Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The primary aim of this study was to assess and compare the ecological integrity of the Lourens, Palmiet and Hout Bay Rivers (South Western Cape, South Africa) by examining the macroinvertebrate community structure at a series of representative sampling sites along the course of each river, using the South African Scoring System - Version 5 (SASS-5) rapid bioassessment method. Secondary aims included an examination of the effects of seasonal variability, biotope availability and site-specific environmental variables on the macroinvertebrate community structure at sampling sites, as well as the preliminary testing of the Integrated Habitat Assessment System (IHAS) for aquatic macroinvertebrates. According to results obtained, the ecological integrity of sampling sites in the Mountain Stream Zone of the three rivers was consistently good. The Hout Bay River in the upper portions of the Orange Kloof Reserve was particularly near-pristine, with this area having been identified in this study as a potential biodiversity ‘hot-spot’ for aquatic macroinvertebrates. Downstream of the Mountain Stream Zone, there was a significant deterioration in the ecological integrity of all three rivers due to a number of probable causes. Results based on recorded SASS Scores and Average Score per Taxon (ASPT) values, using ‘biological bands’ generated from reference sites in the South Western Cape, were generally similar to and supported by the corresponding multivariate analyses undertaken. From the results of the various analyses undertaken in this investigation and some of the problems encountered in interpreting the data, a number of recommendations are made regarding future bioassessment studies based on the SASS within the national River Health Programme (RHP). To test the IHAS, secondary data were obtained from reference sites in the Mpumalanga and Western Cape Provinces of South Africa. Assuming that SASS Scores at reference sites are the highest scores attainable, one would expect to find a positive relationship between SASS Scores and IHAS scores at reference sites. The assumption in this investigation was that this relationship should be linear. Non-parametric correlation analyses were undertaken between SASS-4/5 Scores and IHAS scores, using Kendall’s Rank-correlation Coefficient (τ), with separate analyses undertaken for different geomorphological zones and biotope groups. Correlations between SASS Scores and IHAS scores were generally weak (τ-values mostly < 0.3) and unsatisfactory, with no significant correlations (p < 0.05) for two-thirds of the data sets analysed and a wide degree of scatter generally observed amongst data points in respective scatter plots. The performance of the IHAS varied between geomorphological zones and biotope groups, with the Foothill: Gravel-bed Zone in Mpumalanga showing the best results, particularly when the stones-in-current biotope group was analysed separately. Further testing of the IHAS is required to confirm its relative performance in different bioregions/ecoregions, geomorphological zones and biotope groups, which should be undertaken as a priority research area within the RHP. Unsuccessful attempts to test the IHAS by means of multiple regression analyses were undertaken, suggesting that such techniques should be avoided in further testing of the IHAS. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie studie was om die ekologiese toestand van die Lourens-, Palmiet- en Houtbaairiviere (Suidwes Kaap, Suid Afrika) te bepaal en te vergelyk deur die bestudering van die makroinvertebraatgemeenskapstruktuur by verteenwoordigende monsterpunte langs die riviere, met gebruik van die “South African Scoring System” – Weergawe 5 (SASS-5) snelle biologiese bepalingsmetode. Sekondêre doelwitte het die bepaling van die gevolge van seisoenele veranderlikheid, biotoop beskikbaarheid en ligging-bepaalde omgewingsveranderlikes op die makroinvertebraatgemeenskapstruktuur by monsterpunte ingesluit, asook die inleidende toetsing van die “Integrated Habitat Assessment System” (IHAS) vir watermakroinvertebrate. Volgens die resultate verkry, was die ekologiese toestand van monsterpunte in die Bergstroomsone van die drie riviere konsekwent goed. Die Houtbaairivier in die boonste gedeelte van die Oranjekloofreservaat was veral feitlik onversteurd en hierdie streek is in die studie as ‘n potensiaal biodiversiteit “hot-spot” vir watermakroinvertebrate geidentifiseer. Stroomafwaarts van die Bergstroomsone was daar ‘n beduidende verswakking in die ekologiese toestand van al drie riviere, as gevolg van ‘n aantal moontlike oorsake. Resultate gebaseer op bepaalde “SASS Scores” en ‘Gemiddelde Waarde per Takson’ (“Average Score per Taxon” - ASPT) waardes, met gebruik van ‘biologiese bande’ wat van verwysingsmonsterpunte in die Suidwes Kaap afgelei is, was oor die algemeen soortgelyk aan en gestaaf deur die ooreenstemmende multiveranderlikke (“multivariate”) statistiese analises wat gedoen is. Uit die resultate van die verskeie analises wat in hierdie ondersoek gedoen is en sommige van die probleme wat in die dataverklaring gevind is, is ‘n aantal aanbevelings gemaak met betrekking tot toekomende biologiese bepalingstudies vir die nasionale Riviergesondheidsprogram (“River Health Programme” - RHP) wat op die SASS gebaseer is. Om die IHAS te toets is sekondêre data van verwysingsmonsterpunte in die Mpumalanga en Wes Kaap Provinsies van Suid Afrika verkry. As aangeneem word dat die “SASS Scores” by verwysingsmonsterpunte die hoogste moontlike tellings is wat bereik kan word, sou ‘n positiewe verwantskap tussen “SASS Scores” en IHAS tellings by verwysingsmonsterpunte verwag word. Die veronderstelling in hierdie studie was dat dié verwantskap lineêr moet wees. Nie-parametriese korrelasieanalise tussen “SASS-4/5 Scores” en IHAS tellings is gemaak, deur gebruik van Kendall se Rangkorrelasiekoëffisiënt (τ), met afsonderlike analises vir verskillende geomorfologiese sones en biotoopgroepe verrig. Korrelasies tussen “SASS Scores” en IHAS tellings was algemeen swak (τ-waardes < 0.3) en onbevredigend, met geen beduidende korrelasies (“p” < 0.05) vir twee-derdes van die datastelle wat geanaliseer is nie en ‘n wye verspreiding tussen datapunte in die onderskeie “scatter plots” wat waargeneem is. Die funksionering van die IHAS was verskillend tussen geomorfologiese sones en biotoopgroepe. Die beste resultate is vir die Voorheuwel: Gruisbeddingsone in Mpumalanga verkry, veral indien die klippe-in-stroom biotoopgroep afsonderlik geanaliseer is. Verdere toetsing van die IHAS is nodig om die relatiewe funksionering in verskillende biostreke/”ecoregions”, geomorfologiese sones en biotoopgroepe te bevestig en dit behoort voorangs te geniet binne die RHP. Pogings om die IHAS deur middel van veelvoudige regressie analise te toets het misluk, wat aandui dat sulke tegnieke vermy moet word in verder toetsing van die IHAS.

Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT:This study concentrates on the Bontebok (Damaliscus pygargus pygargus Pallas 1766) population of the Bontebok National Park. Using a combination of literature research, field observations, satellite imagery, Geographic Information System mapping and dung analysis, their habitat preferences within the Park are ascertained and compared to different behavioural and environmental factors. Considering vegetation composition and height, grass cover, burning history, general topography, water availability, actual diet quality (from faecal analysis) and population distribution, the best predictor of spatial pattern are investigated with GIS Dempster-Shafer models. The historical density distribution of the animals in the Park can be used to predict sustainable stocking rates. As far as possible, the results for the Bontebok are compared to those of the other larger herbivores in Bontebok National Park i.e. Red Hartebeest, Cape Mountain Zebra and Grey Rhebuck. These results should be useful for Wildlife Managers to know how to manage veld for Bontebok and at what stocking rates this can be done sustainably. / AFRIKAANSE OPSOMMING: Hierdie studie fokus op die Bontebok (Damaliscus pygargus pygargus, Pallas 1766) bevolking van die Bontebok Nasionale Park. Deur ‘n kombinasie van literatuurstudie, veldobservasies, satlietbeelde, Geografiese Inligtingstelsel (GIS) kartering en mis-analise te gebruik, word Bontebok habitatvoorkeure in die Park vasgestel en met verskillende gedrags- en omgewingsfaktore vergelyk. Deur te kyk na plantegroei-samestelling en hoogte, grasbedekking, brandgeskiedenis, algemene topografie, water-beskikbaarheid, diëet kwaliteit en die Bontebokke se waargenome ruimtelike verspreiding, word die faktor wat die verspreidingspatroon die beste voorspel, m.b.v. GIS Dempster-Shafer modelle ondersoek. Die historiese digtheidsverspreiding van diere in die Park word gebruik om volhoubare veldladings te voorspel. Sover moontlik word die resultate vir Bontebok vergelyk.met die ander groter herbivore in die Bontebok Nasionale Park, te wete Rooi Hartebees, Kaapse Bergsebra en Vaalribbok. Hierdie resultate behoort vir Natuurlewe-bestuurders tot nut te wees as riglyne vir veldbestuur en volhoubare veldladings van Bontebok.

Thesis (MSc)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: Understanding the responses of species to climate change is a scientific problem that requires urgent attention, especially under current conditions of global climate change. The large and rapid rates of climate change reported for sub-Antarctic Marion Island makes the island highly suitable for studying the biotic consequences of climate change. Furthermore, the extreme environments on the island result in a close coupling of the biotic (e.g. population dynamics) and abiotic (e.g. climate) factors. Therefore, examining the response of the dominant and keystone plant species on the island, Azorella selago Hook. (Apiaceae), to climate-associated environmental change (e.g. temperature) may provide insight into how A. selago and the associated species communities will be affected by climate change. This study described the variability in microclimate temperatures associated with A. selago across altitudinal gradient and between the eastern and western sides of Marion Island. Microclimate temperatures were also compared to the island’s Meteorological data to determine variation between temperatures experienced by A. selago cushion-plants in the field and those recorded at the island’s Meteorological Station. Temperature variation inside and outside A. selago cushions was also examined. Azorella selago cushions were found to have a buffering effect on temperature, such that species occurring epiphytically on A. selago experience more moderate temperatures than the surrounding environment. However, A. selago were found to experience more extreme temperatures than temperatures recorded at the Meteorological Station. Therefore, A. selago may possibly experience greater environmental warming than recorded by the Meteorological Station. While temperatures decline with altitude, temperature conditions on the western side of the island were more temperate than the eastern side. This presents the first record of temperature conditions on the western side of the island. This study also quantified fine-scale (e.g. within-site) and broad-scale (e.g. island-wide) variability patterns of A. selago (morphology, phenology, and epiphyte load) across Marion Island. Altitudinal gradient and climatic exposure at different sides of the island were used to understand the likely effects of climate associated environmental change on this dominant component of the fellfield habitat. Site-specific processes were found to determine the spatial structure of A. selago characteristics at fine-scales. However, broad-scale observations established strong responses of A. selago characteristics to altitudinal gradients and different sides of the island. Azorella selago morphological features (e.g. plant size and leaf size) were found to be more responsive to differences between the eastern and western sides of the island than to altitudinal gradient. Azorella selago micro-morphological features (e.g. leaf trichomes and stomatal densities) were also found to be more responsive to climatic exposure at different sides of the island than to altitudinal gradient. However, differences in A. selago epiphyte density (e.g. Agrostis magellanica) and phenology resembled microclimate temperatures in that they were more responsive to altitudinal gradient than to side of the island differences. From these results it can therefore be predicted that the A. selago of Marion Island is likely to be morphologically fairly resilient to moderate climatic shifts, although at lower altitudes and on the eastern side of the island, it may be outcompeted by the epiphytic grass, Agrostis magellanica. The results also suggest that the warming climate of Marion Island may result in an early occurrence of phenological processes particularly at lower altitudes and the eastern side. Azorella selago at lower altitudes and on the eastern side of Marion Island are therefore expected to largely show more symptoms of climate change (e.g. warming) on this species. Azorella selago is also predicted to move up altitudinal gradients in response to warming. / AFRIKAANSE OPSOMMING: ’n Begrip van hoe spesies reageer op klimaatsverandering is ’n wetenskaplike vraag wat onmiddellike aandag benodig, veral onder huidige globale klimaatsverandering. Die groot en snelle tempo waarteen klimaatsverandering waargeneem word op sub-Antarktiese Marion Eiland, maak die eiland hoogs geskik om die biotiese gevolge van klimaatsverandering te bestudeer. Verder veroorsaak die uiterste omgewing van die eiland tot ’n nabye koppeling tussen die biotiese (bv. populasie dinamika) en abiotiese (bv. klimaat) faktore. Dus, deur die reaksies van ’n dominante- en sleutel-spesie op die eiland, Azorella selago Hook. (Apiaceae), op klimaat-geassosieerde omgewings verandering (bv. temperatuur) te bestudeer, mag insig verskaf hoe A. selago en geassosieerde spesie gemeenskappe geaffekteer sal word deur klimaatsverandering. Hierdie studie beskryf die wispelturigheid in mikroklimaat temperature geassosieer met A. selago oor ’n hoogte gradiënt asook tussen die oostelike en westelik dele van Marion Eiland. Mikroklimaat temperature was ook vergelyk met die eiland se Meteorologiese data met die doel om die mate van variasie tussen temperature verduur deur A. selago kussing-plante in die natuurlike omgewing met die van die eiland se Meteorologiese stasie te vergelyk. Temperatuur variasie binne en buite A. selago kussing-plante is ook vasgestel. Dit was gevind dat Azorella selago kussing-plante die temperatuur buffer, met die gevolg dat spesies wat epifities op A. selago voorkom, meer gematigde temperature ondervind as die onmiddellike omgewing om die plant. Daar is egter gevind dat A. selago meer uiterste temperature ondervind as temperature gemeet by die Meteorologiese stasie. Dus mag A. selago groter omgewings verwarming ervaar as wat temperature gemeet by die Meteorologiese stasie dui. Terwyl temperatuur afneem met ’n toename in hoogte, was temperatuur aan die westekant van die eiland mere gematig as die oostekant. Dit verskaf die eerste rekord van temperatuur toestande aan die westekant van die eiland. Hierdie studie bepaal ook die fyn-skaal (e.g. binne-terrein) en groot-skaal (e.g. oor die eiland) variasie patrone van A. selago (morfologie, fenologie, en epifiet lading) oor Marion Eiland. Die hoogte gradiënt en klimaat blootstelling aan verskillende kante van die eiland is gebruik om die waarskynlike effekte van klimaats-geassosieerde omgewings verandering op die dominante deel van die felfield habitat te verstaan. Daar is gevind dat terrein spesifieke prosesse die ruimtelike struktuur van A. selago se klein-skaal eienskappe bepaal. Groot-skaalse waarnemings dui egter ’n sterk antwoord van A. selago eienskappe op die hoogte gradiënt en aan verskillende kante van die eiland. Azorella selago morfologiese eienskappe (e.g. plant- en blaar grootte) is gevind om meer te reageer op verskille tussen oostelike en westelike kante van die eiland as op die hoogte gradiënt. Azorella selago mikromorfologiese eienskappe (e.g. blaar trigome en stomata digtheid) is ook gevind om meer te reageer op omgewings blootstelling tussen verskillende kante van die eiland as op die hoogte gradiënt. Verskille in A. selago epifiet digtheid (e.g. Agrostis magellanica) en fenologie het egter mikroklimaat temperature gevolg, in dat beide meer gereageer het op die hoogte gradiënt as eiland-kant verskille. Hierdie resultate voorspel dus dat dit waarskynlik is dat A. selago van Marion Eiland morfologies redelik terugspringend sal wees ten opsigte van matige klimaatsverandering, al mag dit uitgekompeteer word deur die epifitiese gras, Agrostis magellanica by lae hoogtes en aan die oostekant van die eiland. Hierdie resultate dui ook dat verwarming van Marion Eiland se klimaat ’n vervroeging van fenologiese prosesse mag hê, veral by lae hoogtes en aan die oostekant van die eiland. Dus word dit verwag dat Azorella selago by lae hoogtes en aan die oostekant van Marion Eiland om meer simptome van klimaatsverandering (e.g. verwarming) te dui. Dit word ook voorspel dat Azorella selago opwaarts teen die hoogte gradiënt sal beweeg in reaksie tot verwarming.

Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2007. / This study assessed (a) the inclusion of local communities in the process of the establishment and management of Parque Nacional do Limpopo (PNL); (b) local community resources use practices, livelihoods strategies, land resources use and ownership and institutional arrangements at the grassroots; and (c) attitudes and perceptions of local communities towards the park and its implications for the sustainability of the park. The study shows that local stakeholders were left out in the planning and implementation processes of the park, which was through top-down approach. There was a lack of involvement of local communities and co-ordination with local stakeholders concerning on-the-ground activities. Local community participation occurs through consultation, thereby depriving primary stakeholders of any decision-making power. However, the study notes that the ongoing interaction between the park management, community advocacy organisations and local communities in the park represents a positive step towards the evolving practice of participatory governance of the protected area. It is also shown that local communities have diverse livelihood strategies, including subsistence agriculture, livestock herding, forest products harvesting, small businesses, handicrafts and cash remittances by migrate labourers. It is worth noting that land and forest resources use constitutes the foundation of their livelihood strategies. Local communities considered land to belong to traditional land chiefs who head local socio-cultural and political organizations in rural areas. They allocate land and control access to natural resources. Other community members asserted that the land belongs to the respective families that inherited and use it. The legal framework in Mozambique authorises the establishment of new institutions at the grassroots. This overlaps with the pre-existing traditional institutions in the rural areas, resulting in power conflicts and in some cases disruption of local institutions for governance ...

Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2005. / The South African table grape industry exports approximately 60% of the table grapes produced. A major threat to the export of these grapes is the phytosanitary risk that insect pests pose. This study was conducted in the Hex River Valley, South Africa’s main table grape producing area. The aim of this study was to reduce the number of phytosanitary rejections from insects on table grapes from the Hex River Valley. Thus the main objectives of the study were to identify the most important phytosanitary pests in the Hex River Valley; the determination of their presence in the vineyards with possible means to control them; and to assess the possibility of using postharvest quarantine treatments in the Western Cape. Further aims were to determine the effect of different colour harvesting crates on the phytosanitary pests and whether the phytosanitary pests infested the grapes via packhouses. The most important phytosanitary pests of table grapes of the Hex River Valley are in order of importance: Phlyctinus callosus (Schonherr) (Coleoptera: Curculionidae), Epichoristodes acerbella Walker (Lepidoptera: Tortricidae), Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), Gonocephalum simplex Fabricius (Coleoptera: Tenebrionidae) and Dysdercus fasciatus Signoret (Hemiptera: Pyrrhocoridae). 12.71% of rejections were from species that were not identified, while a further 33% of the rejections were possibly identified incorrectly. Phytosanitary control of P. callosus appeared to be far more effective using Plantex® than pesticides. Weather conditions appeared to affect the abundance of P. callosus, especially warm weather, while bunches harboured less P. callosus later in the day. Control of E. acerbella with DiPel® (Bacillus thuringiensis var. kurstaki) appeared to at least reduce the population within the vineyards, and so its use is recommended. P. ficus is a non-actionable species for the USA market and is not listed as a phytosanitary pest for the Israeli market and so should not be causing any phytosanitary rejections. C. capitata appeared to be successfully controlled by the fruit fly sterile release program and the cold sterilisation it currently undergoes. G. simplex caused few rejections. It is still unclear where this pest infests the grapes, as it was found in both the field and in the packhouses. D. fasciatus occurrence on grapes was probably accidental. It was shown that picking during the early and late parts of the day, when this species was less active, reduced its occurrence in bunches. Gryllus bimaculatus (De Geer) (Orthoptera: Gryllidae), although not reported as a reason for rejections in table grapes for the past two years, was an actionable species that was present in large numbers in the Hex River Valley. There was a strong correlation between increasing quantities of pesticides and higher abundances of G. bimaculatus. It appeared to be an indicator of the overuse of pesticides. Results of this study showed that infestation by the phytosanitary pests came from neighbouring vineyards. The creation of barriers to prevent the movement of these pests between vineyards is suggested. Methyl bromide is the most commonly used postharvest quarantine treatment. Owing to the ozone-depleting properties of methyl bromide, it is scheduled to be outlawed in many countries from 2005. Alternative postharvest treatments are irradiation, extreme temperatures, forced air, vapour-heat treatments and the use of controlled atmospheres. Irradiation treatments appeared to control the pests at doses that do not damage the grapes. Controlled atmosphere treatments also have a high probability of success, although more research is required on this treatment. Low temperature treatments are relatively cheap as most exported fruit already undergoes cold storage, and appears to control species in the families Pseudococcidae and Tephritidae, although further research is required for the other pest. Colour or location of the harvesting crates in the vineyards appeared not to influence the number of phytosanitary pests collected, as they were not attracted to these crates.

Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The obscure mealybug, Pseudococcus viburni (Signoret) (Pseudococcidae), is one of the common and serious pests of apples and pears in South Africa. The management of this pest in South Africa is dominated by the use of insecticides, while research into using natural enemies for biological control of mealybugs is still ongoing. Increasing concern over the environmental impact, pesticide residues in fruits, resistance, and expense associated with frequent use of insecticides make it necessary to investigate alternative biological control methods, such as the use of entomopathogenic nematodes, for the control of mealybugs. Entomopathogenic nematodes have proven comparable or even superior to chemicals in controlling certain insect pests, without residue problems or a harmful effect on the environment. An important aspect of using endemic nematodes includes the identification of species of nematodes and their symbiotic bacterial cells. A study was carried out to describe a new species of Steinernema, which was recovered during a previous survey in citrus orchards in three provinces of South Africa. Morphometrics, morphology, crossbreeding, drawings, light microscopy and Scanning Electron Microscopy (SEM) photographs were used to describe the new species. A cryopreservation method has been simplified and optimised for the long-term storage of Steinernema khoisanae (SF87) and Heterorhabditis zealandica (J34). Different cryoprotectants used included 15% glycerol, 8% ethylene glycol and 8% dimethyl sulfoxide (DMSO), in which S. khoisanae was incubated at room temperature for periods of two, three, four and five days, followed by a methanol wash. An optimum survival rate of 69% was obtained for S. khoisanae after a four-day incubation period in 15% glycerol. This technique has been used for the cryopreservation of H. zealandica, with a 78% survival rate. The thawed nematodes of both species were able to infect Galleria mellonella larvae after 42 days of cryopreservation (-196ºC) and were able to complete their life cycles. / AFRIKAANSE OPSOMMING: Die ligrooswitluis, Pseudococcus viburni (Signoret) (Pseudococcidae), is een van die algemene en ernstige peste van appels en pere in Suid-Afrika. Die bestuur van hierdie pes word tans in Suid-Afrika deur die gebruik van insekdoders gedomineer terwyl navorsing oor die gebruik van natuurlike vyande vir die beheer van P. viburni nog aan die gang is. Die verhoogde kommer oor die omgewing, residue in vrugte, weerstand, en die koste verbonde aan die gereelde gebruik van chemiese middels maak dit nodig om alternatiewe biologiese metodes van beheer, soos die gebruik van entomopatogeniese nematodes vir die beheer van witluis, te ondersoek. In ander lande is reeds aangetoon dat entomopatogeniese nematodes onder sekere omstandighede en vir sekere insekte gelykwaardige of selfs beter beheer kan gee as chemiese middels. ʼn Belangrike aspek van die gebruik van endemiese nematodes vir die beheer van insekte sluit die korrekte identifikasie van die spesies met hul geassosieerde bakteriese simbionte in. ʼn Nuwe spesie van Steinernema is uit ʼn vorige opname van entomopatogeniese nematodes in sitrusboorde in drie provinsies van Suid-Afrika geïsoleer. Morfometrie, morfologie, kruisteling, ligmikroskoop en SEM fotografie is gebruik om ʼn nuwe spesies te beskryf. ʼn Kriopreserveringsmetode is ontwikkel en ge-optimaliseer vir die langtermyn bewaring van Steinernema khoisanae (SF87) en Heterorhabditis zealandica (J34). Verskillende kriobeskermingsmiddels insluitend 15% gliserol, 8% dimetiel sulfokied (DMSO) en 8% etileen glikol, waarin S. khoisanae vir periodes van twee, drie, vier, en vyf dae geïnkubeer is, is teen kamertemperatuur, getoets, gevolg deur ʼn metanolbad. Optimum oorlewing van 69% is verkry vir S. khoisanae nadat die infektiewe larwes (IJ) vir vier dae in 15% gliserol gehou is. Hierdie tegniek is ook toegepas op H. zealandica, met 78% oorlewing van die IJ. Die ontvriesde nematodes van beide spesies was in staat om Galleria mellonella larwes suksesvol te infekteer en hulle lewensiklus te voltooi nadat hulle vir 45 dae onder kriopreservering gehou is teen -196ºC.

Thesis (MScConsEcol(Conservation Ecology and Entomology)--University of Stellenbosch, 2007. / Riparian areas are highly complex systems with varying levels of disturbance that are highly susceptible to invasion by alien plants. Once invaded, riparian areas play a major role in the dispersal and spread of invasive alien plants (IAPs) through the river system and, in some cases, to neighbouring landscapes. Riparian areas have therefore been prioritized by many alien clearing initiatives in South Africa. Current practice for the restoration of cleared areas is minimal and relies mainly on the un-aided recovery of native species from residual individuals and soil stored seed banks. Little research, however, has been done on the effectiveness of this approach or the extent to which riparian seed banks contribute towards community restoration. This study is part of a national research initiative (Targets for Ecosystem Repair in Riparian Ecosystems in Fynbos, Grassland and Savanna Biomes) funded by Department of Water Affairs and Forestry, in collaboration with Working for Water, The Centre for Invasion Biology and the Universities of Cape Town, Stellenbosch, Rhodes and Witwatersrand. The initiative undertook to investigate different restoration techniques on various invaded sites for their cost-effectiveness, efficiency, practicality and conservation integrity. This study has three aims. The first is to determine the composition of seed banks in un-invaded riparian areas within the fynbos biome to be used as a benchmark for future research, restoration grading and other management requirements. The second aim is to determine the composition of seed banks in heavily invaded riparian areas, and thus to assess the impact of invasion on the integrity of the seed banks. The third aim is to evaluate the restoration potential of riparian seed banks following the clearing of invasive alien plants (IAPs). Study sites were selected within four river systems in the south-western part of the Western Cape Province in South Africa: the Berg, Eerste, Molenaars and Wit Rivers. Plots were selected in both invaded (>75% IAP canopy cover; considered “closed” alien stands) and un-invaded (also termed reference, with <25% IAP canopy cover) sections of the river. Replicate plots were established along varying gradients of elevation (mountain stream and foothill) and moisture regimes (dry, wet and transitional bank zones). Soil samples were collected together with above-ground vegetation surveys and comparisons were made. Results from this study confirm those of previous studies that seed banks offer little reference to current aboveground vegetation, but rather offer insight into past vegetation history as well as future vegetation assemblages. Worldwide, many of the species that characteristically form seed banks are early successional species. A community study was done for the seed bank based on the species that germinated and were identifiable at termination of the project (6 months after initiation). Three clusters of species could be identified. One group comprised 32 generalist species that occurred in both reference and invaded sections of the rivers. A second group comprised 39 species associated with invaded sites, and a third group of 40 species that was associated with reference sites. A few sub-community groups were found within both the “reference” and “invaded” community groups which were assumed to be habitat specific. Most species were “pioneer” or relatively-short lived, early-successional species which play a vital role in the initial post-disturbance vegetation cover, and facilitate establishment of later successional species. Seed banks are notoriously variable over space and time, and floristic representation is often biased as a result of differences among species in seed production, dispersal and longevity in the soil. The general consensus is that seeds have an irregular, clustered spatial distribution that is dictated by both biological and environmental factors. Within river systems, the irregular clustering can be exceptionally skewed with the influence of pockets of high sediment deposition along the bank. Environmental factors that were found to significantly skew germination results were the presence of fire, as well as the extent and intensity of invasion (duration and cover). The high level of diversity and abundance in reference Berg River mountain stream seed banks was perceived to be a direct result of a moderate fire frequency (between 8-15 years) and the relatively natural state of the vegetation (i.e. very little invasion). Also, diversity and richness of indigenous species from the Wit and Molenaars Rivers were substantially higher in the invaded samples than the reference samples, probably because both river systems have a long history of invasion and other anthropogenic disturbances which would have an effect on the samples from “reference” sections (i.e. even a 25% presence of IAPs seems adequate enough to alter the composition of the seed bank). Correspondence analyses showed that species had clear affinities towards different levels of “key” riparian environmental variables (fire, invasion and anthropogenic disturbance). Most species were associated with moderate levels of fire frequency, invasion history, and anthropogenic disturbance. Comparisons of seed bank species assemblages between the lateral and longitudinal variables of the rivers offered insights into the habitat requirements of certain fynbos and riparian species. Most significant were the results from bank zone comparisons which showed distinct species groupings along the different moisture bands. As could be expected, riparian species were best represented within the wet bank zones and fynbos species within the dry bank zone, while species characteristic of both zones occurred in the transitional zone, making this seed bank zone the richest in species. Mountain stream sections were richer and more diverse than foothill sections over both invaded and reference samples. This is hypothesised to be linked to lower levels of anthropogenic disturbance experienced in the mountain stream sections. The impact of invasion on the riparian seed bank was most clearly shown through the correspondence analyses for the 20 most frequently occurring species. The seed bank assembly patterns were clearly defined by the state of the river (reference or invaded). Interestingly, this pattern was evident at all three spatial scales; landscape (rivers), reach (mountain stream and foothill sections) and habitat (dry, wet and transitional zones). The reference seed bank assemblage was more tightly grouped, implying that the species were more closely associated with each other and less variable than those of the invaded seed bank assemblages. The species groupings within the invaded seed banks were influenced by variables such as reach and zone, whereas the reference seed bank assemblages seem relatively unaffected by these variables. This implies that the presence of invasive alien plants creates additional variation within the seed bank which alters the natural groupings. At a broad scale, the invaded seed banks were less species rich. This means that not only will the resulting seedling community be harder to predict, but it will also have fewer species. However although generally lower in species richness, the seed banks from almost all invaded rivers interestingly showed a higher diversity of indigenous species than their reference counterparts. This is very promising in terms of rehabilitation of post-cleared riparian sites, but more information is needed to understand the seed bank composition and determine how sustainable the seed banks are for rehabilitation in the long-term. All invaded sections had fewer herbaceous perennial species but more herbaceous annual species. Graminoids made up 50% or more of the seed bank regardless of state (reference or invaded), while woody species (shrubs/shrublets) were generally more prevalent in the reference samples. These results imply that following the removal of invasive alien plants, the vegetation to regenerate from the seed bank is likely to comprise of short-lived, herbaceous species that are not necessarily an accurate reflection of the indigenous riparian community. It is however important to note that this study investigated only the species that were able to germinate over the study period (6 month germination period). Many riparian species may not have been represented because they are either late germinators or may not be present in the soil seed bank at all. In order to gain a holistic understanding of riparian community recruitment, it is recommended that seed bank studies such as this one be included in a more broad scale, long term investigation which takes into account various reproductive strategies used by riparian species. Research of this nature is in its infancy worldwide and there are many challenges involved in measuring diversity and change in these systems. However, within the scope of this study, I suggest that these results shed light on previously unanswered and important questions regarding the ecology of seed banks in the riparian ecosystems of the Western Cape.

Thesis (MScAgric (Conservation Ecology and Entomology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The banded fruit weevil, Phlyctinus callosus (Schönherr), is a key pest of apples, nectarines and grapevines in the southern areas of the Western Cape. The control of P. callosus is not satisfactory and the insecticides used to control this insect have not proved to be effective since the development of tolerance to pyrethroids and acephate. A control method that can be used, despite it being very labour-intensive, is that of tree trunk barriers. The use of such a method will prevent the weevils from reaching the fruit, as they are unable to fly. Alternative control options, such as the use of entomopathogenic nematodes, are urgently needed for the control of P. callosus. Entomopathogenic nematodes belonging to the Steinernematidae and Heterorhabditidae are ideal biocontrol agents for incorporation into an integrated pest management programme. In order to develop control strategies for P. callosus, large numbers and a predictable quantity of different weevil stages are needed. Especially large numbers of larvae are needed, as this is the stage that will be targeted with nematodes. One of the aims of the current study was to assess various artificial diets for rearing larvae of P. callosus. Though adult weevils were easily collected from orchards, it was very difficult to obtain large numbers of larvae. Modified versions of an agar diet, as well as different carrot based diets, were tested at 21°C. The highest percentage survival obtained for the agar diet was 50% and 60% for one type of carrot diet. A better rearing method proved to be that of planting full-grown carrots in pots, kept at 25°C, resulting in the attainment of the highest percentage survival rate of 90%. A study was undertaken to assess how long, and at what temperature, P. callosus eggs could be stored. A mean percentage hatch of 45.7% was obtained when eggs were stored at 4°C for 70 days. Eggs started hatching after 47 days and 10 days, when stored at temperatures of 11°C and 14°C, respectively. If the aim of the employment of such a method is only to delay egg hatching, the two temperatures (11°C and 14°C) will be suitable. For the following part of the study, several entomopathogenic nematode isolates were evaluated for their potential use as biological control agents against P. callosus. The susceptibility of P. callosus larvae and adults to nematode infection was assessed in the laboratory by screening for their mortality, using different nematode isolates. Larvae were found to be more susceptible to nematode infection than adults. Heterorhabditis isolates were found to cause higher levels of mortality than the Steinernema isolates during screening, when a concentration of 400 infective juveniles (IJ) per insect V was used. Biological characteristics, such as the effect of different temperatures on nematode activity and the minimum concentration of nematodes needed to obtain acceptable levels of control for P. callosus, were also investigated. The percentage mortality ranged from no infection to 75% after four days for the larvae, and the SF41 isolate of Heterohabditis zealandica was selected as the most promising isolate for further laboratory experiments. The vertical movement of nematodes in sand, compared with such movement in sandy loam soil, and the biology of H. zealandica in P. callosus larvae was also investigated in laboratory bioassays. After four days, the LD50 and LD90 values were 96 IJ/50 μl and 278 IJ/50 μl, respectively. Nematodes were found to be inactive at 11°C, with the highest mortality rate of P. callosus resulting from nematode infection being recorded at 25°C. A higher percentage mortality rate was obtained with the sandy loam soil (95.2%) than with the sand (77.5%). Heterorhabditis zealandica could successfully complete its life cycle in 6th instar P. callosus larvae. The study showed that P. callosus larvae are suitable hosts for H. zealandica, and that the control of P. callosus in the field by the selected isolate holds promise. The persistence of the SF41 isolate of H. zealandica at different concentrations was investigated in the last part of the study. The experiment took place in a blueberry orchard, subject to a high rate of infestation by P. callosus. Concentrations of 0, 20, 30 and 45 IJ/cm2 were topically applied, with persistence being evaluated for days 1, 35 and 84. Percentage persistence for 30 IJ/cm2 was calculated as 87.5% for days 35 and 84. The persistence of soil samples taken on day one, and kept in plastic containers at room temperature, was again evaluated on day 128, with the finding that both 30 IJ/cm2 and 45 IJ/cm2 caused 100% mortality of Tenebrio molitor (L.). Results indicated good persistence of H. zealandica after 84 days in field conditions, with a high maintenance of P. callosus populations. The study indicated the potential use of H. zealandica for the control of P. callosus, with the possibility of persistence for at least three months. Future research into the control of P. callosus with nematodes should aim to investigate the technical aspects of field application. The current study shows that entomopathogenic nematodes have potential for controlling the soil stages of P. callosus. The capacity to rear large numbers of P. callosus larvae in the laboratory, for later use in laboratory and field trials, is of key importance. / AFRIKAANSE OPSOMMING: Die gebande vrugtekalander, Phlyctinus callosus (Schönherr), is ʼn groot plaag in appel- en nektarienboorde sowel as wingerde in die suidelike gebiede van die Wes-Kaap. Phlyctinus callosus word nie voldoende beheer nie, en plaagdoders wat voorheen gebruik is om dié insek in toom te hou, het doeltreffendheid ingeboet weens weerstandontwikkeling teen piretroϊede en asefaat. ʼn Alternatiewe beheermetode is stamsperbande. Omdat die kalanders nie kan vlieg nie, moet hulle teen stamme uitklim om die vrugte te bereik. Stamsperbande versper dus die insekte se toegang tot die vrugte, maar is baie arbeidsintensief. Meer haalbare metodes vir die beheer van P. callosus is daarom dringend nodig, en die gebruik van entomopatogeniese nematodes blyk ʼn besliste moontlikheid te wees. Entomopatogeniese nematodes, wat tot die Steinernematidae en Heterorhabditidae behoort, is uitstekende biobeheermiddels vir insluiting by geϊntegreerde plaagbeheerprogramme. Om doeltreffende beheerstrategieë vir P. callosus te bedink, is groot en voorspelbare hoeveelhede kalanders nodig veral groot hoeveelhede larwes, aangesien nematodes op hierdie ontwikkelingstadium gemik sal wees. Die eerste doel met die studie was dus om ʼn kunsmatige dieet vir die teling van P. callosus larwes te ontwikkel. Volwasse kalanders kon maklik in vrugteboorde ingesamel word, maar groot hoeveelhede larwes was moeiliker bekombaar. Aangepaste weergawes van ʼn agardieet sowel as verskillende worteldiëte is by 21°C beproef. Die hoogste persentasie larwale groei en -oorlewing op die agardieet was 50%, en 60% op een bepaalde soort worteldieet. Die beste teelmetode blyk egter volgroeide wortels te wees wat in potte geplant is en by 25°C gehou word. Dié metode het ʼn oorlewingspersentasie van 90% opgelewer. ʼn Studie is onderneem om te bepaal hoe lank en by watter temperature P. callosus eiers vir toekomstige gebruik geberg kan word. ʼn Gemiddelde uitbroeipersentasie van 45.7% is verkry toe eiers vir 70 dae by 4°C geberg is. Eiers wat onderskeidelik by 11°C en 14°C geberg is, het ná 47 en 10 dae onderskeidelik begin uitbroei. Indien die doel is om die eiers slegs stadiger te laat uitbroei, sal hierdie twee temperature dus geskik wees. VII Hierna is verskeie entomopatogeniese nematode-isolate vir moontlike gebruik as biologiese beheermiddels vir P. callosus beoordeel. Phlyctinus callosus larwes en volwassenes se vatbaarheid vir nematode infeksie is in die laboratorium bepaal deur dit met behulp van verskillende nematodeisolate vir mortaliteit te toets. Dié toetse het getoon dat larwes meer vatbaar is vir nematode infeksie as volwassenes. In die proefnemings het die Heterorhabditis-isolate hoër mortaliteit as die Steinernema-isolate veroorsaak teen ʼn konsentrasie van 400 infektiewe larwes (IJ) per insek. Biologiese eienskappe, soos die uitwerking van verskillende temperature op nematode aktiwiteit, sowel as die minimum konsentrasie nematodes om aanvaarbare vlakke van beheer uit te oefen, is ondersoek. Die persentasie mortaliteit vir die larwes het ná vier dae tussen 0% en 75% gewissel, en die SF41-isolaat van Heterohabditis zealandica is as die belowendste isolaat vir die res van die proefnemings gekies. Die vertikale beweging van nematodes in sand teenoor leemgrond, sowel as die biologie van H. zealandica in P. callosus larwes, is ook bestudeer. Ná vier dae was die LD50- en LD90-waardes onderskeidelik 96 en 278 IJ/50 μl. Wat temperatuur betref, is daar bevind dat nematodes onaktief is by 15°C, terwyl die hoogste mortaliteit van P. callosus larwes as gevolg van nematode infeksie by 25°C aangeteken is. Die mortaliteit was hoër in die leemgrond (95.2%) as in die sandgrond (77.5%). Heterorhabditis zealandica kon sy lewensiklus suksesvol in 6de instar P. callosus larwes voltooi. Die studie het derhalwe getoon dat P. callosus larwes geskikte gashere is vir H. zealandica, en dat hierdie isolaat dus in die praktyk ʼn doeltreffende beheermiddel vir P. callosus kan wees. Die oorlewing van verskillende konsentrasies H. zealandica is ten slotte bestudeer. Die proefneming is in ʼn bloubessieboord met ʼn groot populasie P. callosus uitgevoer. Konsentrasies van 0, 20, 30 en 45 IJ/cm2 is op die grond (uitwendig) toegedien, en oorlewing is op dag 1, 35 en 84 gemeet. Die persentasie oorlewing vir die 30 IJ/ cm2 konsentrasie was 87.5% op sowel dag 35 as 84. Oorlewing in grondmonsters wat op dag een ingesamel en by kamertemperatuur in plastiekhouers geberg is, is weer op dag 128 beoordeel. Daar is bevind dat sowel die 30 IJ/cm2 as die 45 IJ/cm2 konsentrasie 100% mortaliteit by T. molitor veroorsaak het. Heterorhabditis zealandica blyk ʼn goeie oorlewing te hê ná 84 dae in veld kondisies wat erg met P. callosus besmet is, en is dus ʼn moontlike beheermiddel vir P. callosus, met potensiële oorlewing vir minstens drie maande.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2010. / 134, 43 p. : ill. / ENGLISH ABSTRACT: The Agulhas Plain is a constituent of the Cape Floristic Region, internationally known as a global biodiversity hotspot. The species-rich Agulhas Plain consists mainly of fire-prone fynbos shrublands of which sandstone fynbos covers a significant surface area. This lowland region is characterised by mostly infertile soils yet has unique floristic complexity and contains a high amount of threatened lowland species. Natural vegetation on the Agulhas Plain has been prone to large scale land transformation activities, mainly attributed to the extent of alien plant invasions, urbanisation and agricultural expansion. Fynbos wildflower farming, specifically from natural vegetation, is an important economic activity and contributes to the region‟s agricultural sector. Farmers harvest large quantities of commercial fynbos species and supply these to the market in an attempt to sustain a livelihood. Certain wildflower farming practices (burning, ploughing and broadcast sowing) are applied to natural vegetation in an attempt to increase the abundance of commercial species (i.e. augmentation). Numerous farming practices are used in the industry and the application of these methods can be dynamic and divergent. Furthermore, the implementation of farming practices manifest as anthropogenically induced disturbance events and are a concern for conservation. Previous investigations suggest that farming practices could establish monocultures of commercial wildflower species by reducing species richness and plant diversity of wildflower vegetation. Although the impact of natural disturbance regimes (e.g. fire) and flower harvesting activities have been researched, the impact of farming practices on fynbos structure and composition remains largely unknown. This thesis reports on various aspects related to wildflower farming on the Agulhas Plain. Firstly, by administering a questionnaire, the extent and application of farming practices was investigated. Additionally, the opinion of wildflower farmers (referred to as landholders) about the impact of farming practices on wildflower populations was explored. Secondly, a vegetation survey aimed to assess the impact of farming practices on various structural (regeneration mode and growth form) and compositional attributes (plant family, dominant and rare species) of fynbos. Results from the questionnaire indicate that the application of farming methods are seasonally restricted, often used in varying combinations and relatively small in spatial extent. Furthermore, results show that wildflower farmers have an ecologically acceptable knowledge base and awareness of fynbos management and conservation. Secondly results, obtained from the vegetation survey, imply that natural vegetation subjected to particular farming practices differ from pristine fynbos vegetation by having both altered structural and compositional attributes. However, the impact of farming practices on rare species was less apparent. The conflict between commercial and conservation objectives are apparent from consultation with landholders. Nonetheless, landholders are optimistic about fynbos conservation and conservation can build upon these positive sentiments. Importantly, there is a need to communicate locally with landholders if a sustainable wildflower industry is a priority to stakeholders on the Agulhas Plain. Furthermore, fynbos ecosystems naturally entail complex ecological interactions. Wildflower farming practices reduce the ecological integrity (i.e. altered plant diversity, growth form and plant composition) of wildflower vegetation, at least at the local scale. These farming practices ultimately result both in distorted competitive interactions and disturbance regimes. Therefore, from a conservation perspective, the implementation of these farming practices (ploughing and broadcast sowing) should be cautioned against. / AFRIKAANSE OPSOMMING: Die Agulhas-vlakte vorm deel van die Kaapse Blommeryk; „n gebied wat internasionale bekendheid verwerf het as „n biodiversiteits-brandpunt. Die spesieryke Agulhas-vlakte bestaan hoofsaaklik uit fynbosstruiklande wat geneig is tot veldbrande. Sandsteenfynbos beslaan „n beduidende oppervlak van die gebied (Agulhas-vlakte). Hierdie laagliggende area (Agulhas-vlakte) word meestal deur onvrugbare grondtipes gekenmerk maar beskik nogtans oor unieke fynbos kompleksiteit wat „n aantal bedreigde laagland spesies insluit. Natuurlike plantegroei op die Agulhas-vlakte is onderworpe aan grootskaalse grondgebruik transformasie; hoofsaaklik toe te skryf aan indringer plantegroei, verstedeliking en uitbreiding van landbou. Fynbos veldblomboerdery, spesifiek van natuurlike plantegroei, is „n belangrike ekonomiese aktiwiteit en lewer „n bydrae tot die Agulhas-vlakte se landbou sektor. Boere oes en lewer groot hoeveelhede kommersiële fynbos spesies aan die mark. Sekere veldblom-boerderypraktyke (brand, ploeg en saadstrooi) word ingespan op fynbosveld ten einde die opbrengs en afwisseling van kommersiële spesies te verhoog. „n Verskeidenheid boerderypraktyke word gevolg en die toepassing van hierdie boerderypraktyke is dinamies en uiteenlopend. Voorts manifesteer die implementering van hierdie boerderypraktyke as mensgemaakte versteurings wat kommerwekkend is vanuit „n bewaringsperspektief. Vorige ondersoeke dui moontlik daarop dat boerderypraktyke monokulture van kommersiële veldblomspesies kan vestig deur die veelheid van spesies en diversiteit van veldblomplantegroei te verminder. Ten spyte daarvan dat die impak van natuurlike versteuringsregimes (bv. vuur) en veldblompluk-aktiwiteite reeds nagevors is, bly die impak van veldblomboerderypraktyke op fynbosstruktuur en -samestelling grotendeels onbekend. Hierdie tesis doen verslag oor verskeie aspekte van veldblomboerdery op die Agulhas-vlakte. Eerstens, deur middel van „n vraelys, is die omvang en aanwending van verskillende boerderypraktyke nagevors. Verder is die menings van veldblomboere (na wie verwys word as grondeienaars) ondersoek met die klem op die impak van boerderypraktyke op veldblombevolkings. Tweedens, is „n plantegroei-opname met die doelwit om die impak van landboupraktyke op verskeie strukturele- (regenerasiemodus en groeivorm) en samestellende eienskappe (plantfamilie, dominante- en seldsame spesies) van fynbos vas te stel gedoen. Die resultate van die vraelys dui daarop dat die aanwending van boerderypraktyke seisoenaal beperk word, dikwels in wisselende kombinasies gebruik word en in ruimtelike omvang redelik klein is. Boonop toon die resultate dat veldblomboere oor „n ekologies-aanvaarbare kennisgrondslag en bewustheid van fynbosbestuur en –bewaring beskik. Tweedens, impliseer die resultate, vanuit die plantegroei-opname, dat fynbosveld wat onderwerp word aan sekere boerderypraktyke van natuurlike fynbosplantegroei verskil deurdat dit gewysigde strukturele- sowel as samestellende eienskappe toon. Die impak van die boerderypraktyke op seldsame spesies was egter minder waarneembaar. Die botsing tussen kommersiële- en bewaringsoogmerke blyk duidelik uit konsultasie met grondeienaars. Nietemin is die grondeienaars optimisties oor fynbosbewaring en bewaring kan op hierdie positiewe sentimente staatmaak en voortbou. Dit is belangrik om daarop te let dat dit noodsaaklik is om plaaslik met grondeienaars oorleg te pleeg indien „n volhoubare veldblomindustrie „n prioriteit vir belanghebbendes op die Agulhas-vlakte is. Verder, aangesien fynbos ekosisteme natuurlik komplekse ekologiese wisselwerkings behels, verminder veldblom-boerderypraktyke die ekologiese integriteit (m.a.w. gewysigde plantdiversiteit, groeivorm en plantsamestelling) van fynbosveld, ten minste op kleinskaal (plaaslik). Hierdie landboupraktyke het uiteindelik beide verwronge kompeterende wisselwerkinge asook versteuringsregimes tot gevolg. Vanuit „n bewaringsperspektief moet daar dus teen hierdie boerderypraktyke gewaarsku word.

Thesis (MScConEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Two populations of Acacia mellifera were noted in Pniel, which is a semi-arid savanna, near Kimberley in the Northern Cape province of South Africa. One population appeared on a rocky, andesitic laval ridges (soil pHKCL 6.5-7.0) along the Vaal river. The other appeared in a sandveld area (soil pHKCL 4). Bush encroachment by A. mellifera was found to be more extensive on the rocky areas than in the sandveld and the two habitats differed extensively on soil pH, clay and silt contents and also on water holding capacities. The rocky habitat was thus deduced to have a higher CEC. Seeds were sampled on a logarithmic scale for allozyme analysis and also randomly in each of the two habitats for local adaptation tests, in which case lime (CaCO3) and organic matter (cow-dung) were used in a completely-crossed design. Detected interaction effects (between population source and pH; population source and organic matter and between pH and organic matter) and significant differences could not separate the two populations as the differences occurred across populations. Random genetic differences leading to phenotypic plasticity in the two observed populations, might be responsible for the observed phenotypic differences. Allozymic data showed no significant differences between the two populations and the genetic distance between and within the populations also confirmed that the two populations had not genetically differentiated. The Mantel Test on the two populations, showed nonsignificant results. Nei‟s UPGMA dendrogram revealed that the game farm subpopulations were more primitive and genetically related to each other. Despite differences in allozyme frequencies, between the sampled sites, genetic differentiation was found to be low (FST = 0.337). Nei‟s (1972) original measures of genetic distance ranged between 0.871 and 1.000 with a mean of 0.949 ± 0.053. The study concluded that the two observed populations had not genetically differentiated and no local adaptation could be established rather phenotypic plasticity was evident and resulted in the observed divergent growth forms. Nonetheless, the overall direction of spread of encroachment appeared to be the eastward. / AFRIKAANSE OPSOMMING: Twee bevolkings van Acacia mellifera is gevind in Pniel, wat „n semi-ariede savanna is naby Kimberley in die Noord-Kaap provinsie van Suid-Afrika. Een bevolking het voorgekom op klipperige andesitiese lava riwwe (grond pHKCL 6.5-7.0) al langs die Vaalrivier. Die ander het voorgekom in „n sandveld area (soil pHKCL 4). Bos-oorskryding deur A. mellifera was meer uitgebreid op die klipperige areas as in die sandveld en die twee habitats het noemenswaardig verskil ten opsigte van grond pH, klei en silt inhoud asook waterhoukapasiteit. Dit kan was dus afgelei word dat die klipperige habitat „n hoër CEC het. Die sade was versamel op „n logaritmiese skaal vir allosiem-analise en ook ewekansig in die twee habitats vir lokale aanpassings toetse. In dié gevalle was kalk (CaCO3) en organiese material (koeimis) gebruik in „n totaal-gekruisde ontwerp. Bespeurde interaksie effekte (tussen bevolkings bron en pH; bevolkings bron en organiese material en tussen pH en organiese material) en noemenswaardige verskille kon nie die twee bevolkings skei nie, aangesien die verskille voorgekom het regdeur die twee bevolkings. Ewekansige genetiese verskille wat lei tot fenotipiese plastisiteit tussen die twee waargeneemde bevolkings mag dalk verantwoordelik wees vir die waargeneemde fenotipiese verskille. Allosiem-data het geen beduidende verskille gelewer tussen die twee bevolkings nie en genetiese afstand binne en tussen die bevolkings het ook bevestig dat die twee bevolkings nie geneties gedifferensiëer is nie. Die Mantel toets op die twee bevolkings het geen beduidende resultate gelewer nie. Nei se UPGMA dendogram get gewys dat die wildsplaas bevolkings was meer primitief en geneties verwant aan mekaar. Ten spyte van die allosiem frekwensies tussen die gemonsterde gebiede, was die genetiese differensiasie laag (FST = 0.337). Nei (1972) se oorspronlike meeting van genetiese afstand het tussen 0.871 en 1.000 beloop met „n gemiddeld van 0.949 ± 0.053. Die studie het bepaal dat die twee waargeneemde bevolkings nie geneties gedifferensiëer het nie en dat geen lokale aanpassing teenwoordig was nie. Fenotipiese plastisiteit was duidelik waarneembaar en het gelei tot die divergerende groeivorme. Nieteenstaande, was die algehele rigting van oorskryding ooswaarts.