Thesis (MScConsEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2006. / Acacia karroo is widespread in southern Africa and displays remarkable phenotypic plasticity over its geographical range. However, it is currently unknown whether this phenomenon is merely phenotypic variation due to environmental variance or whether such plasticity represents adaptation to different habitats (known as adaptive phenotypic plasticity). Adaptive phenotypic plasticity implies that genotypes differ and that there is local adaptation to the local environment. To shed light on this phenomenon, we used a common-garden experiment to investigate among-population variation in plastic responses to simulated rainfall and browsing in two populations originating from contrasting environments, namely arid Karoo (Leeu Gamka) and subtropical coastal forest (Richards Bay). We also studied genetic variation among populations by means of allozyme markers. The results suggest that the populations investigated are both genetically distinct and phenotypically plastic. In addition, there were high levels of polymorphism within populations and great differences in their range of plastic responses to treatments. Of the two populations investigated, the slow-growing one (Leeu Gamka) was phenotypically more plastic with regard to defence-related traits (longer spines, more tannin) while the fast-growing one (Richards Bay) was phenotypically more plastic regarding growth-related traits (taller, with longer leaves). Patterns of performance revealed that the populations have pure strategies of either growth (forest) or defence (arid). The interactions between populations and environments in some traits indicated genetic differentiation in plastic responses between populations and, consequently, that phenotypic plasticity is locally adaptive and not merely due to environmental differences. The two populations appear to have pure strategies; when environmental conditions were improved by addition of water, the forest population increased investment in growth but not defence, while the arid populations increased defence production but not growth.

Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Planococcus citri (Risso) (Hemiptera: Pseudococcidae), the citrus mealybug, is a highly destructive pest of citrus in South Africa. The ability of mealybugs to develop resistance to chemicals, as well as their cryptic nature and protective wax coverings, all individually and combined, impair the ability of insecticides to control them. Furthermore, chemicals deplete natural enemy populations that usually establish control over mealybug populations well before harvest in March to May. The inability of chemicals to control P. citri successfully and the growing public awareness of the detrimental environmental effects and health risks that are associated with pesticides are pressuring citrus growers to find alternative methods to chemical control. Entomopathogenic nematodes of the Rhabditida order, belonging either to the families Heterorhabditidae or Steinernematidae, have proven to be valuable biocontrol agents of a variety of insect pest species. These nematodes are, however, not yet commercially available in South Africa. Various laboratory bioassays were conducted to determine the potential of entomopathogenic nematodes to control P. citri. Adult female P. citri were screened for susceptibility to six indigenous nematode species. Planococcus citri was found to be most susceptible to Steinernema yirgalemense and Heterorhabditis zealandica, causing 97% and 91% mortality, respectively. Both H. zealandica and S. yirgalemense completed their life cycles inside adult female P. citri. Under optimal conditions, H. zealandica and S. yirgalemense, at an application rate of 170 infective juveniles (IJs) / insect (LD90), were able to control P. citri efficiently with a discriminating dosage of 11(LD50). The water activity (aw) bioassay indicated that S. yirgalemense was two times more tolerant to lower levels of free water than H. zealandica, with aw50 = 0.96 and aw90 = 0.99, compared to H. zealandica with aw50 = 0.98 and aw90 = 1.01. Furthermore, S. yirgalemense proved able to locate and infect P. citri at a faster rate than H. zealandica. Nematode activity was not significantly affected when exposed to 15°C, 20°C and 25°C. Results of the exposure trial also showed that the first 2−4 h post-application was the most decisive time for establishing successful infection of mealybugs. Further experiments were conducted to determine the ability of two polymer products, Zeba® and Xanthan gum, and a surfactant, Nu-Film-P®, to improve nematode application suspensions. Despite not being as effective as Xanthan gum, Zeba® still retarded sedimentation significantly. The addition of 0.02% Xanthan gum did not improve the ability of nematodes to control P. citri at 60% and 80% relative humidity containing H. zealandica and 0.03% Zeba® increased mortality by 14% at 60% RH and by 22% at 80% RH. The same polymer formulation was tested with S. yirgalemense, with mortality being found to have increased by 21% at 60% RH and by 27% at 80% RH. The combined addition of Nu-Film-P® and Zeba® was able to retard sedimentation significantly, increasing the average number of nematodes deposited on 2-cm2 leaf discs. To illustrate those factors that should be taken into consideration before applying nematodes in an integrated pest management (IPM) programme for citrus, the compatibility of H. zealandica and S. yirgalemense with biological control agents and agrochemicals to which they are most likely to be exposed was determined. Bioassays showed the coccinellid beetle, Cryptolaemus montrouzieri, to be susceptible to both nematode species. Beetle larvae proved to be highly susceptible, with H. zealandica obtaining 80%, and S. yirgalemense obtaining 92% control. Adult beetles were found to be twice as susceptible to S. yirgalemense, with 64% mortality recorded, as to H. zealandica, with 30% mortality recorded. Tolerance of H. zealandica and S. yirgalemense infective juveniles to the affect of aqueous solutions of an insecticide (Cyperphos 500 E.C.®), two biopesticides (CryptogranTM and HelicovirTM), and two adjuvants (Nu-Film-P® and Zeba®) on the infectivity and survival of H. zealandica and S. yirgalemense was evaluated. Heterorhabditis zealandica proved to be highly compatible with all products tested. Significant increase in mortality of S. yirgalemense was recorded after 12 h exposure to CryptogranTM, HelicovirTM and Cyperphos 500 E.C.®, and after 6 h exposure to Nu-Film-P®. However, there was no decrease in the ability of S. yirgalemense to infect the insect hosts. Towards selecting the appropriate nematode species for field studies, the ability of S. yirgalemense and H. zealandica to control P. citri was first evaluated under less harsh simulated glasshouse conditions. The ability of both the above-mentioned nematode species to control P. citri, with and without the addition of 0.03% Zeba® and 0.06% Nu-Film-P®, was evaluated in a growth chamber at 75 ± 8% relative humidity and 22°C. All treatments resulted in significantly higher mortality of adult female P. citri than did the control. The addition of 0.03% Zeba® and 0.06% Nu-Film-P® to an H. zealandica and an S. yirgalemense suspension increased resultant mortality from 26% to 30%, and from 34% to 45%, respectively. This increase in mortality was, however, not significant. The ability of this formulation to prolong the ability of S. yirgalemense to infect P. citri and to prolong nematode survival was also evaluated under the same conditions and showed the formulation to improve both infectivity and survival for up to 2–3 h post-application. In the semi-field trial, S. yirgalemense was unable to obtain significant control of P. citri without the addition of 0.03% Zeba® to nematode application suspensions. However, with the addition of 0.03% Zeba® S. yirgalemnse was able to obtain up to 53% control. The study established that the polymer product Zeba® improves the ability of S. yirgalemense to infect P. citri by retarding desiccation and by buffering nematodes from suboptimal environmental conditions. / AFRIKAANSE OPSOMMING: Planococcus citri (Risso) (Hemiptera: Pseudococcidae), die sitrus witluis, is ʼn baie skadelike pes van sitrus in Suid Afrika. Die vermoë van witluise om weerstand teen chemiese middels te ontwikkel, hul kriptiese lewenswyse en die beskermende waslaag wat hul liggame omhul inhibeer gesamentlik en individueel die vermoë van insektisiede om witluis bevolkings te beheer. Chemiese middels verminder ook die natuurlike vyande wat gewoonlik witluis bevolkings beheer voor die sitrus oestydperk in Maart tot Mei. Die onvermoë van chemiese middels om P. citri suksesvol te beheer en verhoogde bewustheid van die publiek rond om die vernietigende omgewings impak en gesondheidsrisiko’s verbonde aan chemiese insek beheer, noodsaak sitrus produsente om alternatiewe beheermetodes te ontwikkel. Entomopatogeniese nematodes, van die orde Rhabditida wat aan die families Heterorhabditidae of Steinernematidae behoort, is bekend as effektiewe biologiese beheeragente van ʼn verskeidenheid insek pes spesies. Hierdie nematodes is egter tans nie kommersieel beskikbaar in Suid- Afrika nie. Om ten einde die vermoë van plaaslike nematode spesies te bepaal om P. citri te beheer, is verskeie biotoetse in die laboratorium uitgevoer. ʼn Vinnige siftings proses is uitgevoer om vas te stel watter plaaslike nematode spesies die hoogste persentasie mortaliteit van P. citri wyfies veroorsaak. Daar is bevind dat P. citri die mees vatbaarste is vir Steinernema yirgalemense en Heterorhabditis zealandica wat 97% en 91% mortaliteit respektiewelik veroorsaak het. Die ontwikkeling van beide H. zealandica en S. yirgalemense na die infektering van volwasse P. citri wyfies is gevolg en daar is bevind dat beide nematode spesies hul lewensiklusse kon voltooi in insek kadawers. Onder optimale toestande was H. zealandica en S. yirgalemense in staat om P. citri effektief te beheer, as hul teen ʼn konsentrasie van 170 infektiewe larwes (JIs) per insek (LD90) toegedien word, met ʼn diskriminerende toedienings dosis van 11 (LD50). ʼn Water aktiwiteit biotoets het gewys dat S. yirgalemense twee keer so verdraagsaam is teenoor laer vlakke van vrye water as wat H. zealandica is met aw50 = 0.96 en aw90 = 0.99, in vergelyking met H. zealandica met aw50 = 0.98 en aw90 = 1.01. Resultate van ʼn blootstellings toets het ook gewys dat S. yirgalemense die vermoë het om P. citri vinniger op te spoor en te infekteer as H. zealandica. Die blootstellings toets was uitgevoer teen 15°C, 20°C en 25°C en daar is bevind dat die aktiwiteit van H. zealandica nie beduidend verhoog het met ʼn verhoging in temperatuur nie. Resultate vir die blootstellings toets het ook gewys dat die eerste 2 tot 4 uur na toediening van nematodes die mees kritieke tyd is om suksesvolle infektering van witluise te bevestig. Verdere eksperimente is uitgevoer om te bepaal of die byvoeging van twee polimeer produkte nl. Zeba® en Xanthan gum en ʼn benatter Nu-Film-P®, nematode toedienings suspensies kan verbeter. Deur 0.02% Xanthan gum by nematode toedienings suspensies te voeg is die vermoë van nematodes om P. citri by 60% en 80% relatiewe humiditeit (RH) te beheer nie beduidend verhoog nie, terwyl die byvoeging van 0.03% Zeba® wel ʼn beduidende verhoging in mortaliteit veroorsaak het. ʼn Suspensie van H. zealandica en 0.03% Zeba® het beheer met 14% by 60% RH en met 22% by 80% RH verhoog. Die invloed van dieselfde polimeer formulasie was ook getoets op S. yirgalemense en mortaliteit het verhoog met 21% by 60% RH en met 27% by 80% RH. Ten spyte daarvan dat “Xanthan gum” nie so effektief was om afsakking van nematodes te verhoed nie, het die byvoeginging van 0.03% Zeba® by toedienings suspensies steeds ʼn beduidende invloed gehad. Die gekombineerde byvoeging Nu-Film-P® en Zeba® was in staat om die gemiddelde aantal nematodes gedeponeer op 2-cm2 blaar skyfies te verhoog. Om te wys watter faktore in ag geneem moet word voor EPNs as deel van ʼn geïntegreerde pes beheer program toegedien word, is die verenigbaarheid van H. zealandica en S. yirgalemense vir biologiese beheer agente en landbouchemikalieë, waaraan hulle heel waarskynlik blootgestel gaan word, bepaal. Biotoetse het gewys dat die liewenheersbesie, Cryptolaemus montrouzieri, vatbaar is vir beide nematode spesies. Die larwale fase was hoogs vatbaar met mortaliteit van 80% en 92% verkry deur die toedeining van H. zealandica en S. yirgalemense respektiewelik. Daar is ook bepaal dat volwasse besies twee maal so vatbaar is vir S. yirgalemense wat 64% mortaliteit veroorsaak het, as vir H. zealandica met 30% mortaliteit aangeteken. Verdraagsaamheid van IJs van H. zealandica en S. yirgalemense met oplossings van ʼn insektisied (Cyperphos 500 E.C.®), twee bio-plaagdoders (CryptogranTM en HelicovirTM), en twee byvoegmiddels (Nu-Film-P® en Zeba®), vir infektiwiteit en oorlewing is bepaal. Resultate het gewys dat H. zealandica hoogs verenigbaar is met alle produkte wat getoets is. ʼn Beduidende verhoging in mortaliteit van S. yirgalemense is aangeteken na 12 ure se blootstelling aan CryptogranTM, HelicovirTM en Cyperphos 500 E.C.®, en na 6 ure se blootstelling aan Nu-Film-P®. Resultate het egter ook gewys dat die vermoë van S. yirgalemense om om gashere te infekteer nie deur beinvloed word nie. Om ten einde te bepaal watter een van H. zealandica of S. yirgalemense die beter isolaat sou wees om te gebruik in veldproewe, is hul vermoë om P. citri te beheer eers evalueer onder minder ongunstige gesimuleerde glashuis toestande. Die vermoë van beide nematode spesies om P. citri te beheer is bepaal in ʼn groeikamer by 75 ± 8% (RH) met en sonder die byvoeging van 0.03% Zeba® en 0.06% Nu-Film-P®. Mortaliteit verkry deur alle behandelings was beduidend hoër as die kontrole. Deur 0.03% Zeba® en 0.06% Nu-Film-P® by toedienings suspensies van H. zealandica en S. yirgalemense te voeg is die gevolglike mortaliteit van P. citri verhoog van 26% na 30% en van 34% na 45%, respektiewelik. Hierdie verhoging in mortaliteit was egter nie beduidend nie. Die vermoë van die bo-genoemde formulasie om oorlewing van S. yirgalemense en infeksie tydperk van P. citri te verleng was bepaal onder dieselfde toestande en daar is gevind dat die formulasie beide die infektiwiteit en oorlewing van nematodes met 2 tot 3 uur na toediening verleng het. Tydens die semi-veldproef was S. yirgalemense nie in staat om beduidend hoër mortaliteit van P. citri te verkry, in vergelyking met die kontrole, sonder die byvoeging van 0.03% Zeba® by toedienings suspensies nie. Met die byvoeging van Zeba® is daar tot 53% beheer verkry. Die studie het onweerlegbaar gewys dat die polimeer produk Zeba® die vermoë van S. yirgalemense om P. citri te infekteer verbeter deur die uitdroging van nematodes te vertraag en deur hul te beskerm teen ongunstige omgewings toestande.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--Stellenbosch University, 2008. / The widespread ecological impacts of overgrazing by livestock within the Succulent Karoo have received considerable attention. Literature shows communal and commercial rangelands have been thoroughly studied, and vegetation responses have been investigated in an attempt to understand the effects of overgrazing. Regarding animal species, literature is in short supply. In a one-year study of small mammal assemblages, the effect of the rangelands, and subsequently vegetation, on small mammal assemblages was examined, as well as the effects on number of occupied, unoccupied and collapsed burrows. This study shows that vegetation composition differs between rangelands, with a greater perennial shrub cover on the communal rangelands and a greater perennial succulent cover on commercial rangelands, consequently creating different habitats for animal assemblages. This study supports the notion of small mammal composition relating to vegetation structure, with certain species being impacted by heavy grazing. Four small mammal species were found in greater abundances on commercial rangelands, with one being exclusive, while communal rangelands were exclusively occupied by three nocturnal species. Diet and habitat requirements are the most important factors regarding species occurrence. With small mammal species composition differing between rangelands, and species richness not being affected by rangeland type, this study illustrates that the disappearance of certain species may arise without these different rangelands. This could result in reduced species richness, and thus diversity being lost. Regarding species present on both rangelands, no differences were observed in body mass, body size or body condition. Despite no differences found in body condition, calculating a body condition index is a good method for investigating how a species is coping within an environment. The proportion and number of occupied and collapsed burrows can be seen as a measure of trampling effect. It was expected for grazing intensity, as well as vegetation changes, to affect the occurrence of such burrows. This study showed differences between the communal and commercial rangelands as negligible. As expected, numbers of burrowing small mammal species were negatively correlated with numbers of collapsed burrows. However, a lack of consistency deemed this result unimportant. Results show that the effects of overgrazing on small mammal populations are complex and require more attention if to be fully explained. This study provides insights into the effects of land use on small mammals and burrow numbers, which have implications for the conservation of these species within arid regions.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--Stellenbosch University, 2008. / This thesis examines the role of agricultural activity in the process of invasion of west coast renosterveld fragments by annual alien grass species. This highly endangered vegetation type has less than 5% remaining, it is vital to understand the mechanisms allowing invasion of annual alien grasses in order to effectively prevent the loss of the many rare and endemic species found in west coast renosterveld. This study was divided into three major components. Firstly the distribution of indigenous and alien plant species in relation to fence lines, separating active agricultural fields from untransformed vegetation, was described. Regression analysis was used to test for relationships between distances from agricultural fields and soil physical and chemical characteristics in natural vegetation. Cover by annual alien invasive grasses in untransformed vegetation decreased significantly with distance away from agricultural land. Secondly alien and indigenous grass seed banks were sampled along the transects, at the same sites, in order to establish whether the seed banks correlated with above ground cover. Results varied among sites and seed banks were correlated with the vegetation cover at only one site. It appears that there are a multitude of factors determining the distribution of annual alien grass cover. Thirdly a greenhouse experiment established the role that nitrogen plays in the success of the alien grass Avena fatua. This species was grown in competition with three indigenous species, an annual forb (Dimorphotheca pluvialis), a geophyte (Oxalis purpurea) and an indigenous perennial grass (Tribolium uniolae) at three levels of soil nitrogen. The geophyte was largely unaffected, while growth of the annual and indigenous perennial grasses was negatively affected by competition with A. fatua. Nitrogen did not seem to affect competitive interactions. Management of these renosterveld patches, in order to conserve them effectively, will require a multi-faceted approach, including prevention of further invasion and removal of invasive grasses already present.

Thesis (PhD (Conservation Ecology and Entomology))--University of Stellenbosch, 2011. / AFRIKAANSE OPSOMMING: Min aandag is al gegee aan biogeomorfologiese interaksies in glasiale en periglasiale omgewings. Nietemin is hierdie interaksies, wat op die skeidingsvlak tussen ekologie en geomorfologie fokus, baie belangrik in hierdie omgewings, waar organismes in noue verband met die abiotiese omgewing saamleef. In hierdie tesis bestudeer ek die interaksies tussen die vaskulêre plantspesies met die hoogste voorkoms op sub-Antarktiese Marion Eiland, Azorella selago Hook. (Apiaceae), en die omringende geomorfologiese landskapsvorme, -prosesse en meettegnieke. Verder verskaf die tesis voorstelle om toekomstige geïntegreerde biogeomorfologiese navorsing te vergemaklik. Om die gevolge van A. selago-plante vir sedimentbeweging en -verspreiding te verstaan, het ek die verspreiding van sedimentgroottes om hierdie plante gemeet deur middel van 'n kombinasie van fotografiese analise-metodes. Deur as sedimentbewegingsobstruksies te dien, het plante 'n waarneembare effek op die omringende sedimentverdeling. Dit is veral belangrik om hierdie interaksies tussen A. selago en sy omgewing te verstaan in die lig van onlangse klimaatsverandering op die eiland, omdat sedimentgrootte belangrike grondeienskappe soos waterretensiekapasiteit en vriesgevoeligheid beïnvloed. Om die effek wat A. selago plante op die omringende mikroklimaat het beter te verstaan, is die kleinskaalse variabiliteit in grondtemperature om A. selago plante bestudeer. Grootskaalse grondligting as gevolg van fors is gemeet, ten spyte van relatief ligte forseienskappe. Dit dui daarop dat naaldys ook by temperature bo -2°C kan vorm. Wintergrondtemperature aan die oostekant van plante was effens laer en minder veranderlik as aan die westekant van plante, waarskynlik as gevolg van laer windsnelhede en/of sneeu wat ophoop aan die oostelike, lykant van plante. Die resultate benadruk dat A. selago plante 'n belangrike rol speel in die verandering van mikroklimate en dat dit belangrik is om die gevolge van sulke veranderings, soos die skep van mikrohabitatte vir grondorganismes, te verstaan. Daar word vermoed dat positiewe plantinteraksies negatiewe interaksies oorheers in omgewings met hoe abiotiese druk. Gevolglik wys ek dat daar 'n positiewe verband bestaan tussen A. selago plante en saailinge van beide A. selago self, asook van die meerjarige gras Agrostis magellanica Lam. (Poaceae). Ek stel voor dat beide plante en klippe sade, wat deur wind, reenval en/of afdraande sedimenttransportering as gevolg van vriesprosesse vervoer word, opvang. Verder dui verhoogde A. selago saailinggetalle om plante, maar nie om klippe nie, daarop dat plante een of ander biologiese voordeel aan A. selago saailinge bied. Dit is bekend dat die verspreidingspatrone van plantspesies as gevolg van abiotiese stresgradiente varieër. Met hierdie bevinding in gedagte, is moontlike faktore verantwoordelik vir A. selago saailinggetalle en -verspreidingspatrone, soos hoogte bo seespieël en substraatbedekking, bestudeer. Alhoewel dit wil voorkom asof daar 'n verband tussen saailinggetalle en hoogte bo seespieël is, is saailinggetalle en verpreidings meestal afhanklik van ongemeette perseel-spesifieke eienskappe. Plante kan die omringende geomorfologie beïnvloed, maar ook geomorfologiese meettegnieke. Om die potensiaal van kosmogeniese dateringsmetodes as geomorfologiese hulpmiddels in fellfield habitatte te verken, is die akkumulasietempo van die kosmogeniese isotoop ¹ºBe onder en langs 'n A. selago plant bepaal. Die resultate dui daarop dat ¹ºBe nie ten volle in die grondprofiel behoue bly nie en verskeie potensiële redes word bespreek. Verder dui die resultate daarop dat ¹ºBe konsentrasies in fellfield habitatte versigtig geïnterpreteer moet word, aangesien A. selago plante effektief ¹ºBe opvang in hulle grondryke kern. Om vordering in biogeomorfologie te vergemaklik, is dit belangrik om bewus te wees van die verskillende metodes wat geomorfoloë en ekoloë volg. Ekologiese benaderings is dikwels op strenger statistiese tegnieke gebaseer, terwyl geomorfoloë eerder fokus op 'n meer beskrywende benadering en teoretiese beredenering. Ek verduidelik hoekom die twee velde sulke uiteenlopende benaderings volg, benadruk moontlike struikelblokke en verskaf voorstelle om samewerking te vergemaklik. / ENGLISH ABSTRACT: There are few scientific publications that relate to biogeomorphological interactions in glacial and periglacial environments. Interactions that focus on the interface between ecology and geomorphology are very important in these environments, as a tight coupling often exists between organisms and their abiotic surroundings. In this thesis the interactions between the dominant vascular cushion plant species on sub-Antarctic Marion Island, Azorella selago Hook. (Apiaceae), and the surrounding geomorphological landforms, processes and measuring techniques were studied. In addition, the thesis provides suggestions to facilitate future integrated biogeomorphological research. To understand the consequences of A. selago cushions for substrate movement and sorting, the grain size distribution of sediment surrounding these cushions was quantified using a combination of image analysis approaches. Through obstructing frost-related sediment transport, A. selago cushions are shown to affect the grain size sorting of the surrounding sediment. Particle size affects soil properties such as water-holding capacity and frost susceptibility. It is therefore important to understand the interactions between A. selago cushions and sediment distributions, especially in the light of recent warming and drying on the island. Fine scale variability in soil temperature parameters was studied around cushions to improve understanding on how A. selago affects the surrounding soil microclimate. Despite the mild frost climate, extensive frost heave occurred in the study area, indicating that needle ice forms above the previously suggested required temperature of -2°C. Lower and less variable winter temperatures were found on eastern than on western cushion sides, probably as a result of lower wind speeds or leeside snow accumulation on eastern cushion sides. These research findings highlight the importance of A. selago cushions in modifying site microclimates. Such modifications could have important potential consequences, such as providing microhabitats for soil microorganisms and seedlings. Positive plant interactions have been suggested to dominate over negative interactions in environments with high abiotic stress. Positive associations were found between A. selago and both its own seedlings and those of the perennial grass, Agrostis magellanica Lam. (Poaceae) on Marion Island. It is suggested that both cushions and rocks trap seeds dispersed by wind, runoff and/or downslope sediment transport through frost creep. In addition, increased A. selago seedling numbers around cushions, but not around rocks, suggest that cushions provide a biological nurse effect to seedlings of their own kind. Plant species' distributions have been known to vary in response to abiotic stress gradients. In light of this, determinants of A. selago seedling distributions and abundance, such as altitude and substrate cover, were explored. Although there appears to be some altitudinal trend, seedling distributions and abundance patterns were largely attributed to unaccounted variation between sites. Plants can affect the surrounding geomorphology, but also geomorphological measuring techniques. To explore the potential of cosmogenic dating techniques as geomorphological tools in fellfield habitats, accumulation rates of the cosmogenic isotope ­¹ºBe were assessed underneath and adjacent to an A. selago cushion. The results show that ¹ºBe is not fully retained in the soil profile and various reasons are discussed. Furthermore, the results suggest that ¹ºBe concentrations should be interpreted cautiously in fellfield habitats, as A. selago cushions effectively intercept the isotope in their soil-rich core. To facilitate the integration of geomorphological and ecological principles, as was attempted in this thesis, it is important to understand the philosophies behind the different research approaches that ecologists and geomorphologists employ. Ecologists often employ a more statistics-based approach, whereas geomorphologists focus on a more descriptive approach and reasoning based on established theories. I attempt to explain why the two fields follow such different approaches, highlight some potential challenges and provide suggestions to facilitate progress in the interdisciplinary field of biogeomorphology.

Thesis (MScAgric (Conservation Ecology and Entomology))--Stellenbosch University, 2011 / ENGLISH ABSTRACT: Climate change will alter both temperature and moisture availability in the future and therefore will likely affect vector borne disease prevalence. Organisms faced with changes in weather can respond in a variety of ways and this complicates any predictions and inferences for these organisms with climate change. Cause-and-effect links between climate change, insect vector responses, and changes in risk of disease transmission are poorly established for most vector borne diseases. Tsetse (Diptera, Glossinidae) are important vectors of trypanosome parasites posing a major threat to human health and socio-economic welfare in Africa. Water balance plays an important role in determining activity patterns, energy budgets, survival and population dynamics and, hence, geographic distribution and abundance of insects. Glossina species occupy a wide range of habitats in Africa and are notable for their desiccation resistance in xeric environments. Yet, whether or not the different species, subgroups or ecotype groups differ in susceptibility to changes in weather remain undetermined. The first main focus of my thesis was to test the effects of climate change on water balance traits (water loss rate, body water content and body lipid content) of adult tsetse flies. Four species from xeric and mesic habitats were exposed to a range of temperature (20 – 30 °C) and relative humidity (0 – 99 %) combinations. Water loss rates were significantly affected by measurement treatments, while body water content, body lipid content and mass were less affected and less variable across treatment combinations. The results provide support for mass-independent inter- and intra-specific variation in water loss rate and survival times. Therefore, water balance responses to variation in temperature and relative humidity are complex in Glossina, and this response varies within and among species, sub-groups and ecotypes in terms of magnitude and the direction of effect change. Secondly, I apply a mechanistic distribution model for G. pallidipes to predict potential population responses to climate change. I validate the mechanistic model (NicheMapperTM) results spatially and temporally using two methods. Both tests of the model showed that NicheMapper‟s predicted resting metabolic rate has great potential to capture various aspects of population dynamics and biogeography in G. pallidipes. Furthermore, I simulate the effect of phenotypic plasticity under different climate change scenarios and solve for the basic reproductive number of the trypanosomiasis disease (R0) under a future climate scenario. This integrated thesis provides strong evidence for a general decrease in optimal habitat for G. pallidipes under future climate change scenarios. However, it also provides strong support for a 1.85 fold increase in R0 based on changes in biting frequency as a result of higher predicted metabolic rates in the future. This might suggest that the reduction in optimal habitat could be outweighed by the increase in R0. The results demonstrate that an understanding of the physiological mechanism(s) influencing vectors of disease with climate change can provide insight into forecasting variation in vector abundance and disease risk. / AFRIKAANSE OPSOMMING: Die invloed van klimaatsverandering op die temperatuur en vog beskikbaarheid mag moontlik insek-oordraagbare siektes in the toekoms beïnvloed. Organismes wat verandering in klimaat ervaar kan op verskillende maniere reageer en daarom is voorspelling en afleidings van die reaksies op klimaatsverandering nie eenvoudig nie. Boonop is die verband tussen klimaatsverandering, insek reaksies en veranderinge in die oordragsrisiko van siektes onbekend vir die meeste insekoordraagbare siektes. Tsetse (Diptera: Glossinidae) is belangrike draers van trypanosoom parasiete wat 'n bedreiging inhou vir mensegesondheid en sosio-ekonomiese welsyn in Afrika. Waterbalans speel 'n belangrike rol in die energiebondel samestelling, aktiwiteitspatrone, oorlewing en populasie dinamika van insekte en, dus, die geografiese voorkoms en verspreiding van insekte. Glossina spesies kom in 'n verskeidenheid habitatte in Afrika voor en is bekend daarvoor dat hulle weerstand bied teen uitdroging in droё habitatte. Maar, die mate waartoe die verskillende subgroepe, ekotiepegroepe en spesies kwesbaar is vir klimaatsverandering, is steeds onbekend. Die eerste hooffokus van my tesis was om die uitwerking van klimaatsverandering op waterbalansrelevante uitkomste (tempo van waterverlies, waterinhoud en vetinhoud) van volwasse tsetse vlieё te bestudeer. Vier spesies van droë en klam habitatte is aan verskillende kombinasies van temperatuur (20 – 30 °C) en relatiewe humiditeit (0 – 99 %) blootgestel. Die tempo van waterverlies is betekenisvol deur die verskillende toetskombinasies beïnvloed, terwyl die waterinhoud, vetinhoud en liggaamsmassa tot 'n minder mate beïnvloed is en minder gevarieer het tussen die toetskombinasies. Die resultate toon bewyse vir gewigs-onafhanklike inter- en intraspesie variasie in waterverlies tempo‟s en oorlewingstyd. Die waterbalans uitkomste op variasie in temperatuur en relatiewe humiditeit is dus ingewikkeld in Glossina, en dit varieer binne en tussen spesies, subgroepe en ekotiepe in terme van die graad en rigting van effek verandering. Tweedens pas ek 'n meganistiese verspreidingsmodel toe vir G. pallidipes om die moontlike populasiereaksies met klimaatsverandering te voorspel. Ek toets die antwoorde van die model (NicheMapperTM) oor tyd en skaal op twee verskillende maniere. Beide toetse het aangedui dat die NicheMapper voorspelde rustende metaboliese tempo die verskillende aspekte van G. pallidipes populasie dinamika en biogeografie goed beskryf. Ek simuleer die uitkomste van die fenotipiese veranderbaarheid van G. pallidipes onder „n verskeidenheid klimaatsverandering-uitkomste, en los „n model van die basiese ommekeer van trypanosomiasis (R0) op onder 'n klimatsverandering situasie in die toekoms. Hierdie geïntegreerde tesis toon sterk bewyse dat die optimale habitat van G. pallidipes verminder met klimaatsverandering. Dit toon egter ook bewyse vir 'n 1.85 keer toename in R0 gebasseer op 'n verhoging in die frekwensie van bytgeleenthede weens die hoër voorspelde metaboliese tempo van die vlieë in die toekoms. Laasgenoemde stel voor dat die afname in optimale habitat moontlik deur 'n toename in R0 oorheers sal word. Die resultate demonstreer dat beter begrip van die fisiologiese meganisme(s) wat parasiet-draers beïnvloed verdere insig kan voorsien in die toekomstige voorspelling van draer teenwoordigheid en siekte waarskynlikheid.

Thesis (PhD (Conservation Ecology and Entomology))--Stellenbosch University, 2008. / The mutual association between honeydew foraging ants and vine mealybugs in vineyards is detrimental to the biological control of the vine mealybug Planococcus ficus (Signoret). This study investigated the relationship between ants, vine mealybugs and their parasitoids to improve biological control of the vine mealybug. The investigation was carried out during two consecutive growing seasons (2005-2006 and 2006-2007) in two major wine grape growing areas of the Western Cape Province, Simondium (two farms) and Breede River Valley (one farm). A presence – absence cluster sampling system was used on a biweekly basis throughout both growing seasons from October to February on each of the farms. Additionally, yellow delta traps with vine mealybug pheromone, were used to catch parasitoids in vineyards. Prior to harvest, economic damage to grape bunches was assessed using a 0-3 damage rating index. Three ant species, Anoplolepis steingroeveri (Forel), Crematogaster peringueyi Emery and Linepithema humile (Mayr) foraged mainly on vine stems during both seasons, relative to other plant parts. Vine mealybugs of all stages were found on all sampling dates. Three species of primary parasitoids attacked the vine mealybug, including Anagyrus sp. near pseudococci (Girault), Coccidoxenoides perminutus (Timberlake) and Leptomastix dactylopii Howard. Bunch damage was significantly different between seasons in the Breede River Valley but not in Simondium. There was a negative linear relationship between ants and parasitoid activity in all vineyards. Spatial Analysis by Distance IndicEs (SADIE) was used to analyse spatial distribution of ants and parasitoids and ArcView, with its extension, Spatial Analyst, were used to map the gap, patch and local association indices where significant association and disassociation occurred. A significant association was found between C. peringueyi and parasitoids and L. humile and parasitoids. There was a significant disassociation between L. humile and C. peringueyi and between A. steingroeveri and C. peringueyi indicating interspecific hostility.

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) is a devastating pest of pome fruit in temperate regions of the world. Control of this pest, previously involved the extensive use of broad-spectrum insecticides. However, concerns over human safety, environmental impact, widespread dispersal of resistant populations of codling moth and the sustainability of synthetic pesticides in agroecosystems, has encouraged the development and use of alternative environmentally-friendly pest management technologies including the use of entomopathogenic nematodes. These nematodes are lethal pathogens of insects and belong to the families Steinernematidae and Heterorhabditidae, and are ideal candidates for incorporation into the integrated pest management programme currently being developed for residue-free pome fruit production in South Africa. The biological and ecological factors pertaining to the successful use of these nematodes for the control of codling moth were investigated in this study. Their use for bin-disinfestations was evaluated, focusing on the optimum handling conditions to ensure the survival and subsequent efficacy of the nematodes. The study proved that the local isolate SF41 of Heterorhabditis zealandica Poinar 1990 could be used for successful bin-disinfestation. The use of the same nematode isolate was also investigated for the disinfestation of mulch layers of diapausing codling moth larvae. An insect containment device which allowed for direct trial efficacy evaluation was identified and ecological factors pertaining to the successful use of nematodes for mulch disinfestation were investigated. The biological control potential of local nematode isolates, which had previously never been tested against codling moth larvae, was investigated in the laboratory under conditions as can be expected during orchard applications. The efficacy of the selected isolates was confirmed in field experiments. Innovative insect containment methods for above-ground trial efficacy evaluation in the field were investigated. Desiccation proved to be the most limiting factor to the survival and subsequent efficacy of the nematodes during field applications in temperate regions. The effect of low moisture levels on H. zealandica’s efficacy to control diapausing codling moth larvae was subsequently investigated and a starch-based formulation was further tested to overcome the issue of desiccation. Conclusive results indicated that there were several biological and ecological factors influencing the survival of nematodes and illustrated how these factors could be manipulated to overcome these issues and thereby ensure the efficacy of treatments. This is the first report of its kind to comprehensively investigate the use of South African entomopathogenic nematodes for the control of diapausing codling moth larvae and all results emanating from the study can be integrated into a framework for the commercial use of these nematodes in this regard in future. / AFRIKAANSE OPSOMMING: Kodlingmot, Cydia pomonella (L.) is ‘n ernstige sleutelplaag in appel- en peerboorde in gematigde klimaats gebiede wêreldwyd. In die verlede is hoofsaaklik breëspektrum insektedoders gebruik vir die beheer van hierdie plaaginsek. Maar, kommer oor veiligheid vir die mens, impak op die omgewing, verspreiding van weerstandbiedende populasies van kodlingmot en beperkte volhoubaarheid van sintetiese plaagdoders het die ontwikkeling en gebruik van alternatiewe plaagbeheer tegnologieë, insluitend die gebruik van entomopatogeniese nematodes, genoodsaak. Entomopatogeniese nematodese horende tot die families Steinernematidae en Heterorhabditidae, is ideale kandidate vir insluiting in die geïntegreerde plaagbestuur programme wat huidiglik ontwikkel word vir gebruik in plaaslike boorde met die uiteindelike doel om residu-vrye vrugte te produseer. In hierdie studie word die biologiese en ekologiese faktore bestudeer wat die sukses van ‘n nematode-toediening gemik op kodlingmot beïnvloed. Hierdie studie het bewys dat die lokale SF41 isolaat van Heterorhabditis zealandica Poinar 1990 gebruik kan word om vrugtekratte te disinfesteer van kodlingmot. Die gebruik van dieselfde isolaat vir die disinfestasie van deklae is ook ondersoek. ‘n Metode van insek-inkamping is ook ontwikkel wat die evaluering van toedienings vergemaklik en meer effektief maak. Die omgewings-toestande wat ook bydrae tot die oorlewing en gevolglike sukses van ‘n toediening is ook ondersoek. Die biologiese beheer potensiaal van ‘n paar lokale isolate wat nog nooit voorheen teen kodlingmot getoets is nie, is ook bestudeer. Die isolate se effektiwiteit is ook bevestig in veldproewe en insek-bekampings metodes wat meer van toepassing is vir bogrondse plaaginsekte is ook geïdentifiseer. Resultate dui daarop dat vogverlies en gevolglike uitdroging van nematodes die grootste beperkende faktor is vir hierdie tipe toedienings in gematigde gebiede en ‘n stysel-gebaseerde formulasie is dus ondersoek om hierdie probleem te oorkom. Die uiteindelike gevolgtrekking van die studie was, dat alhoewel daar verskeie biologiese en ekologiese faktore is wat die oorlewing van nematodes beperk, daar tog verskeie maniere is om hierdie faktore te manipuleer en sodoende te oorkom, wat bydrae tot die uiteindelike sukses van ‘n toediening. Hierdie is die eerste studie wat werklik die praktiese gebruik van lokale entomopatogeniese nematodes vir die beheer van kodlingmot ondersoek en alle bevindinge kan geïntegreer word in toekomende riglyne vir die kommeriële gebruik van nematodes vir die beheer van kodlingmot.

Thesis (PhD (Conservation Ecology and Entomology))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: There is a growing appreciation of the importance of non-timber forest products (NTFPs) and the role they play in the socio-economic wellbeing of rural communities and other stakeholders. Harvest systems to ensure sustainable harvesting are largely still lacking and overutilisation is of growing concern worldwide. In this study the science needed to underwrite management for sustainable use of NTFPs was explored. This was done using case studies of three different products harvested from natural forest in the southern Cape, South Africa viz. fern (Rumohra adiantiformis) fronds (leaves) as greenery in the florist industry, medicinal tree bark, and the corm (stem) of the geophyte Bulbine latifolia for medicinal use. The research approach enabled insight into the complexities of developing harvest systems for NTFPs, the input and expertise required to conduct applied research, and the variation in approach required for different products and plant growth forms. The study on R. adiantiformis showed that the adaptive management approach can be followed effectively with the development of harvest prescriptions for a species. Goalorientated, long-term monitoring, assessing harvest impact on the resource and natural fluctuations in population dynamics, are essential to verify that harvest prescriptions are sound and ecologically sustainable. However, if all relevant aspects are covered, the input required to develop and refine harvest systems through such monitoring may be extensive. Experimental stripping of medicinal tree bark showed that species respond differently to wounding, in terms of both bark regrowth and susceptibility to fungal and insect damage. The conceptual model and decision tree developed, demonstrated that tree response to wounding could be used effectively when choosing a management system for bark harvesting, and in informing prescriptions for strip harvesting. The proposed harvest system for the target species, as well as alternative options to meet the demand for bark can be successfully integrated with the existing multiple-use forest management system in the southern Cape. The study of the ecology and dynamics of B. latifolia showed that the species has a complex population dynamics and is abundant on the fynbos/forest ecotone, where it is associated with dry scrub forest communities. Although regeneration is sound, it has a slow rate of renewal in terms of corm diameter and length growth, limiting its harvest potential. The difference between ecotone and forest populations – in terms of population dynamics, plant demography and regeneration phenology – requires that consideration be given to differential harvest prescriptions for ecotone and forest populations. It was concluded that a simple generic process that provides for research to be focused on the relevant fields can be followed effectively with the development of harvest systems for NTFPs. However, sustainability also has a socio-economic and political dimension, further influenced by institutional arrangements. Considering the wide range of NTFPs used, socioeconomic circumstances and the dependence of rural communities on natural resources, a major challenge awaits forest managers in South Africa to develop harvest systems for sustainable use. Policy and decision makers need to appreciate the scientific skills and expertise, and financial resources required to realise this. / AFRIKAANSE OPSOMMING: Die belangrikheid van bosprodukte anders as hout en die rol wat dit in die sosio-ekonomiese welstand van landelike gemeenskappe en ander belanghebbendes kan speel, word toenemend besef. Oesstelsels om standhoudende benutting te verseker is grootliks afwesig en oorbenutting is wêreldwyd ’n toenemende bron van kommer. In hierdie studie word die wetenskaplike insette benodig om oesstelsels vir nie-houtbosprodukte te onderskryf, betrag. Dit is gedoen aan die hand van gevallestudies van drie bosprodukte wat uit natuurlike woud in die Suid-Kaap, Suid-Afrika, benut word, naamlik die blare van die varing Rumohra adiantiformis vir blommerangskikkings, medisinale boombas en die stam van die geofiet Bulbine latifolia vir medisinale doeleindes. Die navorsingsbenadering laat toe om insig te bekom in die kompleksiteit met die ontwikkeling van oesstelsels vir nie-houtbosprodukte, die insette en kundigheid benodig vir toegepaste navorsing, en die verskillende benaderings met verskillende bosprodukte en plantgroeivorms. Die studie oor R. adiantiformis dui aan dat ’n aanpasbare bestuursbenadering suksevol gevolg kan word met die ontwikkeling van oesvoorskrifte vir ’n spesie. Doelgerigte langtermynmonitering om die impak van inoesting op die bron en natuurlike fluktuasies in populasiedinamika te bepaal, is noodsaaklik om te kan aandui of oesvoorskrifte ekologiese standhoudendheid verseker. Die insette benodig om oesstelsels te ontwikkel en deur langtermynmonitering te verfyn, kan egter aansienlik wees. Eksperimentele basstroop dui aan dat boomspesies verskillend reageer op basverwydering in terme van bashergroei en vatbaarheid vir insek- en swamskade. ’n Konsepmodel en vloeidiagram vir besluitneming is ontwikkel en dui aan dat ’n boomspesie se reaksie op basverwydering effektief aangewend kan word in die keuse van ’n oesstelsel en die ontwikkeling van voorskrifte vir strookbenutting. Die voorgestelde oesstelsel vir die teikenspesies en ander alternatiewe om in die behoefte vir bas te voorsien, kan doeltreffend geintegreer word met die bestaande meervoudige-benutting woudbestuurstelsel in plek in die Suid-Kaap. Die studie oor die ekologie en dinamika van B. latifolia dui aan dat die soort goed verteenwoordig is in die fynbos/woud-ekotoon, dat dit geassosieer is met droë struikwoud, en ’n komplekse populasiedinamika het. Alhoewel dit goed verjong, het dit, gemeet aan stamdeursnee- en -lengtegroei, ’n lae groeitempo wat die benuttingspotensiaal van die spesie beperk. Die verskille tussen ekotoon- en woudpopulasies – in terme van populasiedinamika, demografie en reproduksiefenologie – vereis dat oorweging geskenk word aan verskillende oesvoorskrifte vir ekotoon- en woudpopulasies. ’n Eenvoudige, generiese proses wat verseker dat navorsing gefokus is op die toespaslike velde kan suksesvol gevolg word met die ontwikkeling van oesstelsels vir niehoutbosprodukte. Standhoudendheid het egter ook ’n sosio-ekonomiese en politieke komponent wat verder beinvloed word deur institusionele strukture. Inaggenome die wye verskeidenheid van nie-houtbosprodukte wat benut word, sosio-ekonomiese omstandighede en die afhanklikheid van landelike gemeenskappe van natuurlike hulpbronne, is die ontwikkeling van oesstelsels vir standhoudende benutting ’n groot uitdaging vir woudbestuursinstansies. Beleidmakers en besluitnemers moet ’n waardering ontwikkel vir die wetenskaplike kundigheid en kennis, en finansiële hulpbronne, wat benodig word om dit te bewerkstellig.

Thesis (PhD (Conservation Ecology and Entomology))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Natural and semi-natural ecosystems and human communities worldwide are under siege from a growing number of destructive invasive alien species. Alien species are those whose presence in an area is due to intentional or accidental introduction as a result of human activities. Some alien species become invasive, and some cause tremendous destruction to the ecosystem and their stability, but we do not yet understand fully the many factors that determine the levels of invasiveness in alien species. However, management of alien plants requires a detailed understanding of the factors that make them invasive in their new habitat. The aim of this study was to explore in detail the processes and potential for invasion of Schinus molle (Peruvian pepper tree) into semiarid savanna in South Africa and to examine the potential for this species to invade further in these ecosystems, and in other South African biomes. In this thesis I explored the patterns and processes of invasion of S. molle in semiarid savanna using small-scale experiments to investigate physical and ecological barriers to invasion that prevent or accelerate the invasion of this species. I examined factors such as pollination; seed production; seed dispersal; seed predation and viability, all known to contribute to invasiveness. I highlighted the critical role of microsite conditions (temperature, humidity, water availability) in facilitating S. molle seedling establishment in semi-arid savanna and demonstrated that microsite type characteristics need to be considered for management and monitoring of the species in South Africa. I demonstrated the ability of S. molle to out-compete indigenous woody plants for light and other resources and also showed that disturbance of natural ecosystems was not a prerequisite for invasion, although human activities such as tree planting have played a major role in disseminating this species in South Africa. Predicting the future distribution of invasive species is very important for the management and conservation of natural ecosystems, and for the development of policy. For this reason, I also assessed the present and potential future spatial distribution of S. molle in South Africa by using bioclimatic models and a simulation-based spread model. I produced accurate profiles of environmental conditions (both biophysical and those related to human activities) that characterize the planted and naturalized ranges of this species in South Africa, by linking species determinants, potential habitat suitability and likely spread dynamics under different scenarios of management and climate change. All those components provided insights on the dynamics of invasions by fleshy-fruited woody alien plants in general, and on S. molle invasions in South Africa in particular. I developed a conceptual model that described S. molle population dynamics leading to an understanding of the processes leading to the invasive spread of this species in South Africa. This work also emphasized the need for policy review concerning the invasive status of S. molle in South Africa, and recommendations are made for future research. / AFRIKAANSE OPSOMMING: Die natuurlike and half-natuurlike ekosisteme sowel as menslike gemeenskappe wereldwyd word bedreig deur ‘n groeiende hoeveelheid indringerplantspesies. Indringerplantspesies (daardie spesies wie se teenwoordigheid toegeskryf kan word aan opsetlike of toevallige inbringing deur menslike toedoen) is ‘n bedreiging nie net vanweë die massiewe verwoesting van die ekosisteme en ekosisteemstabilitiet nie, maar ook omdat ons nog nie ten volle verstaan hoe hulle van skaars in hul natuurlike omgewing tot dominant in hul nuwe habitat gaan nie. Bestuur van indringer plante vereis ’n begrip van biologise en ekologiese faktore wat lei tot hulle indringing in die nuwe habitat. Die primêre doel van hierdie studie was om in detail uit te vind wat die prosessesse en potensiaal is vir die indringing van S. molle (die Peruviaanse peper boom) in droë savanna en om indringingspatrone in droë savanna met huidige en potensieële toekomstige patrone in ander Suid-Afrikaanse biome te vergelyk. In hierdie tesis ondersoek ek die patrone en prosesse wat verband hou met die indringing van S. molle in droë savanna deur gebruik te maak van kleinskaalse eksperimente om fisiese en ekologise hindenisse te ondersoek wat indringing van S. molle in Suid-Afrika voorkom of versnel. Dit sluit faktore in wat bekend is om by te dra tot indringing van plant spesies, soos bestuiwing, saadproduksie, saadpredasie en kiemkragtigheid. Ek het die kritieke rol beklemtoon van mikroomgewingskondisies (temperatuur, humiditeit, waterbeskikbaarheid) in die fasilitering van S. molle saailingvestiging in droë savanna en het gedemonstreer dat die tipe mikroomgewingskarakteristieke in ag geneem moet word by betuur en monitering van die verspreiding van S. molle in Suid-Afrika. Ek het die vermoë van S. molle om inheemse plante te uitkompeteer gedemonstreer, en het gewys dat versteuring van natuurlike ekosisteme nie ’n voorvereiste vir S. molle indringing was nie, hoewel menslike aktiwiteite soos boomaanplantings ’n groot rol speel deur by te dra tot indringing van hierdie spesie in Suid-Afrika. Voorspelling van toekomstige verspreiding van indringerspesies is baie belangrik vir die bestuur en bewaring van natuurlike ekosisteme, sowel as vir ontwikkeling van wetgewing. Daarom is die huidige en potensiele toekomstige ruimtelike verspreiding van S. molle in Suid-Afrika bereken deur inkorporering van bioklimaatsmodelle en simulering gebasseer op ’n verspreidingsmodel. Ek het derhalwe akkurate profiele van omgewingstoestande (beide fisiese en daardie wat verband hou met menslike aktiwiteite) wat die aangeplante en natuurlike omvang van die spesie in Suid-Afrika kenmerk geproduseer deur spesiedeterminante, potensieële geskiktheid van habitatte en moontlike verspeidingsdinamika onder verskillende bestuursscenarios en kimaatsverandering te koppel. Al hierdie komponente verskaf insig in die dinamika van die indringing van houtagtige plante met vlesige vrugte oor die algemeen en S. molle in besonder in Suid- Afrika. Hierdie werk beklemtoon ook die behoefte vir hersiening van beleidsrigtings wat betrekking het op die indringerstatus van S. molle in Suid-Afrika en maak aanbevelings vir toekomstige navorsing.