Includes bibliographies. / Macaroni Penguins (Eudyptes chrysolophus) and Rockhopper Penguins (E. chrysocome) breed sympatrically at Marion Island in the sub-Antarctic, where they account for a substantial proportion of the avian biomass breeding at the island. This thesis documents the energy requirements of the two species during their respective breeding and moulting cycles at the island. Resting metabolic rates, calculated from lowest, stable rates of oxygen consumption over 24 h, averaged 25 % greater than basal metabolic rates predicted from allometric equations. Body temperatures of the penguins and the relationships between metabolic rates and temperature were investigated over a range of -10°C to 25°C. Lower critical temperature of Rockhopper Penguins was between 0°C and 5°C, but that of Macaroni Penguins could not be clearly ascertained. Measured metabolic rates of other species of penguins are reviewed and intra- and inter-specific differences in metabolic rates are discussed. In contrast to most penguins measured, individuals maintained in zoos or held in captivity for long periods had metabolic rates lower than predicted basal levels.

Bibliography: leaves 164-172. / Nectarivores feed on aqueous sugar solutions, and their water balance is tightly linked to their energy balance. When nectar is dilute and energy demands are high, consumption of a large excess of preformed water is inevitable. Physiological implications of nectarivory for the lesser double-collared sunbird, Nectarinia chalybea, have been investigated here. Sunbirds consumed 2.7 times their body mass (8 g) per day when feeding on 0.4 M sucrose at an ambient temperature of 10°C, and excreted 87 % of the water. When feeding on 1.2 M sucrose at 30°C, sunbirds drank only 0.5 times their body mass of water daily. In view of the sometimes high flux of water, combined with the low electrolyte concentrations of nectar, sunbirds must be efficient at conserving ions to maintainelectrolyte balance. When 15 mM each of KCl and NaCI were included in a diet of 0.4 M sucrose, sunbirds precisely maintained electrolyte balance by increasing cation excretion from 2 to 17 mM. Considering the high preformed water content of dilute nectar, sunbirds may expend large amounts of energy warming their food to body temperature, which was measured as 42°C irrespective of diet. Modelling revealed that sunbirds feeding on dilute (0.4 M) sucrose at 18°C would use the same proportion of their daily energy intake (4 %) to warm their food as high-latitude aquatic endotherms feeding on fish or invertebrates just above freezing point. The evaporative water loss (and therefore evaporative heat loss) of N. chalybea increased as dietary sucrose concentration decreased (more than two-fold between 1.2 and 0.2 M).

Includes bibliographical references. / This thesis examines spatial and temporal patterns in periphyton community composition and biomass and the environmental factors responsible for shaping these communities in south-western Cape rivers. The study focused on two prennial foothill rivers in the south-western Cape: the Berg River, which is oligotrophic but has a large dam (The Berg Dam) situated in its upper reaches; and the Molenaars River, which has a natural flow regime but is moderately enriched by trout farm effluent. Two site on the Berg River (one upstream and one downstream of the Berg Dam) and two on the Molenaars River (one upstream and one downstream of the Du Toit's Kloof trout farm) were used to study temporal dynamics in periphyton communities over a 21-month period between September 2007 and May 2009.

Bibliography: pages 259-272. / The tolerance of marine fish larvae to NH₃, NO₂⁻, NO₃⁻, H⁺, OH⁻, O₂, and CO₂ was investigated using the decrease in first-feeding incidence following a 24-h exposure as the criterion of response. Ten species, all hatched from pelagic eggs collected at sea, were used in the studies: two soleids (Heteromycteris, Synaptura), a cynoglossid (Trulla), a gadid (Gaidropsarus), a congiopodid (Congiopodus), four sparids (Diplodus, Lithognathus, Pachymetopon, and an unidentified species), and a centracanthid (Pterosmaris). Concentrations that inhibited first-feeding are compared to 24-h LC 50's for the same species, and to concentrations that are known to induce lethal and sublethal responses in other teleost species. Judging from their effect on first-feeding, un-ionized ammonia, elevated pH, and reduced oxygen concentration are considered to be potential hazards in the rearing tank. NO₂⁻, NO₃⁻, H⁺, and free CO₂ are nontoxic at levels likely to be encountered in practical fish culture. There are only minor inter-specific differences in calculated 24-h first-feeding EC 50's (concentration that reduces first-feeding incidence by 50%), which suggests general applicability of the results to a wide variety of first-feeding marine fish larvae. Data are presented on the age at first-feeding and point-of-no-return. The suitability of assorted micro-particles (including the rotifer, Proales, and Pine pollen) as experimental foods is discussed.

Includes bibliographical references. / The African Black Oystercatcher is currently classified as Near-threatened by virtue of the fact that the population size is small «10 000) and numbers have decreased or were previously recorded as decreasing. Aspects considered to be of conservation concern to the species are (a) its inherently low and variable breeding success; (b) its ground-nesting habit, making it vulnerable to numerous direct and indirect impacts of human disturbance; (c) its susceptibility to mass mortalities, particularly of adult birds in high-density breeding populations. Inherent factors which may of benefit to the species' persistence are its considerable longevity and, potentially, a degree of connectivity between local populations, although current evidence suggests that this is very low. However, in addition to these considerations, over the past 25+ years the variety and intensity of potential threats and benefits to the species have also changed and this may have changed the species' conservation status. While human activity has increased in many areas of the species' breeding range, African Black Oystercatcher populations may be benefiting from and increase in the number of Marine Protected Areas as well as an improved food supply in the form of an invasive alien mussel species, Mytilus galloprovincialis. In light of the key factors outlined above and the territorial nature of the species, all of which are considered to be of importance to the species' population dynamics and conservation, the main aims of this study were to: (a) reassess the global population and, where changes have occurred, to provide an explanation for these changes; (b) assess the importance of, and manner in which human disturbance may impact breeding populations; (c) assess levels of natal site philopatry and adult site fidelity in local populations; (d) assess the long-term population viability of the species; and (e) assess the potential importance of territorial behaviour in governing the population dynamics of local oystercatcher populations.

Includes bibliographical references (p. 177-194) / Hypotheses regarding the spawning strategy and recruitment of sardine (Sardinops sagax) in the southern Benguela ecosystem are tested using an individual-based Lagrangian particle tracking model linked with a 3-D hydrodynamic model of the region. Experiments focus on the dispersion of eggs and larvae among possible spawning and nursery areas. The two main areas of interest were the west coast upwelling region and the south coast shelf region (Agulhas Bank). A stage-based temperature-dependent development model is incorporated and vertical positioning schemes are tested. The spatial distribution and size structure of the sardine spawning stock for the period 1991-1999 are presented and a simple size-based fecundity model, combined with modelled recruitment, is used to determine the relative importance of each spawning and nursery area. The area of spawning plays a fundamental role in determining the destination of spawned eggs, and recruitment of sardine in the southern Benguela ecosystem appears to be divided into three recruitment systems by the circulation of the region: eggs spawned west of Cape Agulhas recruiting on the west coast (the WAB/WC-WC system), eggs spawned east of Cape Agulhas recruiting on the west coast (the CAB-WC system), and eggs spawned east of Cape Agulhas recruiting to the south coast (the SC-SC system). There is a slight increase in retention in the two nursery areas during winter, but the transport of eggs and larvae from the Agulhas Bank to the west coast is optimal during spring to early summer. Slow development arising from cold temperatures on the west coast could negatively impact recruitment by increasing offshore loss of individuals before they develop to a stage when they are able to actively avoid offshore currents and through its effect on mortality rate. This could explain the spatial separation of spawning and nursery areas in this system. The vertical position of individuals has an effect on the level of modelled recruitment and mortality rate, but observed vertical distributions of sardine egg and larvae do not significantly increase the level of modelled recruitment to optimal nursery areas. This suggests that efficient transport and retention are traded-off against other factors such as predator avoidance or prey abundance. Observed size structure and spatial distribution of the sardine spawning stock for 1991-1999 fluctuated greatly with most spawning centred on the western Agulhas Bank. When spawning was centred east of Cape Agulhas, recruitment was poor. No significant relationship could be established between potential reproductive output reaching the west coast and estimated recruitment, but positive recruitment anomalies required good transport to, and retention on, the west coast. A conceptual model of the early life history of sardine is proposed in light of limitations imposed by transport and retention of individuals. Lower primary production and the possibility of higher predation on the Agulhas Bank suggest that the south coast supports less recruitment than the west coast. The hypotheses tested using available data and model results could improve the understanding of recruitment of sardine in this complex ecosystem. These need to be validated by field observations. Additionally, further avenues for research that could help in developing a better understanding of the sardine life history in the southern Benguela ecosystem are suggested.

Bibliography: leaves 358-363. / The following aspects of physiological adaptation and resource usage were examined in several species of arid-adapted African rodents: The effect of temperature on thermoregulation, metabolism, evaporative water loss and thermal conductance was studied in the North East African pigmy gerbil, gerbillus ppusillus; This gerbil did not strictly maintain homoeothermy and like most arid-adapted rodents had a reduced basal metabolic rate. When G. pusillus was maintained on an ad lib. food and water diet, its daily energy expenditure was similar to that predicted by mass. This increased to 116% of the expected allometric value when deprived of water. On a diet of air-dried millet seeds, increased kidney concentrating ability, reduced pulmocutaneous evaporation and a reduction in faecal water loss, were sufficient to impart virtual independence of exogenous water and the maintenance of a positive water balance. If food was restricted, G. pusillus utilized torpor to precisely balance energy expenditure with that available and so maintained a constant body mass. During torpor, assimilation efficiency was significantly reduced. The cost of maintaining coenothermia for the full duration of food processing would be prohibitive and it was estimated that it would have utilised approximately 50% of the daily energy available. The cost of employing torpor (0.5kJ.day-1) on the other hand was insignificant in comparison with the savings accrued by the use of torpor (32.25kJ. day -1). Parsimony of water loss with food restriction enabled the maintenance of a positive water balance during this period. The importance of micro-habitat in thermoregulation was investigated in Gerbillurus paeba, inhabiting the thermally stable confines of a plugged burrow, and in Aethomys namaquensis, a crevice dwelling rock rat. The rock rat, living in an environment characterized by large diet ranges, precisely controlled body temperature. It did this by compensating for its reduced basal metabolic rate, with a low rate of thermal conductance. Gerbillurus paeba tolerated a labile body temperature and used a high rate of thermal conductance to remove metabolic heat, for the high humidities it encountered in its milieu would impede the use of evaporative cooling. Daily energy expenditure of both Namib rodents. Was monitored when they were maintained on a low fibre food source (golden millet) and then when this was replaced with a high fibre food source (high-bulk bran). Aethomys namaquensis showed a DEE similar to that predicted by mass and this remained constant, irrespective of the food source or the presence or absence of water. The DEE of G. paeba was more variable. When water was freely available DEE was higher than that predicted by mass and was similar to that predicted for an insectivore of similar body mass. This might reflect its propensity towards an insectivorous diet. When water-stressed on a high fibre diet, DEE of G. paeba declined by half, suggesting that G. paeba employed torpor when conditions were stressful and when the quality of resources was reduced. On a low fibre diet, both species were able to maintain a positive water balance when deprived of water, showing similar reductions in water loss to that of G. pusillus. Low assimilation efficiency and the concomitant increase in faecal water loss precluded the maintenance of a positive water balance when they were fed a high fibre food source. Despite increased urine concentrations and reduced evaporative water loss both species succumbed to chronic water-deprivation. Daily water turnovers and urine concentrating ability was monitored in 17 species of African rodents from arid areas. In general, rodents belonging to the Cricetidae exhibited lower water turnovers and voided smaller volumes of urine at significantly greater concentrations than the murids. All these cricetid rodents were found to produce a crystalline precipitate of allantoin in their urine when water stressed. The quantities of crystalline allantoin excreted were far greater than that expected from purine catabolism and accounted for 30% of the total nitrogenous wastes of the cricetids when deprived of water. It was thought that the substantial quantities of allantoin excreted were responsible for the lower water turnover rates in the cricetids. It is suggested, therefore, when water is limiting, there is a shift in the nitrogen pathway from urea to allantoin, so conferring an eco-physiological advantage to these long term residents of the arid regions of Africa.

Includes bibliographical references. / The African penguin is a southern African endemic, with its breeding distribution within the Benguela Upwelling Ecosystem. The IUCN conservation status of this species was re-classified from ‘Vulnerable’ to ‘Endangered’ in 2010. This thesis investigated some aspects pertinent to the species’ conservation and management. Time series of population estimates of African penguins and fish biomass were available in South Africa since the late 1980s. This study analysed the fish biomass at a stratum scale, which is a finer scale to that of previous studies which looked at biomass estimates as a whole. The strata range in length from c. 155 km to c. 280 km in length. The number of African penguin breeders and adult moulters were found to be positively correlated with fish biomass estimates, although results of the spatial relationships were unexpected. The islands which displayed the strongest relationships were Dassen Island and Robben Island. These islands are only c. 50 km apart, and it is expected that they would experience similar oceanographic conditions. However, the colonies at these islands were found to respond differently to fish biomass estimates. While the number of Dassen Island birds were found to be positively correlated with biomass estimates within the strata in which the island is found, the number of Robben Island birds were correlated with biomass estimates of the stratum to the south and east of the island. Weaker relationships were found for the remaining colonies. This study suggested that the period of moult is of critical importance to the survival of the penguin, an aspect that needs to be incorporated into the Ecosystem Approach to Fisheries modelling.

Includes bibliographies. / This thesis consists of five chapters. One is a published paper, two are in paper format, and one is a thesis chapter. The thesis is preceded by a general introduction. The central theme of this work is the population ecology and feeding biology of rocky-shore crabs on the Cape Peninsula. The biology of three crabs is examined, namely, the ubiquitous brown shore-crab Cyclograpsus punctatus (M.Edw), the Cape rock-crab Plagusia chabrus (De Haan) and the invasive European shore-crab Carcinus maenas (L.). The possible impact of C. maenas upon the South African intertidal and local crabs in particular is also assessed.

Bibliography : leaves 59-65. / Competition for pelagic fish resources was investigated by assessing the overlap in the food base of three land-based predators: Cape gannet (Morus capensis), Cape fur seal (Arctocephalus pusillus pusillus) and humans operating via a purse-seine fishery. Multivariate analysis the diet composition of gannets and seals and the catch composition of the pelagic fishery indicated that there were three ""feeding regimes"" during the 21-year study period: (1978-1998), an anchovy-dominated regime (1978-1983), an intermediate regime (1984-1990) and a sardine-abundant regime (1991-1998). It further showed that anchovy (Engraulis capensis) and sardine (Sardinops sagax) contributed substantially to the catches of all three top predators. Analysis of size-distributions of catches showed that the three predators generally caught the same sizes of anchovy and sardine, reflecting very little resource partitioning. The analysis demonstrated stronger competition between gannets and the purse-seiners than between gannets and seats, especially during seasons of poor recruitment. Furthermore, seasonal differences in the catches of the three predators are related to the recruitment, growth and migration of the prey species. The study confirmed previous observations that gannets prefer sardine to anchovy by showing gannet exploitation of sardine in the early 19905, when anchovy was still abundant. The gannets, which are species-specific feeders, may be impacted by substantial removals of pelagic fish resources by a large seal population and a large fishery.