Browsing by Subject "disturbance"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    Population Dynamics, Disturbance, and Pattern Evolution: Identifying the Fundamental Scales of Organization in a Model Ecosystem
    (1998) Wiegand, Thorsten; Moloney, Kirk A; MILTON, SUZANNE J
    ABSTRACT We used auto‐ and cross‐correlation analysis and Ripley's K ‐function analysis to analyze spatiotemporal pattern evolution in a spatially explicit simulation model of a semiarid shrubland (Karoo, South Africa) and to determine the impact of small‐scale disturbances on system dynamics. Without disturnities bance, local dynamics were driven by a pattern of cyclic succession, where ‘colonizer’ and ‘successor’ species alternately replaced each other. This results in a strong pattern of negative correlation in the temporal distribution of colonizer and successor species. As disturbance rates were increased, the relationship shifted from being negatively correlated in time to being positively correlated—the dynamics became decoupled from the ecologically driven cyclic succession and were increasingly influenced by abiotic factors (e.g., rainfall events). Further analysis of the spatial relationships among colonizer and successor species showed that, without disturbance, periods of attraction and repulsion between colonizer and successor species alternate cyclically at intermediate spatial scales. This was due to the spatial ‘memory’ embedded in the system through the process of cyclic succession. With the addition of disturbance, this pattern breaks down, although there is some indication of increasing ecological organization at broader spatial scales. We suggest that many of the insights that can be gained through spatially explicit models will only be obtained through a direct analysis of the spatial patterns produced.
  • Thumbnail Image
    Item
    Restricted
    The management of Avian Cholera Pasteurella multicida outbreaks on Dyer Island, South Africa, 2002-2005
    (2007) Waller, L J; Underhill, L G
    In 2002 there was a widespread epizootic involving seabirds on five of the offshore islands of the Western Cape, South Africa. Since then, avian cholera Pasteurella multocida outbreaks have been occurring annually on one of these islands, Dyer Island. This paper reports on the three subsequent summers, 2003/04, 2004/05 and 2005/06, during which further avian cholera outbreaks were recorded. It focuses on the outbreak in 2004/05, which was the largest in extent and the most closely monitored. The mortalities during 2005/06 were not as extensive as expected. The management measures used to bring these outbreaks under control are described. Removal of all the carcasses from the entire island in one day is important in reducing mortality. Management intervention is required to reduce the negative impacts of disturbance due to kelp gull Lasus dominicanus predation on other breeding seabirds, primarily the African penguin Spheniscus demersus, during the carcass collection process.