 43.8-46.1°C (CP), 34.4-35.7°C (SG) to 28.9-32.4°C (PA). West coast crabs have significantly higher CTmax than east coast crabs. CTmin is negatively and thermal breadth positively correlated with body mass (CP, PA). Significant regional differences in mass were detected (SG, PA). Warming and cooling tolerance appears sufficient, requiring further investigation within situ microhabitat data. East coast rocky shore populations likely face future warm-edge range contractions, whereas the south coast might experience distributional shifts depending on local thermal conditions. The west coast is an anchor for rocky shore species in South Africa and represents a possible climate change refugium. Strategic recognition in regional marine conservation management is warranted.