Browsing by Author "MacFadyen, Sandra"
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- ItemGenetic analysis shows low levels of hybridization between African wildcats (Felis silvestris lybica) and domestic cats (F. s. catus) in South Africa(John Wiley & Sons Ltd., 2015) Le Roux, Johannes J.; Foxcroft, Llewellyn C.; Herbst, Marna; MacFadyen, SandraHybridization between domestic and wild animals is a major concern for biodiversity conservation, and as habitats become increasingly fragmented, conserving biodiversity at all levels, including genetic, becomes increasingly important. Except for tropical forests and true deserts, African wildcats occur across the African continent; however, almost no work has been carried out to assess its genetic status and extent of hybridization with domestic cats. For example, in South Africa it has been argued that the long-term viability of maintaining pure wildcat populations lies in large protected areas only, isolated from human populations. Two of the largest protected areas in Africa, the Kgalagadi Transfrontier and Kruger National Parks, as well as the size of South Africa and range of landscape uses, provide a model situation to assess how habitat fragmentation and heterogeneity influences the genetic purity of African wildcats. Using population genetic and home range data, we examined the genetic purity of African wildcats and their suspected hybrids across South Africa, including areas within and outside of protected areas. Overall, we found African wildcat populations to be genetically relatively pure, but instances of hybridization and a significant relationship between the genetic distinctiveness (purity) of wildcats and human population pressure were evident. The genetically purest African wildcats were found in the Kgalagadi Transfrontier Park, while samples from around Kruger National Park showed cause for concern, especially combined with the substantial human population density along the park's boundary. While African wildcat populations in South Africa generally appear to be genetically pure, with low levels of hybridization, our genetic data do suggest that protected areas may play an important role in maintaining genetic purity by reducing the likelihood of contact with domestic cats. We suggest that approaches such as corridors between protected areas are unlikely to remain effective for wildcat conservation, as the proximity to human settlements around these areas is projected to increase the wild/domestic animal interface. Thus, large, isolated protected areas will become increasingly important for wildcat conservation and efforts need to be made to prevent introduction of domestic cats into these areas.
- ItemLinking long-term patterns of landscape heterogeneity to changing ecosystem processes in the Kruger National Park, South Africa(Stellenbosch : Stellenbosch University, 2018-12) MacFadyen, Sandra; Hui, Cang; Verburg, P. H.; Van Teeffelen, A. J. A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.ENGLISH ABSTRACT: Biodiversity loss is a global threat to ecosystem function and human well-being. Environmental heterogeneity is a recognised driver of biodiversity under a niche-based view of available species habitats. As such, an increase in environmental heterogeneity is expected to promote species coexistence, persistence and diversification. Loss of environmental heterogeneity is therefore considered proximal evidence of biodiversity loss. At a landscape scale, this heterogeneity is defined as the degree of difference between landscape elements and is often described as landscape heterogeneity. Patterns of landscape heterogeneity are generated and maintained by the physical landscape template or abiotic environment (e.g. topography, geology and climate), upon which complex adaptive interactions between landscape pattern (structure and composition) and ecological processes (function) occur. Landscape pattern can therefore be described as the self-organising expression of landscape function which varies not only across space but also through time. Accordingly, observable variations in landscape pattern are conjectured to signify divergence in landscape function. This thesis explores this relationship further within the Kruger National Park (Kruger): a large (~ 20,000 km2 ), longestablished (proclaimed 1898) protected area in South Africa’s semi-arid savanna. Results therefore describe landscape heterogeneity, in terms of the abiotic and biotic components (environmental drivers) that generate and maintain landscape pattern in Kruger, to inform strategic biodiversity planning. Chapter 1 introduces the reader to landscape heterogeneity and its relevance to protected area management and biodiversity conservation. Chapter 2 begins by isolating the effects of ‘stationary’ landscape properties on environmental heterogeneity through their relationship with Landsat spectral variance. Results show this relationship is sensitive to season and rainfall with the effects of dynamic ecosystem processes dominating many areas. Thereafter, Chapters 3 and 4 examine in more detail the nature of selected dynamic drivers in Kruger, namely rainfall and elephants. Results demonstrate the existence of longterm spatiotemporal changes in both rainfall and elephant density and distribution patterns in Kruger from 1985-2015. Together these results feed into chapter 5, where a Structural Equation Model (SEM) is used to investigate the causal structure of landscape heterogeneity with stable landscape properties, rainfall, herbivory and fire. Results are presented as path coefficients and long-term driver dominance maps showing the magnitude and direction of the different cause and effect relationships between heterogeneity, the physical landscape template, rainfall, herbivory and fire return interval. Finally the nature of the environmental-heterogeneity theory is operationalised in Chapter 6 using R, Shiny and Leaflet to provide an interactive web interface for protected area managers to explore heterogeneity differences in context with park specific research questions. Chapter 7 concludes the thesis with a brief synthesis of results in context with current literature and highlights future research opportunities and possible directions.
- ItemThe role of environmental factors in promoting and limiting biological invasions in South Africa(Springer, Cham., 2020) Wilson, John R.; Foxcroft, Llewellyn C.; Geerts, Sjirk; Hoffmann, M. Timm; MacFadyen, Sandra; Measey, John; Mills, Anthony; Richardson, David M.; Robertson, Mark P.; van Wilgen, Brian W.This chapter provides an overview of the researchers and research initiatives relevant to invasion science in South Africa over the past 130 years, profiling some of the more recent personalities, particularly those who are today regarded as international leaders in the field. A number of key points arise from this review. Since 1913, South Africa has been one of a few countries that have investigated and implemented alien plant biological control on a large scale, and is regarded as a leader in this field. South Africa was also prominent in the conceptualisation and execution of the international SCOPE project on the ecology of biological invasions in the 1980s, during which South African scientists established themselves as valuable contributors to the field. The development of invasion science benefitted from a deliberate strategy to promote multi-organisational, interdisciplinary research in the 1980s. Since 1995, the Working for Water programme has provided funding for research and a host of practical questions that required research solutions. Finally, the establishment of a national centre of excellence with a focus on biological invasions has made a considerable contribution to building human capacity in the field, resulting in advances in all aspects of invasion science—primarily in terms of biology and ecology, but also in history, sociology, economics and management. South Africa has punched well above its weight in developing the field of invasion science, possibly because of the remarkable biodiversity that provided a rich template on which to carry out research, and a small, well-connected research community that was encouraged to operate in a collaborative manner.
- ItemSpatiotemporal distribution dynamics of elephants in response to density, rainfall, rivers and fire in Kruger National Park, South Africa(Wiley, 2019) MacFadyen, Sandra; Hui, Cang; Verburg, Peter H.; Van Teeffelen, Astrid J. A.Aim: African elephants are ecosystem engineers. As such, their long‐term patterns of distribution and abundance (i.e., space‐use intensity) will influence ecosystem structure and function. We elucidate these patterns for bull versus herd groups, by analysing the spatiotemporal dynamics of an increasing elephant population in relation to key ecological drivers: rainfall, distance to major rivers and time since last fire. Significant changes to the long‐term patterns of elephant density and group‐type probabilities are identified and explained. Location: Kruger National Park, South Africa. Methods: Using almost three decades of census records (1985–2012), we applied Multiple Point Process Models to assess the influence of rainfall, rivers and fire in shaping elephant space‐use. Significant changes to the long‐term patterns of elephant density and group type were also identified using kernel density estimates and the spatially varying probability of encountering either bull or herd group. Results: Bull and herd groups are no longer clearly segregated as available empty space becomes more limited. Bull and herd groups have dichotomous resource selection functions, in that bulls concentrate in areas receiving lower rainfall but more frequent fires while herds concentrate in higher rainfall areas experiencing less frequent fires. Both bull and herd groups concentrate closer to major rivers, emphasizing rivers as important spatial drivers. Overall, densities increased most significantly closer to rivers and in areas experiencing fewer fires. Fire was also a strong agent of group‐type change, as the probability of finding bulls, contrary to herds, significantly increased as fire return periods shortened. Main conclusions: Elephant distribution and abundance patterns have homogenized in response to increased space limitations, with group‐specific, fire‐driven distribution patterns emerging overtime. Results herein should be used to help manage elephant space‐use through the establishment of possible refuge areas and the development of more empirical research into elephant impacts in future.