Browsing by Author "Peta, Samuel Tebogo Posie"

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    Trophic interactions of the Guttural Toad (Sclerophrys gutturalis, Power 1927) along an invasion gradient
    (Stellenbosch : Stellenbosch University, 2022-04) Peta, Samuel Tebogo Posie; Measey, John; Baxter-Gilbert, James; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Invasive amphibians have caused widespread negative ecological and socio- economic impacts globally, yet most of the research investigating this topic is focused on a small handful of species. The Guttural Toad (Sclerophrys gutturalis) is one such understudied species that has a long invasion history on Mauritius (~100 years) and Reunion (~95 years), and a recent domestic invasion in Cape Town (~22 years). It is a successful invasive species and has been implicated in the imperilment of native taxa, however, little is known about their specific diet or how their feeding habits have facilitated their invasion success. In Mauritius, S. gutturalis has been suggested to be a contributing factor to declines of several species of endemic invertebrates, while their invasion in Cape Town has raised concerns about the potential for congeneric competition with the IUCN endangered Western Leopard Toad (Sclerophrys pantherina). The overarching goal of this thesis was to examine the diets, feeding habits, and trophic position of S. gutturalis along its invasion route from native-natural to native-urban (KwaZulu-Natal), to invasive- urban (Cape Town and Mauritius), and invasive-natural populations (Mauritius). Specifically, I undertook a comprehensive investigation of their dietary niche breadth, diet composition, and prey preferences using stomach content analysis. Moreover, I complimented stomach content analysis with stable isotope analysis to examine the toad’s trophic position, isotopic niche breadth, and competitive interaction with S. pantherina. Stomach content data demonstrated that S. gutturalis is a highly adaptable and flexible feeder, with a diet typically comprising of terrestrial invertebrates and a limited proportion of small-bodied vertebrates. Native-natural populations contracted their dietary niche breadth as they transitioned into native-urban habitats due to reduced prey diversity in urban habitats. The expansion of dietary niche breadth in invasive-natural populations may be linked with a shift towards diurnal feeding activity, allowing for increased access to resources within their invaded range. Across populations prey preference varied, however, all populations preferred invasive prey – an indication that the presence of other invasive taxa may promote the toad’s invasion success. Compared to rural populations, urban populations prefer ingesting insects. This is indicative of the influence of garden plants and artificial lighting that help centralize food sources, as well as human activities that may further boost S. gutturalis invasions. Isotopic data demonstrated that, on average, invasive populations experienced a drop in trophic position. However, urban populations typically had elevated trophic positions – an indication of consuming nitrogen-rich prey that may be anthropogenically subsidised within urban spaces. The expansion and contraction of isotopic niche breadth reflected varying prey availability and isotopic baselines. The broad isotopic niche breadth in native populations indicated consumption of isotopically distinct prey. The moderate isotopic niche overlap between S. gutturalis and S. pantherina demonstrated the potential for competitive interactions, but the extent of this overlap varies greatly between these species. This research provides valuable dietary information that generates insight into how these toads have adapted to both urban and invaded habitats. This work contributes to both our knowledge of native S. gutturalis in southern Africa and informs future conservation actions and the management of invasive populations.