Includes bibliographical references. / Introduced house mice Mus musculus on Gough Island were suspected of widespread predation of Atlantic Petrel Pterodroma incerta and Tristan Albatross Diomedia dabbenena chicks in 2000/01. Video cameras recorded six fatal attacks by mice on live, healthy Atlantic Petrel chicks in 2004. Crude estimates of annual breeding success were 47%, 7% and 7% in 2003, 2004 and 2006, respectively. Mouse attacks were responsible for most chick failures. Mice were largely responsible for high numbers of Tristan Albatross chick failures in 2004-2006. Total failures were significantly related to total attempts but breeding success and total attempts were not correlated. There was little spatio-temporal consistency in total failures or breeding success. No environmental or biological variables examined explained the pattern. Proximity to a failed nest was a significant predictor of failure, suggesting a localised effect possibly due to a few predatory mice. Fledgling production has decreased by 1% annually since 1979-1982. Annual adult Tristan Albatross survival and breeding success averages are extremely low (91% and 32%, respectively) and modelled population growth using these parameters was - 2.85% p.a. Either parameter will drive decreases so reversing negative trends requires improving both.

Bibliography: leaves 195-210. / Spatial and temporal heterogeneity of lotic systems was examined by assessing variability in macroinbertebrate assemblages in two geographic regions, the Western Cape and Mpumalanga, in South Africa. Assemblages were assessed using the South African Scoring System (SASS), a rapid bioassessment method. The implication of spatial variability at regional, subregional and habitat levels, and temporal variability for defining reference conditions for macroinvertebrates was evaluated.

Bibliography: leaf 321. / During the past decade, South Africa has experienced an unprecendented degree of industrial expansion. Although this has enhanced the material wealth and personal comfort of all the nations' peoples, it has also produced an undesirable consequence - ever increasing pollution of the aquatic environment. Viable systems for continuously monitoring water quality are, therefore, of critical importance for the future management and use of our watersheds. The value of regional monitoring programs using physical and chemical measurements is already well established. The major difficulty with this type of monitoring system, however, arises in the analysis of the data and in making evaluations of a complex ecosystem from the measurements of a few physical parameters such as dissolved oxygen, pH, temperature and conductivity. Further, it is difficult, if not impossible, to predict the biological effects of a complex continuously changing industrial effluent from chemical analyses alone.

Includes abstract. / Includes bibliographical references (p. 193-216). / The aim of this study was to incorporate all lines of evidence to establish the true taxonomy and phylogeny of southern African Zosterops. Character data sets used include plumage and morphometric measures, vocal characters and molecular (mitochondrial and nuclear) DNA sequences. A broad scale phylogeographic analysis was also performed to establish the evolutionary process driving the diversity observed among these birds.

Includes bibliographical references (p. 259-293 ). / Lagarosiphon ilicifolius Obermeyer and Vallisneria aethiopica Fenzl are the most common and abundant submerged macrophytes in shallow inshore waters of Sanyati Basin, Lake Kariba. Lagarosiphon is structurally more complex than Vallisneria. This study considered the macroinvertebrate assemblages associated with the two plant species with respect to (i) differences in structural complexity, (ii) predator-prey interactions and (iii) water physicochemical conditions.

It has been suggested that natural fires in these grasslands would have occurred as infrequently as every four or more years. Currently, the majority of the system is managed by livestock farmers who burn their land annually at the onset of the rainy season (early in the austral summer).

Includes bibliographical references. / Three abundant small pelagic fish species co-occur in the Benguela upwelling ecosystem off southern Africa: sardine (Sardinops sagax), anchovy (Engraulis encrasicolus) and round herring (Etrumeus whiteheadi). It is hypothesised that populations of these species have a complex structure that reflects the complexity of their varying habitats. On the basis of the locality and timing of spawning, and morphological, meristic and parasite studies, it has been proposed that there are separate stocks of sardine in South African waters west and east of Cape Agulhas. Consequently, new operational procedures for managing the fishery are based on the premise of two such stocks, termed the west and south coast stocks respectively. In this study, it is hypothesized that the factors causing purported stock differences in sardine should also apply to anchovy and redeye. Three different approaches were used to further test the multi-stock hypothesis for sardine in southern Africa and to provide new information for understanding possible stock differences in anchovy and round herring. The population structure of sardine was investigated through studies on samples taken from the Cape west and south coasts as well as from Namibia and KwaZulu-Natal. Two dimensionless otolith shape indices, otolith elemental signatures, seven microsatellite loci and the mitochondrial DNA marker, ND2, were used to supplement existing information on sardine. Otolith shape, while influenced by fish length and season of capture, distinguished the east coast samples from those taken elsewhere, while the otolith elemental signatures indicated differentiation among sites on a small scale and between samples taken from the west and south coast for certain elements. Both genetic indicators showed high levels of genetic diversity and variation among individuals. There were some genetic differences among sites within a single year, but overall the results suggest that the South African sardine population is well mixed, with weak evidence of genetic patchiness that is not temporally stable. This genetic pattern is evidence of sweepstake recruitment. For anchovy, two spawning locations have been identified in South African waters, but there have been no previous investigations into stock structure. The current study aimed to apply different methods to anchovy samples to determine their usefulness for differentiating population structure,. An analysis of otolith shape revealed that it was primarily influenced by the length of the fish, with no differentiation among sites, whereas an investigation into genetic differentiation using five microsatellite markers revealed high levels of genetic diversity and differentiation among sites. Since there were relatively few samples for a study of this sort, further work is recommended to investigate stock structure in South African anchovy. For round herring, only otolith shape was analysed to test for stock structure. Otolith shape was found to be primarily related to the length of the fish (as in anchovy) and sex, but no significant difference was found between coasts. There were different magnitudes of variability in the results for the three species using different methods. It is likely that the complex, variable environment causes complex patterns of mixing and micro-structuring within all three species, linked to their different niches.

Bibliography: pages 181-205. / In the southern Benguela upwelling system, anchovy spawn serially between September and February each year. It has been suggested that this energy-intensive reproductive strategy requires continual ingestion of copepods, which dominate the diet of anchovy at this time. This thesis investigates the spatial and temporal variability of copepod abundance and growth, and their impact upon the spawning of anchovy. Sampling was conducted monthly between August-March 1993/94 and 1994/95 .. It is noteworthy that the primary spawning ground of anchovy, the western Agulhas Bank, had a significantly smaller biomass of copepods than the adjacent West Coast region. In terms of the growth rates of copepods, the effect of food-limitation on fecundity and somatic growth outweighed that of temperature.

This thesis is concerned with the contrasting communities that occur in the subtidal zones of two closely situated islands in Saldanha Bay on the west coast of South Africa: Both are guano islands, supporting substantial populations of seabirds. They have a similar bottom topography and experience similar physical conditions. Despite these similarities their subtidal benthic communities are however, radically different. Marcus Island has prolific beds of the black mussel Choromytilus meridionalis, accompanied by a large number of other species, notably the sea urchin Parechinus angulosus, the holothurians Pentacta doliolum, Thyone aurea and Trachythyone insolens, large population of whelks, mostly Burnupena spp. and the barnacles Austromegabalanus cylindricus and Notomegabalanus algicola. In contrast, Malgas Island is dominated by a large population of the rock lobster Jasus lalandii together with a dense seaweed flora, and has small numbers of the ribbed mussel Aulacomya ater and the whelks Argobuccinum pustulosum and Burnupena papyracea.

Includes bibliographial references (leaves 222-234). / Thirty-six species of ants were collected in the central Namib Desert, Namibia during the period 1981 to 1985. The ant fauna was dominated by the Myrmicinae, comprising 29 species, followed by the Formicinae, comprising six species and the Pseudomyrmecinae with one species. The dominance of the ant fauna by these subfamilies was in part attributed to the abilities of certain members of these ant groups to store food. The majority of ant species occurred on the gravel plains where species richness was strongly correlated with mean annual rainfall, an index of primary productivity. Certain species were strongly associated with perennial vegetation reflecting the ants' requirements for honeydew, nectar and/or nesting sites. The vast majority of ant species were not dependent on perennial vegetation and relied primarily on seeds, insects or both for food.