Competition and feeding ecology in two sympatric Xenopus species (Anura: Pipidae)

Abstract

The widespread African clawed frog (Xenopus laevis) occurs in sympatry with the IUCN Endangered Cape platanna (Xenopus gilli) throughout its entire range in the south-western Cape, South Africa. In order to investigate aspects of the interspecific competition between populations of X. laevis and X. gilli, an assessment of their niche differentiation was conducted through a comprehensive study on food composition and trophic niche structure at two study sites: the Cape of Good Hope (CoGH) and Kleinmond. A total of 399 stomach contents of X. laevis (n = 183) and X. gilli (n = 216) were obtained together with samples of available prey to determine food preferences using the Electivity index (E*), the Simpson’s index of diversity (1 − D), the Shannon index (H′), and the Pianka index (Ojk). Xenopus gilli diet was more diverse than X. laevis, particularly in Kleimond where the Shannon index was nearly double. Both species were found to consume large amounts of tadpoles belonging to different amphibian species, including congeners, with an overall higher incidence of anurophagy than previously recorded. However, X. laevis also feeds on adult X. gilli, thus representing a direct threat for the latter. While trophic niche overlap was 0.5 for the CoGH, it was almost 1 in Kleinmond, suggesting both species utilise highly congruent trophic niches. Further, subdividing the dataset into three size classes revealed overlap to be higher in small frogs in both study sites. Our study underlines the importance of actively controlling X. laevis at sites with X. gilli in order to limit competition and predation, which is vital for conservation of the south-western Cape endemic.

Are invasive populations characterized by a broader diet than native populations?

“…The diet of X. laevis has been studied in its native range (Schoonbee, Prinsloo & Nxiweni, 1992; Vogt et al, 2017), and in different invasive populations (McCoid & Fritts, 1980; Measey, 1998a; Lobos & Measey, 2002; Faraone et al, 2008; Amaral & Rebelo, 2012; Courant et al, 2014). The first study carried out in the native range was performed in a fish farm (Schoonbee, Prinsloo & Nxiweni, 1992), which does not necessarily represent the typical diet of native populations.…”

An Evaluation of the Impacts of Alien Species on Biodiversity in South Africa Using Different Assessment Methods

“…Xenopus laevis (African Clawed Toad), native to South Africa but traded intensively globally, hybridises with the endemic X. gilli (Cape Platanna) (Picker 1985), but importantly there is no evidence of introgression (Furman et al 2017). Even though these two species might have likely overlapped for millennia (Schreiner et al 2013), densities of X. leavis have probably been artificially increased in the last 400 years (Measey et al 2017), leading to intense competition and predation (Vogt et al 2017;de Villiers et al 2016). Sclerophrys gutturalis (Guttural Toad), native to much of the country but introduced to a peri-urban area of Cape Town (Vimercati et al 2017), could potentially threaten the native endangered Sclerophrys pantherina (Western Leopard Toad), but no evidence of the extent of this threat has been reported to date (Measey et al 2017).…”

Experience and Lessons from Alien and Invasive Animal Control Projects in South Africa

“…However, the original range of X. laevis remains unclear (Measey et al 2017). Furthermore, research strongly suggests that the presence of X. laevis in the same water bodies reduces recruitment of X. gilli through competition and predation (De Villiers et al 2016;Vogt et al 2017;Thorp et al 2019). Early research suggested that introgression was a threat to X. gilli (Picker et al 1996), and this formed the basis of NEM:BA listing hybrids of X. gilli and X. laevis for removal.…”