Browsing by Author "Siegfried, W R"

Now showing 1 - 10 of 10
  • Thumbnail Image
    Item
    Open Access
    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.
  • Thumbnail Image
    Item
    Open Access
    Behavioural ecology of lesser sheathbills Chionis minor at Marion Island
    (1980) Burger, Alan Eckard; Siegfried, W R
    Adaptations to island life have seldom been studied in birds outside temperate or tropical regions. Lesser Sheathbills Chionis minor (Charadriiformes; Chionididae) were studied at Marion Island (46°54'S, 37°45'E) and the ways in which their feeding ecology, breeding biology and social behaviour were adapted to existence on a sub-Antarctic island were assessed. The birds' reproductive output and post-fledging survival rates were estimated and probable factors limiting the population examined. Seasonal and spatial variations in the diet and foraging habits were related to the quality, availability and distribution of food, and the effects of interspecific competition, the weather and predators. The adaptiveness of the broad trophic niche was investigated. A hypothesis that the variable social behaviour facilitated exploitation of variable food resources to benefit individual birds was examined; particular attention was paid to territoriality among breeding (summer) and non-breeding (winter) adults within penguin colonies and flocking amongst birds foraging on the coastal plain. Time and energy budgets of birds feeding in these habitats were drawn up. Displays by Lesser Sheathbills were described and their functions in territories, flocks, at nest sites and in sexual interactions were quantitatively assessed.
  • Thumbnail Image
    Item
    Open Access
    Co-existence in the Phoebetria albatrosses at Marion Island
    (1977) Berruti, Aldo; Siegfried, W R
    The aims of the present study are threefold. Firstly, the coexistence of the two closely related, normally allopatric, albatross species is investigated in their zone of overlap where interspecific competition for food resources and nesting space is likely to be most acute. Secondly, the genetic isolation of the two species is investigated, as co-existence implies increased interspecific social interaction with associated increased possibilities of hybridization. Thirdly, the two species' possible evolutionary histories are examined in relation to their ecologies. Logistical constraints prevented study of fusca and palpebrata on the feeding grounds, i.e. at sea, and feeding could be studied only indirectly.
  • Thumbnail Image
    Item
    Open Access
    Conservation implications of the invasion of southern Africa by alien organisms
    (1991) Macdonald, Ian Angus William; Siegfried, W R; Moll, EJ
    Alien species known to be invading untransformed ecosystems in southern Africa, and, more particularly, those inside nature reserves, were identified. The extent and ecological impacts of these invasions were assessed. Their control within reserves was also evaluated. Research approaches used were; literature review (which included an international review), a detailed questionnaire survey of alien plant invasions in 307 reserves, rapid field surveys of 60 reserves, intensive case studies of four reserves (Cape of Good Hope Nature Reserve, Hluhluwe-Umfolozi Game Reserve, Kruger National Park, Pella Fynbos Research Site), international comparison with case-study reserves in other savanna and Mediterranean-type biomes, and field evaluation of control methods for alien plants in the two fynbos reserves. Ecological impacts of alien invasions throughout the subcontinent were determined from historical changes in vertebrate populations, including detailed studies of three native birds (Bostrychia hagedash, Lybius leucomelas, Ploceus velatus) expanding their ranges, partly in response to the spread of invasive alien trees. The results are presented in eight chapters, comprising 26 published (or submitted) papers, an introduction and a concluding summary. One chapter covers contributions to the theoretical understanding of invasion processes, including a prediction of their interaction with rapid global environmental change. The conclusion is reached that alien invasions pose a serious challenge to nature conservation in the region. Mostly this comes from alien woody plants but the importance of herbaceous plants has possibly been underestimated regionally. Introduced mammalian pathogens and predatory fishes have also had important effects. Alien invertebrates have been poorly studied (the ant lridomyrmex humilis poses a significant threat). Alien terrestrial vertebrates have generally had only localized effects. Alien plant invasions affect all biomes, with riparian ecosystems being regionally threatened. Mesic biomes and habitats are usually more invaded by alien plants than xeric equivalents. 281 alien vascular plant species were recorded invading vegetation within nature reserves (an average of 12 species per reserve) with an additional 200 species being possibly present but unrecorded (an average of 18 species per reserve). By 1984, the 54 plant taxa recorded invading reserves most frequently were estimated, on average, to be present in 30% of the 11cm x 11cm grid cells of the reserves they were invading. The average potential future extent of these invasions was estimated to be 51%. Control had, on average, been initiated for two plant species in each reserve and 18% of these operations had already resulted in complete eradication. Reported control costs were particularly high for the woody plants which pose a serious threat to the highly endemic flora of the fynbos biome, on average R48 284/reserve (R1,8/ha = US Dollar 1,2/ha) in 1983. These high costs were validated experimentally. A computerized optimization model, aimed at minimizing the costs of controlling the most intractable shrub invader of fynbos, Acacia saligna, was developed from the results of a field experiment at the Pella site. Practical field- scale control of these invasions was assessed to be feasible, using the results of repeated monitoring of permanent plots in the Cape of Good Hope Nature Reserve. Control strategies and regional priorities, based on the theoretical and practical insights gained from this study, are proposed. Even though the intensity of invasions is likely to increase in the foreseeable future, in part as a result of rapid man-induced changes in global climate, it is predicted that these invasions can be controlled if the correct approaches are adopted timeously. Failure to control them, will ensure that the extinction rate of native species will markedly increase and that ecosystem functioning will be altered significantly at a local scale and, conceivably also, at a regional scale.
  • Thumbnail Image
    Item
    Open Access
    Ecological energetics of Eudyptes penguins at Marion Island
    (1987) Brown, Christopher Raymond; Siegfried, W R
    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.
  • Thumbnail Image
    Item
    Open Access
    Ecological segregation of burrowing petrels (Procellariidae) at Marion Island
    (1984) Schramm, Michael; Siegfried, W R
    1. Eight burrowing petrel species were found nesting within the area studied in north-eastern Marion Island during April 1979 to May 1980. These were Salvin's Prion Pachyptila vittata salvini, Blue Petrel Halobaena caerulea, Greatwinged Petrel Pterodroma macroptera, Kerguelen Petrel Pterodroma brevirostris, Softplumaged Petrel Pterodroma mollis, Whitechinned Petrel Procellaria aequinoctialis, Grey Petrel Procellaria cinerea and South Georgian Divingpetrel Pelecanoides georgicus. Eighty-one percent of burrows found belonged to Salvin's Prions. 2. The nest site preferences of Salvin's Prion, Blue Petrel, Greatwinged Petrel, Kerguelen Petrel, Softplumaged Petrel and Whitechinned Petrel were investigated. These species had individual preferences with respect to soil depth, soil moisture content, slope angle or slope aspect. 3. The Kerguelen breeding biologies and diets of Greatwinged Petrels, Petrels and Softplumaged Petrels were studied. The species bred at different times of the year with non-overlapping chick-rearing periods. Incubation periods were similar but, relative to adult size, Kerguelen Petrel chicks grew fastest. All three species took mainly cephalopods although Kerguelen Petrels took the most crustaceans and fish. 4. Subantarctic Skuas Catharacta antarctica were important predators of petrels. They preyed upon whatever petrel species were most abundant in an area, although large petrels (Whitechinned Petrel) and those breeding in winter (Greatwinged Petrel) were seldom taken. 5. Similar petrel species had the bulk of their breeding populations spread over different habitats thus reducing any competition for nest space. At the same time, staggered timing of breeding, and particularly the non-overlapping chick-rearing periods of the three Pterodroma petrels, helped to minimize competition for food.
  • Thumbnail Image
    Item
    Open Access
    Ecology of the bald ibis Geronticus Calvus and fire in the South African grassland biome
    (1983) Manry, David Edward; Siegfried, W R
    The thesis comprises four separate chapters dealing with various aspects of the ecology of the bald ibis Gerontiaus aalvus (Aves: Threskiornithinae) and fire in the South African grassland biome. The use of habitat by foraging bald tbises, and the reproductive performance of bald ibises during three consecutive breeding seasons (1978-80) at a single breeding colony in western Natal, South Africa, are discussed in relation to rainfall, grass-burning, domestic livestock grazing and agriculture. A review follows dealing with the ecology of fire in the South African grassland biome, with particular reference to the possible role of lightning in the origin, maintenance and distribution of open grassland in South Africa under the natural fire regime. The four chapters composing the thesis are prefaced by a general introduction and followed by a general summary and conclusion.
  • Thumbnail Image
    Item
    Open Access
    Feeding ecology and habitat of the Protea seedeater Serinus leucopterus
    (1976) Milewski, Antoni Vincent; Siegfried, W R; Moll, EJ
    The present study involved a description of the habitat and the feeding niche (sensu Whittaker et. al. 1973) of the protea seedeater, and an assessment of factors contributing to the ecological segregation between the protea seedeater and its congeners in the south-west Cape biotic zone. No similar study of an African bird has been attempted.
  • Thumbnail Image
    Item
    Open Access
    The preservation of the Cape flora : status, causes of rarity, ideals and priorities
    (1992) Rebelo, Anthony G; Siegfried, W R
    The Cape Floristic Region (CFR), covering 90 000 km2, comprises one of the world's six floral kingdoms. With 8600 species, of which 68 per cent are endemic, it ranks amongst the richest of temperate and tropical floras. Although 19 per cent of the CFR occurs in nature reserves, by far the majority of the preserved area comprises Mountain Fynbos. Only 0.5 and 3 per cent of the original extent of Renoster Shrub/and Lowland Fynbos is preserved, respectively. In this study Fynbos vegetation is identified as the richest habitat for Red Data Book (RDB) plant, freshwater fish, amphibian, butterfly, and reptile species in southern Africa. The greater Cape Town metropolitan area is identified as containing by far the highest richness of RDB plant, butterfly, reptile and amphibian species in the CFR Thus, this area ranks globally as one of the most urgent conservation priorities. The study also illustrates that previously used methods for evaluating priority conservation areas have under-rated species-poor areas containing a high proportion of RDB species. By collecting for species richness, a far more realistic picture of threatened areas can be obtained from RDB taxa. This study predicts, using a priori hypotheses based on ecological traits, and finds, that seed dispersal and regeneration strategies are most strongly correlated with rarity, most specifically with distributional area. Using distributional data for the Proteaceae, this study estimates that 95 per cent of all vascular plant species in Fynbos can be preserved in 16 per cent of the area. It also identifies the sites that require preservation if the maximum protection of floral diversity is to be realized. Two null models for evaluating the efficiency of a spatial configuration of reserves are proposed. Utilizing an iterating selection procedure, this study explores various algorithms, based on species richness and rarity, to construct ideal reserve configurations. This study provides the first empirical confirmation that the ideal approach to designing a reserve configuration is to identify areas of high endemism and richness in distinctive vegetation types within particular biogeographical regions. Thus, this study pioneers the use of RDB data to identify priority conservation regions, provides one of the first assessments of the causes of rarity in plants and establishes useful null models and algorithms for the identification and testing of ideal reserve locations in the design of integrated reserve networks. Not only does this study contribute towards theoretical reserve selection procedures, but it provides one of the most advanced frameworks for the preservation of a top conservation priority in the world, the CFR.
  • Thumbnail Image
    Item
    Open Access
    Studies of herbivory and vegetation change in Karoo shrublands
    (1993) Milton, Suzanne Jane; Siegfried, W R; Rutherford, MC
    The broad objective of these studies was to view present landuse (extensive small stock ranching) in the Karoo against the background of relationships between indigenous plants and animals and to indicate how modification of herbivore regimes might affect this arid environment. Specific objectives were to determine how grazing by domestic livestock brings about vegetation change, why such changes are sometimes irreversible, and whether existing conceptual models of vegetation dynamics adequately explain the impact of domestic livestock on Karoo vegetation. Three interrelated aspects of plant-animal interactions were considered: the influence of herbivores on the evolution of Karoo plants, food selection by indigenotis and introduced herbivores and the effects of herbivory, competition and rainfall on plant reproduction and recruitment. The results of these investigations are presented as 14 papers. The first three papers interpret plant morphology and biogeography to provide information on past spatial and temporal use of the landscape by herbivores, and the next seven provide new information on food selection by invertebrates, indigenous vertebrates and by domestic sheep. Three papers examine the hypothesis that the reproductive output, survival and abundance of some Karoo plant species are influenced by herbivory. The possible consequences of various land management options on diversity and productivity of Karoo rangelands are discussed in the concluding paper. It was inferred, from biogeographic trends in the relative abundance of plants with thorns or propagules adapted for epizoochoric dispersal, that densities of large mammalian herbivores decreased from the north eastern to the southwestern Karoo. Within the most arid parts of the Karoo, mammalian herbivory appears to have been concentrated along drainage lines and in pans.