Browsing by Author "Geldenhuys, Frieda"
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- ItemUsing species distribution models for spatial conservation planning of African Penguins(Stellenbosch : Stellenbosch University, 2018-03) Geldenhuys, Frieda; Hui, Cang; Nieuwoudt, Martin; Stellenbosch University. Faculty of Science. Dept. of Mathematical Sciences.ENGLISH ABSTRACT: The African penguin Spheniscus demersus inhabits the south-western coast of Africa, between Namibia and Algoa Bay, near Port Elizabeth, South Africa, with the largest colony consisting of about 44% of South Africa’s penguins, found on St. Croix Island. The penguin population is currently at about 2% of the level it was in the 1900s, and is still continuing its strong downward population trajectory. The decrease in the population of African penguins is an early warning indicator of environmental threats, thus studying the factors that affect it is important. The African penguin has been declared Endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Due to their population decrease, immediate conservation action is required to prevent this species’ extinction. An understanding of the dynamics and causes of this decrease, is thus of critical importance. The aim of this study is to better understand the effects of drivers of change on the African penguin colonies. The establishment of a sustainable management plan for the African penguin species, by consolidating different approaches, has been investigated. Studies indicate that the drivers of change in the population size include climate change, parasites, pollution (oiling), disease, lack of food resources, predation risk and habitat interference. A large component of this is the anthropogenic impact, especially with human population expansion. As a result of this, ecological traps or scenarios in which organisms settle in habitats of poor quality, due to rapid environmental change, emerge. For example, high plankton populations could indicate high fish populations in an area, although this indicator may be incorrect if the fish have been harvested. This area may thus be an ecological trap for penguins. It is important, for conservation purposes, to be able to identify the ecological traps and differentiate them from sinks or low quality habitats that, on their own, would not have the resources to support a population. The information required to assess the consequences of ecological traps was investigated. Of particular concern are the shifting distributions of forage fish, which may result in a spatial mismatch between the main penguin breeding colonies and their preferred prey. The foraging range of penguins during the breeding season is particularly limited, as foraging trips typically last less than one day. Spatial closures, in the form of marine protected areas, as well as those that permanently prohibit fishing, termed no-take reserves, can be used to manage the fishing effort, and in complementing alternative controls such as quota management. Species Distribution Models (SDMs) have been established in response to these challenges. These are predictive, conceptual models of the abiotic (e.g. physical barriers, climate, lack of resources) and biotic (e.g. competition, predators, parasites) factors influencing the role of habitat suitability in affecting the distribution of species in terms of space, time and scale. To begin with, the demography of the African penguin has been investigated. Thereafter, the modelling method has been described. R statistical programming language has been used to create the SDMs, from the colony location inputs and corresponding environmental data. The Maximum Entropy algorithm used 5 environmental, non-correlated variables and presence-only records (from 33 colonies). The relative contributions of environmental variables, which are ecologically relevant to the species habitat suitability, indicate that sea surface temperature is the largest contributing factor, with 72.4% for annual, 53.2% for summer and 46.9% for winter factors. The second largest contributor for all seasons is mean land temperature. The outputs of this study act as a baseline assessment. Possible areas to relocate or establish African penguin colonies, based on their prey availability, include the old De Hoop colony (which went extinct in 2006) and a site near Plettenberg Bay (which would be a completely new site), according to BirdLife. Camera traps for checking predators, have been in place since November 2016. From this study, it is clear that ongoing research is necessary, mainly due to the shifting distribution of prey, which is caused by climate change and overfishing, in order to model the African penguin colonies. Keywords: African penguins, Conservation, Species Distribution Models, Suitability Maps