Includes abstract. / Includes bibliographical references (leaves 75-93). / Miniature temperature-sensitive data loggers were implanted into the abdominal cavities of 16 free-ranging Cape ground squirrels, Xerus inauris, to investigate seasonal body temperature patterns. Data loggers recorded body temperature at 5-min intervals while microclimate variables were recorded in situ at 15 minute intervals. The behaviour of the study animals was recorded using 5-min scan samples throughout the day. These data were collected for eight Cape ground squirrels for 27 and 28 days during the austral winter and summer respectively.

Bibliography: p. 242-264. / The X-organ sinus gland complex, situated in the eyestalks of decapod crustaceans, are known to be a source of a variety of neuropeptide hormones that regulate a number of diverse physiological processes. This neuroendocrine complex was investigated in 3 crustacean species, viz. the European shore crab Carcinus maellas, and 2 spiny lobster species Jasus lalandii and Panulirus homarus by means of tissue immunocytochemistry and an enzyme-linked immunosorbent assay (ELISA). Positive immunoreactions, associated with the X-organ - sinus gland system only, were obtained with antisera raised against crustacean hyperglycaemic hormone (cHH) of the American lobster (Homarus americanus), the Mexican crayfish (Procambarus bouvieri) and the edible crab (Cancer pagurus), as well as with antisera raised against vitellogenesis-inhibiting hormone (VIH) of the H. americanus and moult-inhibiting hormone (MIH) of C. pagurus. This is the first time that the immunolocalisation of these 3 hormones have been studied in a single crustacean species. The chief results of this comparative immunocytochemical study showed that (1) neuropeptide hormones of the shore crab and the 2 spiny lobster species were sufficiently homologous in primary structure to be recognised by the heterologous antisera, thus, an indication of conserved peptide structures across the species and infraorder boundaries; (2) preabsorbed complexes of purified peptides and antisera from the edible crab did not produce any immunoreactions in tissue immunocytochemistry, nor in ELISA, thus, indicating the specificity of the anti-cHH and anti-MIH sera; (3) the anti-VIH serum demonstrated the ability to bind epitopes on cHH and MIH peptides and is, thus, not a specific antiserum in this study; (4) there is co-localisation of cHH, MIH, VIH immunoreactivity in the eyestalk neuroendocrine complexes of all 3 species studied which suggests that the different peptide hormones can be synthesized in the same neuronal cell bodies. This co-localisation of neuropeptides in the eyestalk of J lalandii was confirmed by a double-staining immunoflourescence experiment, and finally (5) immunoreactivity of antisera raised against cHH of H. americanus and MIH of C. pagurus was associated with distinct and unique peak fractions, following reverse-phase high pressure liquid chromatographic (RP-HPLC) separation of sinus gland extracts from J. lalandii. A total of 6 neuropeptide hormones belonging to the cHH/MIH/VIH peptide family were isolated, functionally characterised and sequenced from extracts of sinus glands from the South African west coast rock lobster, Jasus lalandii. This is the first complete report on these peptides from any species belonging to the Palinuridae infraorder.

Bibliography: leaves 93-102. / Many southern African crop farmers regard the Eyptian Goose (Alopochen aegyptiacus) as a widespread and major agricultural pest. Cereal crop farmers on the Agulhas Plain in the Western Cape province of South Africa are concerned that populations of Egyptian Geese have increased since the early 1990s, and are causing serious damage to their crops.

Bibliography: leaves 111-128. / Standard Geographical Information Systems (GIS) techniques and Generalized Additive Models (GAM), nonparametric regressions without the assumptions of normality or linearity of traditional regression methods, were used to test the hypothesis that trends in hake (M. paradoxus and M. capensis) distribution and abundance are related to ocean environmental conditions (including bottom temperature, bottom oxygen concentration, sea surface temperature and sea surface minus bottom temperature, as a measure of stratification or mixing) and location (including longitude, latitude and bottom depth). Hake and physical data, from seventeen biomass surveys undertaken by Marine and Coastal Managment between 1984 and 1997 in the southern Benguela ecostystem, were used to test these relationships.

Bibliography: leaves 138-147. / Land management practices have been implicated as a cause for the decline of many grassland-nesting birds across the globe. While this effect has motivated extensive research and conservation in the developed northern hemisphere, it remains poorly addressed in southern hemisphere. Between 1998 and 2001 I examined the effect of fire frequency and grazing intensity on the density, breeding biology and nesting success of several grassland bird species that breed in the high altitude grasslands of Wakkerstroom, South Africa. I established study plots in heavily grazed and annually burned, lightly grazed and annually burned, and lightly grazed and biennially burned plots. These represent the most frequently used grassland management regimes in this region. Independent analysis of all study species showed that daily nesting success was higher under light than heavy grazing. Similarly, nesting success was higher under biennial burning when compared to annual burning. Nest predation was the major cause of nest failure during all three years for all species. The likelihood of nest predation clearly depended upon foliage in the immediate vicinity of the nest and vegetation within 10 m radius of the nest (the nest patch). In general, variables important in discriminating between successful and depredated nests across all species were directly related to vegetation cover, density and horizontal heterogeneity. I also examined micro-habitat choices, the form of natural selection and the adaptiveness of preferences in four coexisting grassland bird species (Yellow-breasted Pipit Hemimacronyx chloris, Grassveld Pipit Anthus cinamomerous, Orange-throated Longclaw Macrony capensis, and Ayre's Cisticola Cisticola ayressii). Breeding birds selected nest patches non-randomly and this differed between species. Comparison of vegetation features at successful and unsuccessful nests supported the idea that nesting success is a strong selective force on habitat choice. Nest success was higher in preferred than non-preferred habitat for all the four species, suggesting that preferences were adaptive. Estimation of fitness functions relating fitness of individuals to critical habitat features suggests that natural selection might favour preferences for specific habitat features. Although food abundance and thus amount of food available to populations of breeding birds significantly differed between management regimes, the study yielded no evidence for an effect of management-mediated food abundance on feeding rate, nestling provisioning rates, nestling growth rates, body condition, nest attentiveness and brooding effort. My results suggest that the food availability alone may not be the most important factor influencing the production of offspring. Instead, nest predation appeared to be of major importance in this system. Theoretically, nest predation increases with activity at nests, and predation rates should peak during the nestling stage when birds are feeding young. I tested this hypothesis using three ecologically similar grassland bird species (Yellow-breasted Pipit, Orange-throated Longclaw, and Grassveld Pipit). Parental activity was indeed greater during the nestling than incubation stage. Nest predation, however, did not increase with parental activity between these stages in all three study species. I conducted an experiment that controlled for parental activity (by reusing natural nests of the study species with artificial clutches) in order to test for nest-site effects. Nests that had a high risk of predation when used by active parents had a correspondingly high risk of predation when the same nests were re-used with artificial clutches (i.e. when controlling for parental activity). This result supports the notion that variation in nest-site quality often affects nest predation risk, and such effects could mask parental activity effects on nest predation. Once-nest site effects were accounted for, nest predation showed a positive increase with parental activity during the nestling stage within and across species. Collectively, the chapters of this thesis help to diagnose the causes and underlying mechanisms of grassland bird population decreases, and help to identify the most effective conservation actions. In short, conservation effort for grassland species should be directed at ensuring that their preferred critical nesting habitat is managed appropriately. I propose that current intensive grazing pressure and periodic burning should be relaxed by reducing stocking rates and burning less frequently to benefit grassland bird species. Ideally, grasslands should be burned biennially and grazed moderately.

Bibliography: leaves 87-93. / The Wattled Crane Grus carunculatus is a globally endangered resident of sub-Saharan Africa (Figure 1.1, Collar and Stuart 1985). The total population of Wattled Cranes is poorly known and estimates vary widely (Table 1.1). In 1985, Urban (1988) estimated the population at about 13 000 - 15 000 birds, while the IUCN (The World Conservation Union) Red Data Book suggested a total population of only 7 000 (Collar and Stuart 1985). Urban (1996) again estimated the total population at about 13 000 - 15 000 birds, but with a markedly different distribution among range countries. Most recently, regional surveys coordinated by the International Crane Foundation and South African Crane Working Group indicate a total population of aonly about 8 000 birds (R.Beilfuss in litt.).

Includes bibliographical references (leaves 98-107).

Includes bibliographical references (leaves 95-103). / It is believed that studies on individual species populations are important to gain a full understanding of ecosystem dynamics and that data gained from these studies can be incorporated into complex but meaningful models. This approach was adopted in a study of the complex kelp bed ecosystem off the west coast of South Africa initiated in 1975. Pilot studies indicated which plant and animal species should receive particular attention and several workers engaged in detailed studies of population dynamics and ecological energetics (Greenwood, 1974; Muir, 1977; Shafir, 1978; Dieckmann, 1978; Griffiths and King, 1978). A feature of the kelp bed system is that large masses of plant material are exported due to the heavy wave action experienced (Field et al., 1977; Velimirov et al., 1977). Attempts have been made to trace the fate of the kelp which is exported to adjacent beaches. A study by Muir (1977) showed the importance of kelp debris for the sandy beach amphipod Talorchestia capensis. The present study concerns the population dynamics and energetics of the supralittoral rocky shore kelp-eating isopod Ligia dilatata Brandt.

Bibliography: pages 85-87. / The size of the South African anchovy and pilchard population was estimated using Virtual Population Analysis (Gulland 1965). These estimates were used to test classical stock recruit models as well as to investigate possible stock interactions. The population biomass of the pilchard indicated a severe decline after 1959 from a level of approximately 2 000 000 metric tons to about 200 000 metric tons in the mid 1970's. This change was in agreement with catch per unit effort estimates of abundance (Newman et al in press). The anchovy abundance remained fairly constant at about 300 000 metric tons during the period 1965 - 1974 for which estimates could be made. During 1976 the pilchard stock showed a partial recovery of its former abundance. Adult and recruit stocks of both anchovy and pilchard were fitted to the Ricker (1954) and Beverton and Holt (1957) stock/recruit curves, but there was insufficient data to allow a decision to be made as to which model was appropriate for either stock. The anchovy and pilchard populations or age groups within them do not appear to interact in a very definite manner. Attempts to quantify interactions using Virtual Population Analysis have not been successful although better estimates of the strength of age-groups would be possible if the variation in natural mortality with age was understood. The fact that elements of the stock of anchovy and pilchard do not appear to be rigorously related indicates the importance of understanding which environmental factors are critical to survival. A difference between the area in which recruitment takes place and the area in which most adults are caught indicates a movement of young fish onto the west coast fishing grounds. The movements were substantiated by observations of catch per unit effort of juveniles on the west coast in each month of the fishing season.

Bibliography: pages 118-131. / Temporal and spatial changes in the abundance and distribution of anchovy and sardine eggs and larvae in the southern Benguela ecosystem were investigated during 14 cruises over 2 consecutive summer upwelling seasons as part of the South African Sardine and Anchovy Recruitment programme (SA-SARP). Cruises were conducted each month between August 1993 and March 1994 (SARP I) and September 1994 and March 1995 (SARP II). Anchovy spawning was largely confined to the western Agulhas Bank, reaching a definite peak during spring (October and November). Sardine ·spawning extended up the west coast ·duiing·periods when anchovy spawning reached a peak on the western Agulhas Bank. However, sardine eggs were dense on the western Agulhas Bank during peak spawning activity which appears to be bimodal, reaching a peak in the early spring (August/September) and again in late summer (February). · Although the midshelf region on the W AB appeared to be the centre of both anchovy and ·sardine spawning in the southern Benguela ecosystem, these data suggest that anchovy and sardine spawning activity may be both spatially, and temporally separated to some extent. Mean anchovy egg densities on the W AB decreased by 53 % from 1993/94 to 1994/95 while a slight increase in mean sardine egg density (16 %) over the entire region was observed from one season to the next. Lloyd's Patchiness Index was used to investigate the distribution patterns of spawning products and the results showed that the distribution of both anchovy and sardine eggs and larvae was extremely patchy, but that the eggs of both species were more patchy than their larvae. Anchovy eggs were most abundant at sea surface temperatures ranging from 16-20°C. Changes in the extent of 16-l 9°C water (as a measure of spawning habitat) and the abundance of large copepods within this region reflect intra-annual changes in the intensity of anchovy spawning activity. Sardine eggs were found predominantly in water of between 14.5-21.5°C. The seasonal intensity of sardine spawning appears to vary independently of the area of 16-19°C water, but· a positive correlation between the spawning activity of sardine and the monthly chlorophyll a concentrations on the W AB suggests that spawning may be related to their feeding conditions. A comparison of egg and larval distributions with current features from selected months during SARP supports previous studies which indicate that the frontal jet plays an important role in the transport of the early life history stages of anchovy and sardine but that the position of such transport can vary between the 200 m and 500 m isobaths. Areas of possible egg loss included the W AB, the offshore currents which can develop west of the Cape Peninsula and the outer branch of the jet off Cape Columbine. However, there is evidence that onshore currents further north may transport the eggs back to the region of the jet. The monthly estimates of anchovy egg mortality were highly variable and imprecise and these results were probably due to a combination of small sample sizes and reduced egg abundances, usually encountered at the start and end of the anchovy spawning season. The annual estimates of anchovy egg mortality during November between 1984 and 1994 were positively correlated with the patchiness of anchovy eggs during the same cruises. The effect of cannibalism in areas where eggs are particularly dense was invoked as a possible explanation for this result. It was concluded that the spawning behaviour of anchovy and sardine may be influenced by sea surface temperatures, feeding conditions for adult fish and advective processes in the southern Benguela ecosystem and these factors were discussed in terms of their possible impact on recruitment.