South Africa
South Africa

Time filter

Source Type

le Roux P.C.,Stellenbosch University | McGeoch M.A.,Stellenbosch University | McGeoch M.A.,Cape Research Center
Oecologia | Year: 2010

The stress-gradient hypothesis (SGH) predicts that the community-wide prevalence of positive interactions, relative to negative interactions, is greater under more severe environmental conditions. Because the frequency of positive and negative interactions within a community is the aggregate of multiple pair-wise interactions, one approach to testing the SGH is to examine how pair-wise interactions vary along severity gradients. While the SGH suggests that the net outcome of an interaction should monotonically become more positive with increasing environmental severity, recent studies have suggested that the severity-interaction relationship (SIR) may rather be unimodal. We tested which of the proposed shapes of the SIR best fits the variation in the interaction between two species along two types of severity gradients on sub-Antarctic Marion Island. This was done by comparing the performance of the grass Agrostis magellanica in the presence and absence of the cushion plant Azorella selago, along both species' entire altitudinal ranges (transects spanning 4-8 km), and along a shorter (transect = 0.4 km) wind exposure gradient. Along the altitudinal transects the relative intensity, but not the absolute intensity or the importance, of the Azorella selago-Agrostis magellanica interaction increased with altitude, consistently forming a plateau-shaped SIR with a positive asymptote. Thus, while the performance of Agrostis magellanica was negatively affected by Azorella selago at low altitudes, the grass benefited from growing on the cushion plant under greater environmental severity. Along the wind exposure gradient the intensity of the interaction also became more positive with increasing environmental severity for most performance measures. This suggests that the switch from a net negative to a net positive interaction can occur across both short and long distances. Therefore, this study provides strong evidence for a plateau-shaped SIR, and confirms that the SIR is unimodal along the particular non-resource severity gradients of this study. © Springer-Verlag 2009.


Born C.,Stellenbosch University | Le Roux P.C.,Stellenbosch University | Le Roux P.C.,University of Helsinki | Spohr C.,Stellenbosch University | And 4 more authors.
Molecular Ecology | Year: 2012

Climatic conditions and landscape features often strongly affect species' local distribution patterns, dispersal, reproduction and survival and may therefore have considerable impacts on species' fine-scale spatial genetic structure (SGS). In this study, we demonstrate the efficacy of combining fine-scale SGS analyses with isotropic and anisotropic spatial autocorrelation techniques to infer the impact of wind patterns on plant dispersal processes. We genotyped 1304 Azorella selago (Apiaceae) specimens, a wind-pollinated and wind-dispersed plant, from four populations distributed across sub-Antarctic Marion Island. SGS was variable with Sp values ranging from 0.001 to 0.014, suggesting notable variability in dispersal distance and wind velocities between sites. Nonetheless, the data supported previous hypotheses of a strong NW-SE gradient in wind strength across the island. Anisotropic autocorrelation analyses further suggested that dispersal is strongly directional, but varying between sites depending on the local prevailing winds. Despite the high frequency of gale-force winds on Marion Island, gene dispersal distance estimates (σ) were surprisingly low (<10 m), most probably because of a low pollen dispersal efficiency. An SGS approach in association with isotropic and anisotropic analyses provides a powerful means to assess the relative influence of abiotic factors on dispersal and allow inferences that would not be possible without this combined approach. © 2011 Blackwell Publishing Ltd.


Roets F.,Stellenbosch University | Pryke J.S.,Stellenbosch University | McGeoch M.A.,Cape Research Center
Journal of Insect Conservation | Year: 2013

There is often a lack of basic ecological data needed to implement effective conservation management programmes for endangered arthropods. This is particularly true for the highly localized and rare Colophon, a genus of beetles of which all members are narrow range endemics of conservation concern. The genus is confined to the highest mountain peaks in the Cape Floristic Region of South Africa and each of the 17 known species is endemic to a particular mountain or range. We investigated the influence of selected abiotic variables on adult Colophon westwoodi activity in Table Mountain National Park, South Africa, which will aid the development of an effective monitoring programme. Weekly surveys conducted on Table Mountain showed that adult numbers peaked during early summer. Adults were active at dusk on clear days, although earlier when misty. Unexpectedly, relative humidity and air temperature had no significant effect on Colophon abundance, while illuminance was the most important predictor. Contrary to general consensus, C. westwoodi activity is not strictly crepuscular but also appears nocturnal. Thus, Colophon monitoring programmes need to be conducted in early summer after sunset and monitoring can continue later than previously assumed. Little is still known about C. westwoodi population size, area of occupancy, general behaviour and the impact tourists have on it, or indeed why the genus is restricted to mountain tops. Therefore this research is important for the design of monitoring protocols for this flagship species, while at the same time directing future research. © 2012 Springer Science+Business Media B.V.


Veldtman R.,Stellenbosch University | Chown S.L.,Stellenbosch University | McGeoch M.A.,Stellenbosch University | McGeoch M.A.,Cape Research Center
Diversity and Distributions | Year: 2010

Aim Invasive species distribution and abundance data are essential for management decisions on mitigating impacts but is seldom available. Here, we use scale-area curves to assess the distribution, abundance and consequent management implications of an invasive plant (Acacia longifolia) within selected occupancy grid cells, spread across regional ranges and representing the full national extent. We determine whether occupancy patterns are explained by climatic suitability or range structure and identify areas where A. longifolia can still be regarded as an important invasive based on contiguous occupancy. Location South Africa including the Fynbos, Thicket, Savanna and Grassland biomes. Methods The quarter degree occupancy of A. longifolia was used to select core, edge, and climatically unsuitable grid cells within different regions of the national range. Cells were surveyed across a linear resolution from 25 km to 2.5 m allowing the first multi-scales description of an invasive species' space-filling properties. Patterns from grid cells in turn were viewed regionally to describe regional variation in spatial structure. Results In regions with contiguous areas of favourable habitat, scale-area curves indicated greater occupancy in core than edge areas, whereas patterns were reversed when suitable areas were more fragmented. Also, at times climatically suitable areas were unoccupied, while unsuitable areas were occupied. Within cells, occupancy was well explained by the presence of fynbos vegetation types, while nationally, contiguous occupancy was almost exclusive to the Fynbos Biome. Main conclusions Scale-area curves can advance the understanding of biological invasions and invasive plant distributions. Here, we detected potential areas of invasive concern, plus differences in abundance and distribution patterns, and associated correlates, at landscape and national scales. As there was no general relationship between range position or climatic suitability and A. longifolia's spatial structure, we propose habitat suitability as an alternative explanation which, in turn, suggests limited range expansion potential. © 2010 Blackwell Publishing Ltd.


McGeoch M.A.,Cape Research Center | McGeoch M.A.,Stellenbosch University | Spear D.,Stellenbosch University | Kleynhans E.J.,Stellenbosch University | Marais E.,Stellenbosch University
Ecological Applications | Year: 2012

Lists of invasive alien species (IAS) are essential for preventing, controlling, and reporting on the state of biological invasions. However, these lists suffer from a range of errors, with serious consequences for their use in science, policy, and management. Here we (1) collated and classified errors in IAS listing using a taxonomy of uncertainty; and (2) estimated the size of these errors using data from a completed listing exercise, with the purpose of better understanding, communicating, and dealing with them. Ten errors were identified. Most result from a lack of knowledge or measurement error (epistemic uncertainty), although two were a result of context dependence and vagueness (linguistic uncertainty). Estimates of the size of the effects of these errors were substantial in a number of cases and unknown in others. Most errors, and those with the largest estimated effect, result in underestimates of IAS numbers. However, there are a number of errors where the size and direction of the effect remains poorly understood. The effect of differences in opinion between specialists is potentially large, particularly for data-poor taxa and regions, and does not have a clearly directional or consistent effect on the size and composition of IAS lists. Five tactics emerged as important for reducing uncertainty in IAS lists, and while uncertainty will never be removed entirely, these approaches will significantly improve the transparency, repeatability, and comparability of IAS lists. Understanding the errors and uncertainties that occur during the process of listing invasive species, as well as the potential size and nature of their effects on IAS lists, is key to improving the value of these lists for governments, management agencies, and conservationists. Such understanding is increasingly important given positive trends in biological invasion and the associated risks to biodiversity and biosecurity. © 2012 by the Ecological Society of America.


van Wilgen N.J.,Stellenbosch University | van Wilgen N.J.,Cape Research Center | Richardson D.M.,Stellenbosch University
Conservation Biology | Year: 2012

We developed a method to predict the potential of non-native reptiles and amphibians (herpetofauna) to establish populations. This method may inform efforts to prevent the introduction of invasive non-native species. We used boosted regression trees to determine whether nine variables influence establishment success of introduced herpetofauna in California and Florida. We used an independent data set to assess model performance. Propagule pressure was the variable most strongly associated with establishment success. Species with short juvenile periods and species with phylogenetically more distant relatives in regional biotas were more likely to establish than species that start breeding later and those that have close relatives. Average climate match (the similarity of climate between native and non-native range) and life form were also important. Frogs and lizards were the taxonomic groups most likely to establish, whereas a much lower proportion of snakes and turtles established. We used results from our best model to compile a spreadsheet-based model for easy use and interpretation. Probability scores obtained from the spreadsheet model were strongly correlated with establishment success as were probabilities predicted for independent data by the boosted regression tree model. However, the error rate for predictions made with independent data was much higher than with cross validation using training data. This difference in predictive power does not preclude use of the model to assess the probability of establishment of herpetofauna because (1) the independent data had no information for two variables (meaning the full predictive capacity of the model could not be realized) and (2) the model structure is consistent with the recent literature on the primary determinants of establishment success for herpetofauna. It may still be difficult to predict the establishment probability of poorly studied taxa, but it is clear that non-native species (especially lizards and frogs) that mature early and come from environments similar to that of the introduction region have the highest probability of establishment. © 2012 Society for Conservation Biology.


Swemmer L.,Scientific Services South African National Parks | Grant R.,Scientific Services South African National Parks | Annecke W.,Cape Research Center | Freitag-Ronaldson S.,Scientific Services South African National Parks
Society and Natural Resources | Year: 2015

More examples of positive and negative outcomes of community-based conservation initiatives aimed at benefit sharing are surfacing globally, and there is increasing interest in who wins and who loses at multiple scales. However, the term “benefit sharing” is not well defined in the context of protected areas, hindering the effective implementation thereof. We define benefit sharing as the process of making informed and fair trade-offs between social, economic, and ecological costs and benefits within and between stakeholder groups, and between stakeholders and the natural environment. We explore identifying appropriate benefits in certain contexts and monitoring benefit sharing initiatives using relevant qualitative and quantitative indicators. Finally, we use an illustrative case study of mopane worm harvesting from the Kruger National Park in South Africa to explore how benefit sharing as defined in the article can be implemented using a strategic adaptive management approach during the planning, assessment, and reporting phases. © 2015, Taylor & Francis Group, LLC.


Masubelele M.L.,Cape Research Center | Hoffman M.T.,University of Cape Town | Bond W.J.,South African Environmental Observation Network
Journal of Vegetation Science | Year: 2015

Questions: How has the vegetation of the major biomes (Grassland, Nama-karoo, Albany Thicket, Azonal) of southeastern South Africa changed over the course of the 20th century? How do changes in climate and land-use drivers relate to long-term changes in vegetation? What are the implications of these findings for land degradation hypotheses and future climate change projections for the region? Location: The biogeographically complex semi-arid, Karoo Midlands region of the southeastern part of South Africa. Methods: We re-photographed 65 historical landscape photographs, the majority of which dated from 1950 to 1970, to measure long-term changes in the cover of grasses, dwarf shrubs, tall shrubs and alien plants. The cover of each growth form as well as total vegetation cover was estimated from matched photograph pairs with the aid of detailed cover estimates recorded in the field. The change in cover was relativized between sites by dividing the difference in cover between the two time steps by the number of years between photographs, expressed as the percentage change in cover per decade. Significant changes in mean annual rainfall and the standardized precipitation index (SPI) from 27 climate stations were assessed using a Mann-Kendall test for trend. This non-parametric test was also used to assess the significance of long-term trends in the number of cattle, sheep and goats in each of the biomes over the period 1911-1996. Results: Grass cover and total vegetation cover had increased by between 1.0% to 4.5% per decade and 2.0% to 4.5% per decade, respectively, in all biomes investigated. In contrast, the cover of dwarf shrubs had decreased significantly by between 0.25% and 3.0% per decade, although not significantly so in the Nama-karoo biome. The change in tall shrub cover varied between different biomes but had generally increased in the study area. Alien plants were absent in the historical photographs and had increased significantly but only in Azonal habitats, where increases of 1.5% per decade were recorded. For the majority of climate stations no significant trend in mean annual rainfall and SPI values was recorded, while stocking rate had declined significantly in all biomes by between 36% and 48% from 1911 to 1996. Conclusions: The findings support the hypothesis that vegetation cover and condition has improved in the semi-arid regions of South Africa. These findings are discussed in light of future projections for the region. © 2015 International Association for Vegetation Science.


Rebelo T.G.,South African National Biodiversity Institute | Freitag S.,Kruger National Park | Cheney C.,Table Mountain National Park | McGeoch M.A.,Cape Research Center
Koedoe | Year: 2011

Conservation requires that species are monitored to ensure the persistence of species and ecosystem processes. In areas with large numbers of threatened species, this can be a major challenge. Here we explore prioritising species of special concern on the Cape Peninsula, South Africa, conserved primarily in the Table Mountain National Park. With 307 terrestrial plant and animal species listed as threatened on the IUCN Red List (plus 208 as non-least concern) and 332 endemic to the Peninsula, it is impossible to monitor and manage all species with current resources. At a workshop of conservation managers and ecosystem and taxonomical specialists, 14 variables were incorporated into a simple scoring scheme to develop a priority listing of these species. Despite care to ensure that variables were independent, there was strong autocorrelation amongst biotic versus management variables. There was concern that biotic variables would be masked by management criteria, but this was not the case. We propose that monitoring should focus on as many top-scoring species as resources allow (including volunteers) and that setting a cut-off value for delimiting sensitive species should be eschewed. A major challenge is that many species are typical of lowland ecosystems, which are poorly represented in the national park. Although priority species for monitoring have been identified, this will need to be tempered with the monitoring costs and logistics of implementing the programme. Conservation implications: Owing to the large number of threatened and endemic species in the Cape Peninsula, it is impossible to monitor all species with current resources. Management must focus on ecosystem maintenance as species-focused management will inevitably result in conflict with other threatened species. Monitoring should focus on as many top-scoring species as resources allow. The costs and logistics of a monitoring programme still need to be worked out. © 2011.


Annecke W.,Cape Research Center | Masubelele M.,Cape Research Center
Conservation and Society | Year: 2016

This paper is addressed to academics, conservation agencies and governments primarily in developing countries, faced with the need to protect species from poaching by global syndicates or local groups that threaten the survival of species. The argument of this paper is that while military intervention may provide short to medium terms gains, these have to be weighed against the likely medium to long term financial and socio-economic costs of military activity on people, including the military themselves, and conservation. These costs are likely to be significant and may even threaten the sustainability of conservation areas. While the analysis is developed in relation to the military intervention to inhibit rhino poaching in the Kruger National Park, South Africa, the literature review reveals that similar challenges occur internationally and the South African case study may be applicable to a wide range of anti-poaching conservation efforts and military options throughout the developing world. A multi-pronged approach, where all components are strongly implemented, is necessary to combat poaching. Copyright: © Annecke and Masubelele 2016.

Loading Cape Research Center collaborators
Loading Cape Research Center collaborators