Browsing by Author "Vorster, Carlien"

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    Distribution and bait preference of the Argentine ant in natural vegetation
    (Stellenbosch : Stellenbosch University, 2011-12) Vorster, Carlien; McGeoch, Melodie A.; Prozesky, Heidi E.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Since its introduction in 1898 into South Africa, the Argentine ant, Linepithema humile [Mayr 1868 (Hymenoptera: Formicidae)], has invaded human-occupied areas (i.e. urban and agricultural areas) and natural areas characterised by few, if any, anthropogenic disturbances. However, compared to other countries in which the Argentine ant has been recorded, and until the past few decades, very little research had been done on this invasive ant in South Africa. Consequently, several issues concerning its ecological and social effects are still under-researched. The first of these issues concerns the lack of knowledge about the distribution of the Argentine ant in the natural areas, particularly the protected areas (PAs), of South Africa. In order to determine how many PAs are occupied by this invasive ant, a study was conducted in the Western Cape Province (WCP). It was found that, of the 614 PAs documented for WCP, ten have a known presence and nine known absence records of the Argentine ant. The remainder of the PAs have no known occupancy records for this ant. A second issue concerns the seasonal bait preference of the Argentine ant in a fynbos habitat. Six bait treatments (two carbohydrate and protein baits, a mixture of the carbohydrate and protein treatments, and a control) were applied in a fynbos habitat across a sampling grid in four different Latin Square designs, i.e. once for every season. Based on these experiments, it was determined that the Argentine ant prefers the mixture of carbohydrate and protein treatments, and that this preference does not change according to season. Furthermore, previous studies conducted in Jonkershoek Nature Reserve [JNR (in WCP)] determined the existence of a distribution boundary of Argentine ants in an area known as Swartboschkloof. Therefore, the third issue concerned the exact location of the distribution boundary and possible reasons for its establishment. This distribution boundary of the Argentine ant was found to be present 450 m from Swartboschkloof hiking trail. A combination of several explanatory variables may contribute to the maintenance of this boundary, i.e. a change in the horizontal and vertical vegetation distribution, as well as in the slope and aspect across the distribution boundary. With these explanatory variables, the increasing presence of an indigenous ant species, Anoplolepis custodiens, from this boundary may also have contributed to the distribution boundary. In addition, the short-term effect of a fire that swept through this area was also assessed, which revealed that Argentine ants are severely negatively affected by fire (at least over the short-term), i.e. their abundance decreased considerably after the fire and their local distribution range contracted. The final issue concerns the public perceptions of invasive alien species (IAS) in general and the Argentine ant specifically, at JNR. This study revealed that the majority of visitors to JNR were aware of the presence of IAS in South Africa and in its PAs, while very few visitors knew about the Argentine ant. This study also revealed that future research concerning South Africans perceptions of IAS might play a strong contributing role in conservation.
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    A practical tool for evaluating freshwater health and biodiversity across Africa
    (Stellenbosch : Stellenbosch University, 2018-12) Vorster, Carlien; Samways, Michael J.; Simaika, John Pascal Simaika; Dijkstra, Klaas-Douwe B.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The diverse African freshwater ecosystems are being increasingly impacted by human activities. Biomonitoring tools are needed to address the level of impacts and success of mitigation. Here a biomonitoring tool, using an effective indicator group (Dragonflies: Odonata), is developed at the African continental scale, while using the South African Dragonfly Biotic Index (DBI) as a starting point. The DBI can be applied to both still and running waters, and is based on three sub-indices (geographical distribution, threat status, and habitat sensitivity) of each dragonfly species. Data on dragonflies has been collated through international effort into the Odonata Database of Africa, used here to develop a new index, the African Dragonfly Biotic Index (ADBI). As with the DBI, the ADBI uses the same first two sub-indices (distribution and threat status), but replaces habitat sensitivity with a species vulnerability sub-index. This is more appropriate for the continental level in view of the quality of data available. Careful data interrogation led to final selection of 604 African dragonfly species for development of the ADBI. While the South African DBI scores were calculated at a national level, the ADBI scores were determined at a continental scale, which necessitated some changes in the calculations of the ADBI scores. To determine exactly how the ADBI deviated from the DBI, these two biotic indices were compared using just the South African dragonfly species as a data sub-set. There was a strong correlation between the Red List threat status sub-index and final scores of the ADBI and DBI, while geographical distribution sub-index scores of the ADBI and DBI were only moderately correlated. The sub-index that contributed most to the deviation of the ADBI from the DBI, was the ADBI species vulnerability sub-index. Although appropriate for a continental scale assessment, the ADBI has shortcomings for national level assessments, where conservation policy and management takes place. This meant that the ADBI had to be translated for specific use in the different countries so as to develop national biomonitoring schemes (i.e. a national DBI). However, as the spatial database created for Africa’s dragonflies varies in quality and quantity, the countries are at various levels of national DBI development. Countries were categorized on their potential to develop national DBIs by determining the value of data coverage of each country. Of the 48 African countries (excluding South Africa, which already has a national DBI), there are 12 that are close to being able to implement national DBIs, while another 12 have insufficient data and are not currently able to implement national DBIs. The other 24 countries require much more basic data to instigate national DBIs. Bioassessments of freshwaters takes place at two levels: 1) within political borders, and 2) in biogeographical regions. However, what is expedient at the national level often does not match biogeographical categories (e.g. ecoregions). Hence, the continental-scale ADBI was investigated according to Africa’s terrestrial and freshwater ecoregions. There were no significant differences between assessments using terrestrial vs. freshwater ecoregions, although using terrestrial ecoregions gives a finer interpretation of freshwater condition.