Bibliography: leaves 88-97. / Annual macrofaunal and meiofaunal standing stocks were estimated on an exposed rocky shore along the west coast of False Bay, South Africa, using comparable area based sampling techniques. While meiofaunal densities exceeded those of macrofauna in all zones, by an overall ratio of approximately 400:1, macrofaunal biomass exceeded that of meiofauna by an overall ratio of 10:1. The numbers of meiofauna were not evenly distributed across the shore but varied with the algal standing stocks in each zone and their sediment load. By incorporating turnover ratios from the literature, mean annual productivity ratios were calculated which suggested that meiofauna were responsible for 25 of total (excluding bacterial) secondary production. To follow this up, the impact of wave exposure on the meiofauna of one species of alga (viz. Gelidium pristoides) was examined on five shores around False Bay. Meiofaunal densities (dominated by animals between 63um-280um) were significantly greater on sheltered than exposed shores. As the minimum width of Gelidium fronds exceeds that of these permanent meiofauna, and tufts offer little resistance to wave action, only those individuals living in the dense, holdfast region of plants could escape the impact of waves on exposed shores. Total meiofaunal biomass per plant remained constant irrespective of shore type, due to the greater numbers of juvenile bivalves and amphipods on exposed shores. Algal and herbivore biomass were not significantly different between shore types around False Bay and therefore, the proportional contribution by meiofauna to total secondary production on sheltered shores was predicted to be greater than on exposed shores, where the biomass of macrofaunal filter feeders was very high. It has previously been argued that differences in meiofaunal communities between plant species are a result of differential surface area, number of habitats and refugia from predation. The possible fate of meiofaunal productivity as food for higher trophic levels (fish) and the mediating role played by algal complexity was investigated in a series of carefully designed laboratory and field experiments.

Includes bibliographies. / This thesis presents the findings of a two-year (1986-1988) study of a mountain stream draining a small catchment in the south-western Cape, South Africa. The catchment was deliberately burnt half-way through the study period. The study was undertaken because although fire is a major natural disturbance, and also a major tool in the management of mountain catchments in the region, the effects of fire on stream ecosystems was entirely unknown.

Bibliography : leaves 134-152. / The Helmeted Guineafowl Numida meleagris is, naturally, a species of open savannas. However, since the mid-18th century, it has undergone the most extensive range expansion of any African gamebird. In southern Africa, this expansion has been mostly due to a combination of deliberate introductions and the natural expansion into areas transformed by agriculture and urban development, which supply key resources such as food, cover, roosting sites and watering points. The Midlands of KwaZulu-Natal province have been no exception in this regard. With the advent of, in particular, crop agriculture, large populations of guineafowl have occupied, and increased numerically in, this variegated landscape since the turn of the 20th century .

Includes bibliographies. / Three species of southern African mole-rats, possessing a wide range of social organisation were used to investigate the trend towards increasing sociality occurring in species inhabiting increasingly arid environments. The strictly solitary Georychus capensis, the weakly social Cryptomys hottentotus hottentotus and the highly social Cryptomys damarensis were chosen for this investigation and my findings are compared, where possible, with the eusocial Heterocephalus glaber. The level of social organisation exhibited by a particular mole-rat species appears to be dependent upon a number of physical factors as well as on the food resource distribution, its nutritional properties and its availability. Thus the soil moisture content, the annual rainfall pattern and the wear upon the extrabuccal incisors limit the amount of burrowing which can be undertaken by a single mole-rat, both on a daily and seasonal basis. These factors together with the size, distribution, digestible energy and fibre content of the geophytes on which they feed and nearest-neighbour distances occurring between the belowground portions of the geophytes, may be crucial in determining whether a habitat is suitable for solitary or colonial mole-rats.

Bibliography: leaves 148-160. / The effects on birds of fine-scale differences in plant species assemblage and vegetation structure, and of two major disturbance factors (woody alien plant infestation and fire), were investigated in Mountain Fynbos at two sites in the southwestern Cape Province, South Africa. Three associated processes were also studied. These were the relative importance of three animal taxa as seed predators following fire, the extent to which an indigenous bird species ate alien Acacia cyclops fruits, and potentially dispersed its seeds, and the number of nectarivorous birds which visited an isolated nectar resource. Avian responses to fire in Mountain Fynbos varied according to season, locality and burning regime. Recently and cleanly burnt fynbos at a flat, low altitude, coastal site supported a distinctly non-fynbos avifauna, characterized by relatively large-bodied, ground-feeding, opportunistic species.

Includes bibliographical references (leaves 69-86). / In South Africa, both wild and cultivated oysters are consumed. Edible wild oysters include Striostrea margaritacea, Saccostrea cucullata, Ostrea atherstonei and 0. algoensis and all occur along the South and East coasts. These oysters were, or are, exploited commercially, recreationally and via subsistence fishers with S. margaritacea being the most targeted species. The commercial harvesting areas are along the Southern Cape coast and in KwaZulu-Natal. The Southern Cape coast is the largest harvesting area with 102 of the 145 pickers employed in the region. Commercial and recreational harvesting is managed by the Marine and Coastal Management Branch of the Department of Environmental Affairs and Tourism. Data on the total annual catch of oysters in these provinces are minimum estimates, as collectors do not always comply with the harvesting regulations. Subsistence harvesting is largely unmanaged, except in KZN, and is particularly rife in the Eastern Cape Province. The culture of oysters is dependent on importing Crassostrea gigas spat mostly from Chile. Oyster production statistics are only available since 1985, but approximately two million Crassostrea gigas oysters were produced annually throughout the seventies and early eighties. Since then, production has fluctuated over the years with an approximate increase of six million between 1985 and 1991, a decrease of five million between 1991 and 1998, and is presently stable. The establishment and closure of a highly productive farm in the late eighties and early nineties respectively, as well as improved production in recent years, has resulted in these trends. Although the market for oysters has grown, production has not kept up with demand, due to a lack of suitable locations for mariculture purposes. Finding suitable sites for oyster cultivation along the Northern Cape coast and establishing local oyster hatcheries for C. gigas oysters is suggested as the way forward. The latter would also prevent associated marine alien species from being imported with spat. Globally, oysters are well known vectors of marine alien species and despite oyster imports as early as 1894 into South Africa, this topic has been afforded little or no local attention. A visit to various oyster farms in South Africa resulted in the discovery of four newly-recorded alien species: the black sea urchin Tetrapygus niger, from Chile, the European flat oyster Ostrea edulis, thought to be locally extinct following its intentional introduction into South Africa in 1946, Montagu's crab Xantho incisus, from Europe, and the brachiopod Discinisca tenuis, from neighbouring Namibia. Oyster imports are suggested as their most likely vector into South Africa and the biological attributes of some emphasizes the possible threat and the need to limit or prevent their spread. Local or intraregional translocation of C. gigas and associated species, including aliens colonizing the area, may aid in this spread. Oysters host a diverse community of epi-and infaunal fouling taxa, which can be accidentally translocated along with their hosts in the course of commercial oyster trade. Thus, the types and quantities of fouling taxa occurring on farmed Crassostrea gigas were examined. How effectively these taxa are removed by standard cleansing techniques and whether those that persist after washing, survived intraregional translocation, were also examined. Cleaning and translocating oysters significantly reduced both the quantity (by more than 30 and 40 times respectively) and variety of fouling taxa. Although the mean abundance (A) or biomass (B) of taxa in uncleansed oysters (A: 79.48±233.10 (SD), B: 0.034±0.314 (SD)) were greatly reduced in cleansed oysters (A: 2.30±7.65 (SD), B: 0.0003±0.002 (SD)), small quantities still managed to survive translocation (A: 1.87± 7.43 (SD), B: 0.006±0.020 (SD)). Thus, the effectiveness of exposing oysters to freshwater or heated seawater as a more thorough cleansing regimen, to prevent the translocation of such taxa, were examined. Results indicated that oysters were able to survive for a longer time in freshwater (0% mortalities after 18 h) than in heated seawater (26.7% mortalities after 40 sec), but most taxa were eliminated more effectively by the latter treatment (e.g. 88.5% of the mudworm Polydora hoplura died after 20 sec compared to 97.5% after 18 h in freshwater). However, only a single reproductive individual of an alien species may be required for a successful introduction, and soaking for 20 sec in heated seawater would still be ineffective. An alternative treatment of 18 h in freshwater and 20 sec in heated seawater or freshwater, is suggested as a more effective treatment.

Includes bibliographical references (leaves 37-42). / Sea ice covers vast regions of the Southern Ocean and impacts on the climate as well as the plant and animal life of the region. The variability of sea ice in the Southern Ocean affects the entire food web of the region, from phytoplankton to Antarctic krill through to the apex predators such as seals and penguins. Sea ice variability is determined by shifts in the atmospheric temperature distribution and shifts in the atmospheric circulation. The Southern Annular Mode (SAM) is the primary mode of variability in the atmospheric circulation of the Southern Hemisphere. Despite the overall warming of Antarctica, sea ice extent and sea ice area show a positive trend in the Southern Ocean and all its sectors except in the Bellingshausen/Amundsen Seas sector which displays a negative trend for the period 1979-2007. The SAM index also shows a positive trend during this period indicating a shift towards the more positive phase. The monthly and seasonal correlations between the SAM index and sea ice concentrations display a dipole, with more ice occurring in the Ross Sea during the positive phase of SAM and less ice occurring in the Weddell Sea.

Bibliography: leaves 151-176. / A long term behavioural study was undertaken on laboratory-reared naked mole-rats. The main objective of the study was to provide a detailed qualitative and quantitative description of the behavioural and morphological development of naked mole-rats from birth through to adulthood. This study laid an empirical foundation for the subsequent testing of hypotheses pertaining to within and between colony conflict as well as for a study on the existence of a rare dispersal phenotype within colonies.

This research project investigated the impact of predation by the Cape fur seals Arctocephalus pusillus pusillus on the conservation status of seabirds at islands off the coast of South Africa and at the Prince Edward Islands. At Malgas Island, the impact of predation was investigated over three breeding seasons (2000/01, 2003/04 and 2005/06), and at Dyer Island over two breeding season (2004 and 2006/07). At Marion Island (Prince Edwards Islands) and at other South African islands, such as Dassen Island, Bird Island at Lambertâs Bay and Robben Island, observations were collected opportunistically. Cape fur seals were estimated to have killed some 6 000 Cape gannet Morus capensis fledglings around Malgas Island in the 2000/01 breeding season, 11 000 in 2003/04 and 10 000 in 2005/06. This amounted to an estimated 29%, 83% and 57% of the overall production of fledglings at the island in these breeding seasons respectively. Preliminary modelling suggests this predation is not sustainable. There was a 25% reduction in the size of the colony, the second largest of only six extant Cape gannet colonies, between 2001/02 and 2005/06. At Dyer Island, it was estimated that seals killed up to 7% of African penguin Spheniscus demersus adults annually. The present mortality attributable to seals is considered unsustainable. Seals also killed a substantial proportion, 4â8%, of Cape cormorant Phalacrocorax capensis fledglings as they left the island. Although this level of mortality may be sustainable for Cape cormorants, this species have also been affected by disease. iv Predation on seabirds by Cape fur seals was demonstrated to occur at several other localities in southern Africa but observations were insufficient to enable the effect of such predation to be quantified. Several hundred Cape gannet fledglings were killed annually at Bird Island (Lambertâs Bay) and threatened penguins and cormorants were attacked at other localities. At subantarctic Marion Island, Antarctic fur seals A. gazella fed on king Aptenodytes patagonicus and macaroni Eudyptes chrysolophus penguins. However, predation there on seabirds by subantarctic fur seals A. tropicalis has not yet been observed. King penguins were mostly killed in winter and macaroni penguins (which are absent from the island in winter) in summer. Predation of seabirds by seals has recently increased in southern Africa and may be doing so at Marion Island. In both regions fur seal populations are expanding. The influences of environmental factors on the rate of predation were investigated at both Malgas and Dyer Islands. Of environmental factors considered, time of the day had the most important influence on predation by Cape fur seals on fledglings of Cape gannets and Cape cormorants and adult African penguins. Fledglings of gannets and cormorants were mainly killed between mid morning and late afternoon, coinciding with the time they left the islands and were in the water. Most adult African penguins were killed as they returned in the evening from foraging at sea. Wind speed and direction, sea state and tide had a variable and lesser influence on predation rates. Although these variables might be used to interpolate predation rates through periods when observations are not conducted, their contribution is limited and there will remain considerable uncertainty in the estimate of actual numbers of fledglings killed. Uncertainty will best be decreased by extending the period of observations so as to reduce the amount of days for which predation rates are interpolated. v In six years between 1999 and 2008, 141 Cape fur seals that were feeding on, or thought to be feeding on, Cape gannet fledglings as they left Malgas Island, South Africa, were shot and collected. Examination of the stomachs of 93 of these seals showed that Cape gannets contributed an average of 70% by mass to the diet, and known prey items of Cape gannets, which may have been obtained from the alimentary tract of the fledglings, a further 5%. Hence, when the seals were culled, they were subsisting mainly on the fledglings. Other prey items of the seals included rock lobster Jasus lalandii and common octopus Octopus vulgaris. All the collected seals were bulls. Their ages were estimated from measures of their total length and previously published information on ages at length. All were 10 years old or less, and their mean age was 4.5 years. The hunting behaviour of Cape fur seals feeding on seabirds at Malgas and Dyer Islands was investigated in 2003/04 and 2005/06; and 2004 and 2006/07 respectively. At these islands, attacks on seabirds were identified mainly through the presence of other birds overhead and sometimes by the thrashing of a victim in, or throwing of it from, the water. Most attacks occurred beyond the surf zone at distances of 20â100 m from the island. Seals hunted in groups or solitarily and usually attacked birds from underneath or behind. Usually most, or a substantial portion of the carcass was utilized but some surplus killing was observed. On average, attacks lasted 11 min for both Cape gannets and Cape cormorants and 16 min for African penguins. Due to the increase in seal predation, interventive management such as culling individual fur seals seen preying on seabirds was implemented at Malgas Island. It was anticipated that removal of the small number of individual seals which target seabirds would reduce vi mortality on the seabirds because this is a learned behaviour. In the 2006â07 breeding season of Cape gannets at Malgas Island, the removal of 61 Cape fur seals that preyed on gannet fledglings when they left to sea significantly reduced the mortality rate of these fledglings in the short term. However, because seals learned to avoid the boat used for their removal, it was not possible to remove all the seals that killed gannet fledglings and some mortality continued. There was a decrease over time in both the maximum and the mean age of seals culled. Sustained removal of these animals may reduce this feeding behaviour.

Weeds are responsible for about 30 percent of all crop losses worldwide, but all weed research, including biological control, receives only about 10% of crop pest control support. The impact of weeds is insidious, diffuse, and complex Increased use of biological control may help to reduce the massive quantity of energy and time now expended for weed control worldwide. Batra (1981) "The vitality of biocontrol of weeds requires two types of evaluation before a project is completed. To maintain financial support it is necessary to show that biocontrol is an economical method of solving certain types of weed problems and to improve the effectiveness of biocontrol in the future, it is necessary to have scientific feed-back. Essentially, the first type of evaluation is concerned with what has been achieved and the second with why the result, either success or failure, has been achieved." Harris (1980a) The biological control of weeds using insects is a young science. The first intentional use of an insect to control a weed was in 1863 in India where the cochineal insect, Dactylopius ceylonicus (Green), was dispersed to control Opuntia vulgaris Miller some 68 years after the accidental introduction of this insect to that country (Goeden, 1978; Moran & Zimmermann, 1984). However, the first full scale attempt at a classical weed biocontrol programme was against Lantana camara L. in Hawaii in 1902 (Goeden, 1978; Harley, 1985a). By 1984 there had been 499 releases of exotic invertebrates and fungi, 488 of which were insects, for the control of 101 weed species in 70 countries (Julien et al., 1984). Despite this marked increase in the number of biocontrol programmes in later years, attempts which failed have rarely been studied or documented and even successes are seldom adequately quantified. This has been implied by Harley (1985a), Julien, (1982), Julien et al. (1984) and Maw (1984). The pressure to produce results and the difficulty of determining the reasons for failures are prohibitive (Dennill et al., 1987; Appendix 6; Goeden & Louda, 1976). The advancement of this science thus relies heavily on the study of its successes. This thesis is an evaluation of the gall wasp Trichilogaster acaciaelongifoliae as a biocontrol agent for the weed Acacia longifolia in South Africa. The wasp has been successful, and, in accordance with Harris (1980a), my aims were twofold: to quantify that success and to provide reasons for it. This information not only produces guidelines ii for the future selection of biocontrol agents, sensu Harris (1980a), but also serves as a means of enhancing our understanding of insect-plant relationships. In addition, this thesis provides an indication of the potential of gall forming insects in biological control of weeds. Gall formers have seldom been used to control weeds (Julien, 1982; Maw, 1984). Since their effects are indirect compared with those of insects attacking vegetative plant parts, their potential for weed biocontrol has apparently been underestimated in the past by some authors (Goeden, 1983; Harris, 1973; Hokkanen, 1985a). The present attempt is the first ever in which a gall forming hymenopteran has been used to control a weed, and shows beyond doubt that certain gall formers can have strong potential in this field. Chapter 1 concerns the establishment of the wasp, its population increases, dispersal, host-seeking, and the reduction of reproductive potential of A. longifolia populations. The development of new techniques that were necessary for the determination of these parameters is included. Emphasis is placed on the reasons for the successful establishment and rapid population increases observed. The potential of the insect for suppressing both reproduction and growth of the weed is great, and is examined in detail in Chapter 2. The phenological information obtained during the course of this study showed important inadequacies in the knowledge of the phenology of A. longifolia. This is rectified in Chapter 3 in which the implications of an incomplete understanding of weed phenology for biological control are emphasised. In particular, the resource allocation between reproduction and growth of the plant provides a crucial setting for the next chapter. In Chapter 4 the nature of the galling by T. acaciaelongifoliae and its relation to the phenology of A. longifolia are examined in order to explain how the wasp is able to exploit its host so effectively under South African conditions. Chapter 5 deals with the release of the wasp throughout the South African range of the weed and the identification of regions in which its performance appears inadequate. The climates of South Africa and Australia are compared to determine to what degree the establishment of T. acaciaelongifoliae in various regions in South Africa is related to the climate of the regions in which the wasp was collected in Australia. This chapter includes maps illustrating weed distribution, co-ordinates for all release points, and documents the method whereby the wasps were released. Chapter 6 is an essay dealing with the implications of the study, both practical and theoretical. Recommendations regarding the future selection of biocontrol agents are made, with emphasis on perspectives emerging from this thesis, and the future role of the wasp in the control of A. longifolia in South Africa is discussed.