Browsing by Author "Cumming, Graeme"

Now showing 1 - 4 of 4
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    Avian malaria prevalence and mosquito abundance in the Western Cape, South Africa
    (BioMed Central Ltd, 2013) Okanga, Sharon; Cumming, Graeme; Hockey, Phillip
    BACKGROUND:The close relationship between vector-borne diseases and their environment is well documented, especially for diseases with water-dependent vectors such as avian malaria. Mosquitoes are the primary vectors of avian malaria and also the definitive hosts in the disease life cycle. Factors pertinent to mosquito ecology are likely to be influential to observed infection patterns; such factors include rainfall, season, temperature, and water quality. METHODS: The influence of mosquito abundance and occurrence on the prevalence of Plasmodium spp. in the Ploceidae family (weavers) was examined, taking into account factors with an indirect influence upon mosquito ecology. Mosquitoes and weaver blood samples were simultaneously collected in the Western Cape, South Africa over a two-year period, and patterns of vector abundance and infection prevalence were compared. Dissolved oxygen, pH, temperature and salinity measurements were taken at 20 permanent waterbodies. Rainfall during this period was also quantified using remotely sensed data from up to 6months prior to sampling months. RESULTS: Sixteen wetlands had weavers infected with avian malaria. More than half of the mosquitoes caught were trapped at one site; when this site was excluded, the number of mosquitoes trapped did not vary significantly between sites. The majority of mosquitoes collected belonged to the predominant vector species group for avian malaria (Culex culex species complex). Seasonal variation occurred in infection and mosquito prevalence, water pH and water temperature, with greater variability observed in summer than in winter. There was a significant correlation of infection prevalence with rainfall two months prior to sampling months. Mosquito prevalence patterns across the landscape also showed a close relationship to patterns of rainfall. Contrary to predictions, a pattern of asynchronous co-variation occurred between mosquito prevalence and infection prevalence. CONCLUSION: Overall, salinity, rainfall, and mosquito prevalence and season were the most influential vector-related factors on infection prevalence. After comparison with related studies, the tentative conclusion drawn was that patterns of asynchronous variation between malaria prevalence and mosquito abundance were concurrent with those reported in lag response patterns.
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    Bridge hosts, a missing link for disease ecology in multi-host systems
    (Springer, 2015) Caron, Alexandre; Cappelle, Julien; Cumming, Graeme; de Garine-Wichatitsky, Michel; Gaidet, Nicolas
    In ecology, the grouping of species into functional groups has played a valuable role in simplifying ecological complexity. In epidemiology, further clarifications of epidemiological functions are needed: while host roles may be defined, they are often used loosely, partly because of a lack of clarity on the relationships between a host's function and its epidemiological role. Here we focus on the definition of bridge hosts and their epidemiological consequences. Bridge hosts provide a link through which pathogens can be transmitted from maintenance host populations or communities to receptive populations that people want to protect (i.e., target hosts). A bridge host should (1) be competent for the pathogen or able to mechanically transmit it; and (2) come into direct contact or share habitat with both maintenance and target populations. Demonstration of bridging requires an operational framework that integrates ecological and epidemiological approaches. We illustrate this framework using the example of the transmission of Avian Influenza Viruses across wild bird/poultry interfaces in Africa and discuss a range of other examples that demonstrate the usefulness of our definition for other multi-host systems. Bridge hosts can be particularly important for understanding and managing infectious disease dynamics in multi-host systems at wildlife/domestic/human interfaces, including emerging infections.
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    Cultural ecosystem services and the avifauna of the Western Cape: a social-ecological systems investigation
    (2014) Heydinger, John Moore; Cumming, Graeme
    The ecosystem services concept has become inextricably linked to the economic valuation approach. Such an approach rests upon a triple incoherency, inadequately accounting for relationships between natural components, social and natural components, and within society itself. These incoherencies have distracted the ecosystem services concept away from its initial grounds: the reliance of humans upon the natural world. The faults of these three arenas are reviewed and found to be insuperable – ecosystem services must be re-imagined if they are to support positive conservation efforts. Such re-imagination here takes place within the framework of Social-ecological Systems (SES) theory. Founded upon the unifying concept of change, SES theory introduces a needed awareness of the dynamic interactions which characterize the process by which ecosystem services are realized by people. This introductory chapter sets the premise from which the rest of this thesis will operate: that the ecosystem services concept must account for the temporal dynamics of social-ecological interactions. Once an element of change becomes linked to ecosystem services only then can the concept may speak meaningfully to the co-constitution of the social and ecological arenas
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    Fynbos connectivity as a function of dispersal distance and the implications for bird conservation in the greater Cape Town area
    (2013) Kennedy, Kristen; Cumming, Graeme
    Connectivity is defined as the degree to which a landscape facilitates an organisms' movement. It is considered a vital element of landscape structure with key implications for metapopulation survival and ecological processes such as pollination. The connectivity of a landscape changes depending on an organisms' ability to move between patches of favourable habitat and this in turn is related to the dispersal ability of the organism. Connectivity thus changes with the scale at which the landscape is viewed; however the relationship between connectivity and dispersal ability is overlooked in many studies. This study looks at the connectivity of two types of fynbos: Highland fynbos (Thicket, Bushland, Bushclumps and High fynbos) which makes up 22.7%, and Lowland fynbos (Shrubland and Low Fynbos) which makes up 28% of the studied extent. These vegetation types are outlined by the National Land Cover Database (NLCD 2000) and analysed as a function of organism dispersal ability in the greater Cape Town area. It is shown that a relationship between dispersal ability and connectivity exists; however the relationship is not linear but sigmoidal with inflection points at 45% connectivity. This raises the question of a connectivity threshold in the Fynbos Biome. Characteristics of the landscape are assessed and it is shown that Fynbos vegetation in the greater Cape Town area is highly fragmented. Fragmentation and habitat loss decrease connectivity and are thus important factors in conservation. In order to simulate the effect of further fragmentation through habitat loss, patches of increasing size were removed and the results put into context for conservation of both the vegetation types and the dispersing organisms dependent on them. The importance of conserving patches of remnant vegetation in order to facilitate organism dispersal is highlighted by this study.