Browsing by Author "De Villiers, Francois Andre"

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    The dispersal ability, performance and population dynamics of Cape Xenopus frogs
    (Stellenbosch : Stellenbosch University, 2016-03) De Villiers, Francois Andre; Measey, John; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Dispersal is an important life history trait which is present in most organisms, and can affect the population structure, such as survival and age structure, of a species. An organism’s dispersal ability is related to the individual’s performance ability, which is ultimately determined by the individual’s morphology. Amphibians have been classically viewed as poor dispersers, but studies have shown that there are some exceptions. However, these studies represent terrestrial frog species and lack aquatic frog species. Frogs in the genus Xenopus are principally aquatic, and have been known to make use of water corridors for dispersal, however overland dispersal has been observed. There are two Xenopus present in the south Western Cape; X. gilli and X. laevis. In this study I compare and determine the dispersal ability, performance and morphology of X. gilli and X. laevis. I hypothesize that X. laevis will outperform X. gilli in both dispersal and relative performance. Two sites were used in this study; an area east of Kleinmond and the Cape of Good Hope section of TMNP (CoGH). In Kleinmond both X. laevis and X. gilli were marked with PIT tags, whereas only X. gilli was tagged in CoGH. Jumping and swimming performance was obtained by filming the frogs at 240fps, and wet and dry endurance was measured in a 4m track. Dispersal distances between two ponds were represented by Euclidean distances based on recapture of individually marked animals. The results show that X. laevis was the better jumper and swimmer of the two species. All performance trails that included jumping were found to be related to the leg morphology of the two Xenopus species. There was no difference in the dispersal distance of the two species, which was mirrored by the lack of difference in dry endurance; however Xenopus laevis had the highest proportion of individuals dispersing. Population structure is an important tool to determine the state of a given population. In a species that experiences high juvenile predation it is expected that the age structure would be skewed towards the older individuals and that the juveniles will have a low survival rate. Xenopus laevis poses a threat to X. gilli through predation, competition and hybridization. I compared the survival and age structure of X. laevis and the two X. gilli populations. I hypothesized that X. laevis will have a negative effect on the survival and age structure of X. gilli. Recaptures at Kleinmond and CoGH recurred between three to six weeks. The second phalange of the outer toe of 20 males and 20 females of X. laevis and X. gilli at both sites were sectioned. The number of lines of arrested growth (LAG) were recorded as a proxy for age. All frogs that were recaptured in 2015 were photographed again and growth was determined. The results indicate that Kleinmond X. gilli had the lowest survival (0.319), which was accredited to competition and predation by X. laevis, whereas CoGH X. gilli had the highest survival (0.562). Age structure was not determined possibly due to the presence of artificial water-bodies and consequently the lack of LAG production in some individuals.