Browsing by Subject "Zoology"

Now showing 1 - 20 of 398
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    Activity patterns of baboons (Papio ursinus) at Cape Point
    (1976) Davidge, Christine; Siegfried, W R
    Four troops of chacma baboons Papio ursinus, comprising approximately 150 individuals, have home-ranges largely in the Cape of Good Hope Nature Reserve. One hundred and twenty-one days of observation was made of one of these troops, 0 troop, between March 1975 and February 1976. 0 troop occupies a home-range of roughly 4000 ha, using nine different sleeping cliffs. Troop members were observed most frequently throughout the year in a 45 ha core area containing one sleeping cliff. The troop showed no clear habitat preferences, but occupied alien Acacia thickets and Upland Mixed Fynbos more frequently than expected from the spatial distribution of these vegetation types in the home-range. Frequency of baboon occupation for each of five vegetation types varied seasonally, and appeared to be a reflection of the availability of plant food.
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    Acute and chronic effects of ammonia in the South African abalone, Haliotis midae Linnaeus (Mollusca)
    (2006) Reddy-Lopata, Kasturi; Moloney, Coleen; Cook, Peter; Lopata, Andreas
    Ammonia is the major end-product of protein catabolism in abalone, and is excreted into the surrounding water. Build-up of ammonia in abalone aquaculture systems can reach high toxic levels and impact negatively on farming operations. Ammonia levels therefore have to be regulated. Accurate estimates of toxic un-ionized ammonia (FAN) from the total ammonia nitrogen (TAN) measured by photometer test kits is crucial as inaccuracies could result in major losses of abalone on the farms. The accuracy and applicability of two frequently used photometer test kits (the Nesslers method and the Palintest method) were compared. The calculated TAN concentrations were regressed against the prepared standard ammonia concentrations in seawater for both methods. The predicted slope (β = 1) if the methods were 100% accurate was compared to observed slopes using the Nesslers (β=0.8327) and Palintest (β = 0.7507) methods. Both these test kits underestimated the TAN concentrations, but the Nesslers method was more accurate. Nitrites and nitrates are toxic to abalone at much larger concentrations than ammonia and exist at low concentrations in natural systems, therefore the sensitivity of their tests was not as important. Nitrites and nitrates were monitored using the Ferrous sulphate method and the Cadmium reduction method, respectively.
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    Adaptation to the host-plant, and the evolution of host specialization, in 'cycad weevils' (Coleoptera: Brentidae)
    (1991) Donaldson, John Sidney; Moran, V C; Hoffmann John
    This thesis deals with host relationships in an enigmatic and seemingly primitive group of weevils belonging to the genus Antliarhinus (Coleoptera: Brentidae). These beetles occur only on species of the cycad genus Encephalartos and appear to retain an ancient association with cycads, a group of plants that were widespread in the Mesozoic era (ca. 200 MYA) before the rise of the angiosperms and which are now represented by 11 genera with relict distributions in the tropics and sub-tropics. The primary aim of this research was to determine the possible causes of narrow host specialization in Antliarhinus zamiae (Thunberg) and A. signatus Gyllenhal, two species which develop exclusively on the ovules of their cycad hosts.
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    The African penguin Spheniscus demersus : conservation and management issues
    (2011) Waller, Lauren; Underhill, Les
    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.
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    Age, growth, reproductive biology and diet of Spondyliosoma emarginatum (Cuvier 1830) in the West Coast National Park, South Africa
    (2005) Fairhurst, Lucinda; Moloney, Coleen; Attwood, Colin; Durholtz, Deon
    Comprehensive morphometric measurements and counts, external colouration, reproductive behaviour and diet of steentjies (Spondyliosoma emarginatum) in Langebaan Lagoon were recorded between September 2004 and February 2005. Sagittal otoliths were extracted and age estimates recorded from both whole and sectioned otoliths in order to estmate growth and mortality parameters. A total of 302 steentjies (139-312 mm fork length) was sampled of which 243 were females, 55 were males and four were individuals with hermaphroditic gonads. Macroscopic and microscopic examination of gonads and monthly gonadosomtic indices suggest a spring spawning season and that steentjies are protgynous hermaphrodites with males significantly than females (t = 64.75, df = 301, p < 0.001). During the reproductive season, males develop a blue colouration. All males with this colouration had testes classified as either active or ripe and had significantly larger gonad masses than those without mating colours (U = 3.5, Z = 6.48, p $lt; 0.001). The length-at-50%-maturity for females was 171 mm (FL) and for males was 204 mm (FL). The size at 50% sex change was estimted as 250 mm (FL). Analysis of foregut contents showed steentjies to be opportunitistic ominivores, changing from plant to animal food as they age. The average percent error and coefficient of variation values for whole otoliths were 4.59% and 6.00% respectively, and 10.89% and 14.53% for sectioned otoliths. Although the result of the whole otolith study provided more precise age estimates, there was a strong indication of bias so the sectioned otolith results were used for calculating the growth model. Growth (by sex) was modelled using a model developed for sex changing sparids that allows for accelerated growth after sex change. Steentjies appear to have shorter life spans than most sparids; the oldest individuals sampled attaining less than 7 years of age. Growth rates appear to be relatively high. The smallest, youngest fish were all female, with males only present in the larger size classes. The estimated mortality for steentjies was 0.7y[-1]. Such a high mortality rate implies that further increase in fishing pressure on this species may not be sustainable in Langebaan Lagoon.
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    An ecological study of the macro-invertebrate fauna of the Eerste River, Western Cape Province, South Africa
    (1982) King, Jacqueline Mary; Branch, George
    The Eerste River is situated in the south-western Cape Province, South Africa. Its upper reaches have a stony substratum, and can be divided into three physical/biotic zones: The Mountain Stream, Upper River and Lower River zones. Investigations of the abundance, biomass, species diversity and species composition of the benthic macro-invertebrates in the three zones were carried out in 1975/76. Spatial and temporal changes in these factors can be correlated with changes in the physico-chemical quality of the water. Abundance and biomass generally increased downstream, but were low below a dam construction-site, because of the blanketing effects of silt on the substratum. Seasonal changes in abundance and biomass differed in the three zones, but always included a peak in spring. The highest values of both were in the Lower River in summer, reflecting the build-up of organic pollutants there during times of low flow. Diversity of the Ephemeroptera, which was felt to be representative of a change in.diversity of the fauna as a whole, generally decreased downstream, with a major drop at the town of Stellenbosch, and another at a sewage-farm outfall. A misleading increase in diversity occurred, however, in the silt-laden waters below the dam site,. due to the fleeting occurrence of individuals of several different species. Composition of the fauna was typical of local rivers with mountain sources. Figures for abundance, biomass and calorific values of species are given in appendices
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    An investigation of diet management strategies for the culture of the South African abalone, Haliotis midae
    (1996) Simpson, Brynn James Alric; Cook, Peter
    The Far East provides an almost insatiable market for a wide variety of seafood products. Abalone are one of the more sought after delicacies of the East due to the subtly flavoured meat. Abalone are imported from around the world and command high prices. Throughout their global distribution, many of the I 00 or so species of abalone are commercially and recreationally exploited. The continuing demand for abalone has resulted in the overexploitation of wild stocks throughout the world. ·Most commercial abalone fisheries are characterised by high yields at the beginning of the fishery, followed by a subsequent decline in yields to present levels (Ebert, 1992; Tarr, 1992). Abalone culture was pioneered in Japan, partly as a consequence of overexploitation, through the development of reseeding programmes.· Hatchery-reared abalone were reseeded into depleted wild abalone populations, and are now harvested sustainably by •· i local fishermen (Shaw, 1982). Similar ventures have been investigated for Haliotis tuberculata by Cochard and Flassch (1981), H. rufescens by Ebert and Ebert (1988) and Tegner and Butler (1989), H. kamtschatkana by Emmet and Jamieson (1988), and H. iris by Schiel (1993). In addition to reseeding programmes, abalone culture has provided new products for the Far East seafood markets. Abalone are exported live from several countries, as 'cocktail abalone' and command prices in excess of those paid for canned or frozen abalone (Rudd, 1994). H. midae is highly sought after in the Far East (Rudd, 1994). In South Africa, wild populations of abalone have been commercially exploited since 1949 (Tarr, 1992). The only abalone of commercial value is Haliotis midae, which is distributed between St Helena Bay (320 45'S~ 180 IO'E) on the West coast and just Chapter 1. Introduction 2 north of Port St Johns (31 o 40'S; 2.90 35'E) on the East coast of South Africa (Wood, 1993). H. midae is most abundant between St Helena Bay and Cape Agulhas (Barkai and Griffiths, 1986) and supports a commercial fishery between Cape Columbine and. Quoin Point (Tarr, 1992). A small commercial fishery exists at Hamburg on the East coast of South Africa (Wood, 1993). Research into culture of the South African abalone began in the last decade, encouraged by the decline in wild abalone populations and the development of a market for cocktail sized abalone. Initially abalone culture was not considered to be viable in South Africa, largely due to a lack of knowledge. The initial breakthrough in the culture of H. midae followed the demonstration that it was possible to spawn wild abalone through chemical cues (Genade et al., 1988). The realization that the spawning and culture of H. midae was possibl~ prompted further research into abalone culture. At present there are approximately 10 commercial companies involved in the preliminary stages of abalone culture in South Africa. Globally, research has covered many aspects of abalone culture. In the present study, various aspects of growth and nutrition of cultured H. midae were researched.
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    An analysis of factors controlling the distribution of zooplankton in the Knysna estuary, South Africa
    (1987) Veldhuis, Helen Anne; Griffiths, Charles L
    The Knysna estuary system, on the south coast of South Africa, was sampled for zooplankton over period of one year. All species were recorded and an attempt was made at relating the distribution of populations to physical factors within the estuary. Over 50 species were identified. Pseudodiaptomus hessei, Acartia(Paracartia) longipatella and A.(Acartiella) natalensis were the dominant copepods in the upper estuary. Paracalanus spp. were dominant near the mouth. Zooplankton distribution was found to be related to tidal exchange. The zooplankton displayed a seasonal cycle of abundance, with maximum numbers occuring during summer. P. hessei displayed no pronounced seasonal cycle in abundance. Its abundance was strongly related to freshwater inflow. Seasonal succession was evident between A. natalensis, the summer dominant, and A. longipatella, the winter dominant. The controlling factors for this cyclical dominance were not clear. Diel vertical migration behaviour was shown to various degrees by virtually all zooplankton populations. The stimulus for this behaviour could not be definitely identified.
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    Animal-habitat relationships in the Knysna forest : discrimination between forest types by birds and invertebrates
    (1985) Koen, Julius Heinrich; Crowe, Timothy M
    Some silvicultural practices in the Knysna Forest are aimed at the sustained-yield production of valuable timber tree species, albeit on limited areas only. This study investigates effects of forest plant species composition and physiognomy on bird and invertebrate communities in three discrete, relatively undisturbed forest types along a dry-wet soil moisture gradient. Using discriminant functions analysis, a 100% floristic and a 78% vegetation structural discrimination was obtained between the three forest types. However, the bird communities of these floristically and structurally different forest types were very similar in species composition and had much lower densities than normally encountered in other superficially similar forests. It was only possible to discriminate between the wet and the moist/dry forest types by using the two best bird discriminators. the blackheaded oriole (Oriolus larvatus) and the sombre bulbul (Andropadus importunus). A separation of the moist and dry forest types was not possible. Although an 81% discrimination between forest types was attained through analysis of ground surface invertebrates. measures of litter and aerial invertebrate abundance were of limited use as discriminators. Historical and biogeographic factors and the low nutritional levels in the soil and vegetation may be the cause of low bird and invertebrate density and diversity. It is concluded therefore, that floristics and vegetation structure have, at best, a minor influence on bird community structure, and possibly also on the invertebrate community in the Knysna Forest and that management practices need not cater for variation in forest vegetation composition and physiognomy. Bibliography: pages 49-59.
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    Antarctic sea ice trends and its response to the Southern annular mode
    (2009) Collins, Charine
    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.
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    Anti-predator behaviour of Cape fur seals Arctocephalus pusillus pusillus in relation to predation by white sharks Carcharodon carcharias around Seal Island, False Bay, South Africa
    (2010) De Vos, Alta; O'Riain, Justin
    How predators affect the behaviour of their prey is one of the most studied subjects in behavioural ecology, with many hypothesis and models explaining how animals should behave and even more descriptive studies detailing how they do. The unification of the empirical with the theoretical, however, remains limited. The overall aim of my thesis was to address this paucity at Seal Island, South Africa, where recently quantified patterns of predation pressure by white sharks Carcharodon carcharias on Cape fur seals Arctocephalus pusillus pusillus suggested a landscape of fear particularly apposite to this.
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    Approaches to assessing the status of nearshore and estuarine fish and fisheries and their responses to environmental change
    (2008) Lamberth, Stephen Justin; Branch, George M
    In multispecies fisheries knowledge, personnel and funding limitations often create the dilemma over which species should be the first to receive management and research attention. This thesis uses a Multi-Criteria Decision Analysis approach to prioritize 176 South African linefish species on the basis of a number of criteria indicating conservation and socio-economic importance. Each species importance was assessed from the points of view of (1) conservation, (2) each fishery sector separately and combined and (3) the overall combined conservation and sectorial importance. Relative scores within each of the fishery sectors were dominated by two or three species such that the scores separating the remaining species from each other were small. On the whole, the top species included those most important in each sector, biogeographic region and in terms of conservation. The separate and overall ran kings should assist in the development of broadly acceptable management strategies for different fish. Catch data for 129 of 255 functional estuaries on the South African coastline were reviewed and the relationships between fish catch and estuarine size, type and biogeographical region analysed using simple and multivariate models. Estuary size alone explained over 80% of the variation in catch in the warm temperate region and over 90% of the variation in catch in the cool temperate and subtropical region. Further analysis of the two main estuarine types (permanently open and temporarily open/closed estuaries) revealed higher productivity for the permanently open systems. Both estuarine size (ha) and type (5 types) were used to explain catches using general linear models. The models were able to explain 82-98% of the variance in catches. The total estuarine catch in South Africa was estimated at 2 480 tons per annum with a total value of R748 million, of which 99% could be attributed to recreational angling. Estuarine contribution to the inshore marine fisheries was estimated at approximately R846 million per year with estuarine dependent species comprising 83% of the catch of the recreational shore and commercial seine and gillnet fisheries and only 7% of the catch of the recreational spearfishery and commercial and recreational boat fisheries. Total value of estuarine and estuary-dependent fisheries was estimated to be R1.594 billion per annum in 2008 rands. The cool-temperate Olifants and warm temperate Breede estuaries on the west and south coasts of South Africa have both seen a >35% reduction in mean annual runoff (MAR) from a historical reference condition to the present day with a >60% reduction possible under future development. With almost no exceptions, the Olifants Estuary fish assemblage has seen an overall 20% decrease in abundance from reference to the present day and will gradually decline to 55% of reference with a predicted future 60% reduction in MAR. Consequently, future reductions in flow are likely to see the Olifants Estuary progressing towards a low biomass, low diversity, marine-dominated system. In contrast, with the exception of some key exploited species, fish abundance in the Breede Estuary has increased by 6% from reference to the present day and is likely to increase to 115% of reference with future reductions in flow. In all, the fish assemblage will experience a gradual change from a relatively high-diversity low-abundance freshwater-rich system under historical flow conditions to a high-diversity, highabundance, marine-dominated system with future reductions in flow.
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    Aspects of marine fouling in western Cape waters
    (1981) Henschel, Johannes Robert; Buys, M E L; Branch, George M
    Two independent investigations into aspects of marine fouling were conducted in Simonsbay and Table Bay during 1979 to 1981. The development of macrofouling communities on six test materials was examined at 10m and 20m depths in Simonsbay for periods ranging from one month to one year. Community development was similar on inert non-reactive materials, aluminium, stainless steel, fibre glass and polyvinylchloride, but was reduced on non-wettable silicon rubber and corrodible mild steel. Macrofouling was characterized by seasonal succession with minimum colonization rates during winter, when adverse weather and low temperature conditions prevailed. The nature of fouling differed with depth. At 10m depth, mussel and barnacle-dominated communities developed rapidly, while at 20m depth, ascidian and barnacle-dominated communities developed more slowly. The role of primary film formation in the colonization of substrata by invertebrates was investigated in short-term studies conducted in Simonsbay and Table Bay. Surface-bound antibiotics, streptomycin and penicillin, were used to inhibit bacterial proliferation, while a herbicide, diuron, was employed to prevent diatom growth. The colonization by invertebrates was monitored on these surfaces and compared to surfaces where primary film development was normal, or where it was advanced by pre-culturing in laboratory seawater. It was found that invertebrates attached soon after panel exposure and that differences in the degree of primary film development were of little consequence to their settlement. The apparent discrepancy of these observations with previous findings is discussed, with special reference to the location of test sites in relation to mature communities.
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    Aspects of physiology of the angulate tortoise, Chersina angulata, with special emphasis on the influence of body size
    (1988) Armstrong, Adrian
    Until recently not much of the physiology of the angulate tortoise had been investigated, and the work done focused on its thermoregulation (Craig 1973; Perrin & Campbell 1981). However, during the last few years research dealing with more of its thermoregulation and water relations was begun (S. Els pers. comm.). This study aims to examine the relationships between body size and the rates of resting metabolism, evaporative water loss and heat transfer. The relationship of the changes in certain physical properties to the corresponding changes in physiological properties, due to increases in body size, will be investigated. Aspects of a theory of biological similarity will be discussed in the light of the results. Other physiological processes, such as respiration and assimilation efficiency, will be looked at without reference to body size.
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    Aspects of pollution in False Bay, South Africa (with special reference to subtidal pollution)
    (1992) Rundgren, Carl David; Brown, Alec C
    False Bay is the largest (circa 1000km²) natural, coastal embayment on the South African coastline and is located between latitudes 34°04'S and 34°23'S and longitudes 18°26'E and 18°52'E at the southern tip of Africa, near Cape Town, South Africa. The semi-enclosed nature of the bay makes it unsuitable as a 'sink' for all the contaminated urban stormwater run-off and the greatly increased pollution loads entering the bay. All pollution point sources entering False Bay were identified and described, and some of these selected for detailed study, the emphasis being on the impact of some individual discharges on the subtidal macrofauna. The similar biotic characteristics of three subtidal study sites in the region of the Steenbras Water Treatment Plant discharge indicate that the general turbidity and lower salinity characteristics of eastern False Bay are more likely to be responsible for the impoverished diversity near the outfall rather than the aluminium content of the discharge. Toxicity experiments on the bivalves Choromytilus meridionalis, Mytilus galloprovincialis and Perna perna using alum and ferric sludge indicate that there are no significant short-term sub-lethal toxic effects on the rocky shore bivalves and that decreased salinities in the immediate region of the outfall (as a result of the freshwater stream input) may have a more deleterious effect. A study of eighteen subtidal sites in False Bay indicated that overall densities of subtidal macro plastic debris were low, but that there are some 'hot spots' where densities are relatively high viz., Kalk Bay, Strandfontein, Mnandi, Monwabisi and Gordon's Bay. Colonising of debris by benthic organisms does occur, mostly on white plastic. Most of the debris consisted of plastic packaging from local land-based sources, indicating that it originates from wind-blown litter left by beachgoers. The highest density at the Sunnycove Control Site occurred in January during the peak holiday season. A longer term (three years) study of the subtidal environment in the vicinity of the Marine Oil Refiners outfall pipe indicated that the lack of subtidal macro fauna is more likely due to the harsh environmental conditions (abrasion and smothering) rather than the pollution impact of the outfall. This is confirmed by the abundant, healthy and diverse community on the nearby wreck of the Clan Stuart (1917) which indicates a stable ecosystem. The complexity of False Bay - its unique topography, bathymetry, meteorology make it difficult to attain a true climatic or average circulation. This lack of a consistent conceptual overview of the False Bay physical circulation is a short-coming that needs to be urgently addressed if the dangers of pollution inputs are to be accurately assessed. An overall management policy for False Bay should be urgently formulated and an officially constituted body with legislative power is needed if holistic management of the bay is to be achieved and such a prime recreational asset preserved for future generations. Bibliography: pages 195-225.
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    Aspects of stress with particular reference to mytilid mussels and their parasites
    (1999) Webb, Stephen Charles
    Eight new species of digenea were found in a survey of Aulacomya ater, Choromytilus meridiana/is, Perna perna and Mytilus galloprovincialis. Metacercaria notobucephala sp. nov., a bucephalid from Choromytilus has locality-specific prevalences ranging from 0.23% to 4.46%. It is a severe reproductive stress and reduces the sperm count by a factor of 1000. Metacercaria notobucephala also causes Choromytilus to lose ninhydrin positive substances. The gymnophallid Metacercaria perchorupis sp. nov. occurs in 90.7% to 100% of Choroinytilus and in 74.83% of Perna. Metacercaria A sp. nov., a renicolid, occurs in 78.86'yo to 90.33% of Choromytilus and 44.74% of Perna. Metacercaria B sp. nov., a lepocreadid, infects from 18.3% to 43.17% of Choromytilus and 3.51% of Perna. The combined effect of these three digenea causes 10% of the variation in emersion survival time of male Choromytilus (P = 0.02). Longer surviving mussels had fewer cysts; this suggests that these parasites constitute a somatic stress. Metacercaria columbinesis sp. nov., a zoogonid, was found in 28.6% of Mytilus. The fellodistomid Metacercaria maculatopsis sp. nov. occurred in 0.4% of Choromytilus. The gymnophallid, Metacercaria ater sp. nov. was found in 0.125% of Aulacomya. A rapid technique of semi-permanent staining and fixing with acetic orcein was developed to aid the description of these worms. Juvenile pycnogonids, Nymphonella sp., were found in 0.15% to 7.5%. ofChoromytilus. Nemerteans, nematodes, copepods, polychaetes and other minor symbionts are quantified in these mussels. Mastigocoleus sp., a shell boring cyanophyte, colonises Mytilus with prevalences from 1% to 94% and can reduce shell strength by 43%. The relationship between stress (amount of alga on the shell) and strain (degree of damage) is demonstrated: 61.8% of variation in damage is attributable to the extent of infection (P = 0.001). Stress is defined as an agent that reduces the fitness of the organism. The degree of reduction is termed strain. Fitness is an ontological statement about the organism. Schemes are proposed for rendering these concepts operational. Individual and ecosystem concepts of stress are not homologous and therefore cannot be substantively integrated. In contrast, psychological and physiological stress are deemed integrable: a scheme for this is proposed. Physical (salinity), chemical (ammonia & phenol) and biological agents (scavenging whelks) are shown to be substantively integrable as stresses since they all inhibit shell gaping and byssus production. Mussels demonstrate clear and appropriate closure responses when in the presence of salinity, ammonia levels and Burnupena: all agents that are likely to be of historical selective significance. In contrast, phenol, an unfamiliar agent, elicits an inconsistent response. It is hypothesised that this difference may help distinguish natural stresses from synthetic pollutants. As predicted, the valve opening dynamics of heat stressed mussels were qualitatively and invariably different from those of non-lethal voluntary movements. Dying dynamics have increasing velocity; voluntary dynamics show maximum velocity initially. Analysis of stimuli effects, often interpreted as eustresses, show that assays covering distal as well as proximal effects and those that tend towards whole body integrations are more likely to detect the agent as deleterious. Thus any notion of positive deflections or eustress must be treated with great caution and subject to longer term tests and with more complete integrations if it is to be accepted.
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    Aspects of the behaviour and ecology of White-fronted Sandplovers and Sanderlings on a South African sandy beach
    (1986) Crowe, Anna Aletta; Siegfried, Roy
    The dissertation comprises a general introduction, five chapters and a summary-synthesis which is designed to link the chapters into a cohesive account. Chapter 1 deals with the avian population of a southwestern Cape sandy shore and compares this population with those of sandy beaches in the eastern Cape and Natal. The abundance of birds and the estimated energy requirements of the avian populations in these three geographical areas increase during the austral summer, due to an influx of migrants from the northern hemisphere. The proportion of migrants to residents varies geographically, being greater in the southwestern Cape and Natal than in the eastern Cape. Chapter 2 summarizes information on the systematics, global distribution and morphology of two small shorebirds, the White-fronted Sandplover Charadrius marginatus and the Sanderling Calidris alba, which are identified in Chapter l as being dominant components of the southwestern Cape sandy shore avian population. Chapter 3 reports on the spatial and temporal use of the intertidal habitat by foraging White-fronted Sandplovers ·and Sanderlings. Interactions between these two species are discussed in the light of competition theory. The foraging ecology of the Sanderling and White-fronted Sandplover at Ouskip differed strikingly. Although both species exhibited a tidal cycle in foraging activities, rather than a diurnal cycle, White-fronted Sandplovers tended to feed during the latter half (i.e. mid to high tide), whereas Sanderlings fed during the first half (i.e. low to mid tide) of the tidal cycle. Both species' foraging activity also varied spatially and seasonally. White-fronted Sandplovers fed primarily in drier microhabitats above high tide level, and Sanderlings in wetter microhabitats near the water's edge. In Chapter 4, the size and structure of Sanderling flocks are described. The frequency distribution of flock sizes of wintering Sanderlings foraging on the sandy beach at Ouskip was bimodal, with a peak at small flock sizes and another at large flock sizes. It is hypothesized that large groups of Sanderlings consist of individuals searching for subterranean prey, and that small groups consist of subsets of these larger groups which have located food patches. Chapter 5 is an analysis of breeding periodicity in White-fronted Sandplovers in southern Africa, and focuses on the relationships between geographical and year-toyear variation in breeding activity and rainfall patterns, food availability and the possible effects of competition with migrant shorebirds. This species exhibits significant geographical variation in breeding season, and significant year-to-year variation within an area which has winter (May - August) rainfall. There was no year-to-year variation in breeding season within an area with summer (November - February) rainfall.