Browsing by Author "De Villiers, Andre"

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    Are invasive populations characterized by a broader diet than native populations?
    (PeerJ, 2017) Courant, Julien; Vogt, Solveig; Marques, Raquel; Measey, John; Secondi, Jean; Rebelo, Rui; De Villiers, Andre; Ihlow, Flora; De Busschere, Charlotte; Backeljau, Thierry; Rodder, Dennis; Herrel, Anthony
    Background. Invasive species are among the most significant threats to biodiversity. The diet of invasive animal populations is a crucial factor that must be considered in the context of biological invasions. A broad dietary spectrum is a frequently cited characteristic of invasive species, allowing them to thrive in a wide range of environments. Therefore, empirical studies comparing diet in invasive and native populations are necessary to understand dietary requirements, dietary flexibility, and the associated impacts of invasive species. Methods. In this study, we compared the diet of populations of the African clawed frog, Xenopus laevis in its native range, with several areas where it has become invasive. Each prey category detected in stomach contents was assigned to an ecological category, allowing a comparison of the diversity of ecological traits among the prey items in the diet of native and introduced populations. The comparison of diets was also performed using evenness as a niche breadth index on all sampled populations, and electivity as a prey selection index for three out of the six sampled populations. Results. Our results showed that diet breadth could be either narrow or broad in invasive populations. According to diet and prey availability, zooplankton was strongly preferred in most cases. In lotic environments, zooplankton was replaced by benthic preys, such as ephemeropteran larvae. Discussion. The relative proportions of prey with different ecological traits, and dietary variability within and between areas of occurrence, suggest that X. laevis is a generalist predator in both native and invasive populations. Shifts in the realized trophic niche are observed, and appear related to resource availability. Xenopus laevis may strongly impact aquatic ecosystems because of its near complete aquatic lifestyle and its significant consumption of key taxa for the trophic relationships in ponds.
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    Food ingredient extracts of Cyclopia subternata (Honeybush) : variation in phenolic composition and antioxidant capacity
    (MDPI, 2012) De Beer, Dalene; Schulze, Alexandra E.; Joubert, Elizabeth; De Villiers, Andre; Malherbe, Christiaan J.; Stander, Maria A.
    Cyclopia subternata plants are traditionally used for the production of the South African herbal tea, honeybush, and recently as aqueous extracts for the food industry. A C. subternata aqueous extract and mangiferin (a major constituent) are known to have anti-diabetic properties. Variation in phenolic composition and antioxidant capacity is expected due to cultivation largely from seedlings, having implications for extract standardization and quality control. Aqueous extracts from 64 seedlings of the same age, cultivated under the same environmental conditions, were analyzed for individual compound content, total polyphenol (TP) content and total antioxidant capacity (TAC) in a number of assays. An HPLC method was developed and validated to allow quantification of xanthones (mangiferin, isomangiferin), flavanones (hesperidin, eriocitrin), a flavone (scolymoside), a benzophenone (iriflophenone-3-C-β-glucoside) and dihydrochalcones (phloretin-3',5'-di-C-β-glucoside, 3-hydroxyphloretin-3',5'-di-C-hexoside). Additional compounds were tentatively identified using mass spectrometric detection, with the presence of the 3-hydroxyphloretin-glycoside, an iriflophenone-di-O,C-hexoside, an eriodictyol-di-C-hexoside and vicenin-2 being demonstrated for the first time. Variability of the individual phenolic compound contents was generally higher than that of the TP content and TAC values. Among the phenolic compounds, scolymoside, hesperidin and iriflophenone-3-C-β-glucoside contents were the most variable. A combination of the measured parameters could be useful in product standardization by providing a basis for specifying minimum levels.
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    Die verhouding, Christendom en tradisionele religie by die ontwikkelde Sjona-jeug
    (Stellenbosch : Stellenbosch University, 1973-12) De Villiers, Andre; Van der Merwe, W. J.; Smith, N. J.; Stellenbosch University. Faculty of Theology. Dept. of Practical Theology and Missiology.
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