The species Neuranethes spodopterodes is a pest of the Agapanthus species. The larva feeds gregariously on the leaves and rhizomes and cause extensive damage to the plant. This study shows the N.spodopterodes have 6 larval instars. The use of the head capsule width as a morphometric parameter and applying it to Dyar's rule gives significant results which allow for adequate determination of the larval instar. The Agapanthus borer has a life cycle that last approximately 84 days. Some species of Agapanthus are the preferred host plant for oviposition by the female N.spodopterodes. Agapanthus inapertus, Agapanthus caulescens and Agapanthus praecox are the most infested with the Agapanthus borer eggs. Leaf sizes do not appear to be a factor that influences the female choice. There appears to be no preference from the larva during feeding. The larva fed equally on all the six Agapanthus species including A. africanus (p>0.05). This shows that the chemical composition of these species is closely related. Since the larva has no feeding preference, this reinforces the fact that it is the female moth that chooses the host plant and that it abides with preference-performance hypothesis. Since A. africanus is subjected to feeding by the larva under laboratory conditions, it could potential imply that in the event of a range shift by the gravid female, that this species of plant is at risk of extinction. The presence of a parasitoid wasp, Trichogramma in the egg of N. spodopterodes and that the level of parasitism is about 86% suggests that this parasitoid could potentially be used as a biological control agent of the Agapanthus borer.

This thesis describes the combined toxicity in aqueous solutions of three common metals (Al, Cu and Mn) on the endemic freshwater amphipod Paramelita nigroculos (Barnard) from the south-western Cape region of South Africa. The aims of the work were three-fold: to examine the toxic effects of combinations of the three metals; to investigate such effects on an indigenous aquatic organism; and, to investigate eh adequacy of the South African "Guidelines for aquatic ecosystems", which are derived from the data based on the effects of individual elements.

No description available.

Includes abstract. / Includes bibliographical references. / Stable isotopes (SI) have been widely applied in ecology to investigate the trophic relationships of animals. Stable isotope analyses were used to augment our understanding of the foraging ecology and movements of three globally threatened seabirds: African Penguins (Spheniscus demersus), Cape Gannets (Morus capensis) and White-chinned Petrels (Procellaria aequinoctiallis). The diets of captive penguins were varied to estimate the 15N turnover rates and discrimination factors of toenails and blood fractions. Plasma δ15N showed a faster turnover rate (7.6 ± 0.7 days) than erythrocytes (14.3 ± 1.6 days). Discrimination factors varied among tissues. No shift in nail δ15N signature was detected after 5 months, suggesting that toenails are insensitive to short to medium-term diet shifts. Among wild penguins and gannets sampled across the Benguela region, tow different responses to the effects of fisheries were observed,due to different feeding strategies, Age, sex year and colony location accounted for isotopic variation. Age-based differences may be linked to limited foraging skills of juvenile birds and their wider dispersion. Female gannets apparently feed on more live natural prey whereas males take more fishery discards, although the sex-based difference was confounded by colony effect. Marked inter-colony variation probably results from regional differences in oceanic conditions between, prey availability and among gannets, variation in dependence on fishery discards. Inter-annual variation in SI signatures might be linked to variation in primary production (African Penguins), or variation in prey availability (Cape Gannets)...

Includes bibliographical references (leaves 264-279). / Eutrophication of water supplies has necessitated the development of methods to prevent discharge of excessive quantities of nitrogen and phosphorus. Operation of a generally applicable process for removing these elements from sewage effluents has not yet been reported. The investigations described here were carried out to determine the feasibility of using the nutritional requirements of controlled ecological systems for this purpose. The results are presented as an alternative approach to the chemical methods that have received consideration.

Bibliography: leaves 118-135. / This thesis addresses the population genetic consequences of divergent social structure and dispersal regimes in two study populations of the common mole-rat Cryptomys hottentotus hottentotus. Aspects relating to the relationship between, gene flow and genetic variation, the roles of mutation and drift in promoting genetic structuring, and the role of genetic parentage in the species' mating system were investigated using a suite of cryptomys-specific microsatellite markers. C. h. hottentotus is a social species living in colonies of 2-14 individuals, permanently inhabiting a network of burrows. The species is a co-operative whose colonies are composed of a breeding pair, their offspring and a number of potentially unrelated individuals. C. h. hottentotus is an obligate outbreeder whose offspring delay dispersal and the opportunities for independent reproduction until both social and ecological conditions are favourable. The species is widely distributed across South Africa from extreme arid regions where low rainfall restricts dispersal for much of the year, to highly mesic areas where dispersal is facilitated all year round. In response to varying ecological constraints on dispersal, the species displays differential degrees of social elaboration across its range. This appears to be in response to the high energetic costs of burrowing and the low probability of locating geophyte clumps in increasingly arid environments.

Includes abstract. / Includes bibliographical references. / In this dissertation, I propose a population-level framework that integrates ecology and population genetics to rethink the mechanisms that promote divergence. To accomplish that I studied two southern African endemic Cercotrichas scrub-robins: C. coryphaeus and C. signata. Despite its phylogenetic proximity the two study species occupy the two ends of the habitat spectrum available in southern Africa: semi-arid Karoo vs. Forest.

Bibliography: leaves 249-252. / The thesis decribes the reproduction, population dynamics and production, filtration, respiration and assimilation of the black mussel Choromytilus meridionalis (Kr.) at Bailey's Cottage, False Bay, South Africa. The reproductive season and gonad development is described from monthly measurements made over a period of 4 years. Spawning usually extends from July to February and is characterised by peaks of gamete release interspersed with regeneration of the gonad. Individual fecundity varies from year to year and increases with increasing body size, representing 61-97% of production. Although large volumes of gamete material are emmitted annually, spat settlement at the study site is only successful at 4 to 6 year intervals. The population dynamics at different shore levels is described in detail.

Bibliography: leaves 153-162. / This study was undertaken to assess the status of Redwing Francolin on farmland, particularly within the montane grasslands of Mpumalanga Province, and Swainson's Spurfowl within the Springbok Flats, Northen Province. To date, there had been no scientific studies of the impacts of habitat transformation via agriculture on their population biology.

Bibliography: leaves 188-216. / The main objectives of this study were to examine, by means of beach seine netting, the composition, abundance and size structure of fish assemblages frequenting surf-zone habitats in the south-western Cape, South Africa, to investigate temporal and spatial variations in these assemblages in relation to physical environmental parameters, and to assess the importance of this habitat as a nursery and feeding ground for littoral fish. In all, 54 fish species from 29 families were recorded, with three species (Atherina breviceps, Liza richardsonii and Rhabdosargus globiceps) dominating numerically. Two separate surveys were designed to provide a comprehensive assessment of the factors influencing spatial variability in the composition abundance and community structure of the surf fish assemblages in this region. In the first, surf ichthyofaunal assemblages at 11 localities, selected to encompass as wide a range of physical parameters as possible, were sampled at monthly intervals for a period of two years. Results of this study indicated that the degree of wave exposure, the presence of emergent rock on the shore and turbidity were responsible for most of the spatial variability in abundance and community structure observed. In the second survey, samples were collected at eight localities spanning an exposure gradient from highly exposed, open ocean beaches to extremely sheltered marine sandy beaches, in order to isolate and carefully examine the influences of wave exposure on surf fish assemblages. Two important trends were evident in the abundance and community structure of teleost catches in this study. Overall abundance increased markedly as wave exposure decreased, while highest species richness and diversity, and lowest dominance were recorded at intermediate levels of exposure.