Browsing by Author "Nieuwoudt, Cara Julia"

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    The effects of coastal lowland instability : melanism in Cordylus polyzonus and terrestriality in Cordylus macropholis
    (Stellenbosch : Stellenbosch University, 2001-12) Nieuwoudt, Cara Julia; Mouton, P. Le F. N.; Flemming, A. F.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: It has been suggested that rapid environmental change along the Western Cape coastal lowland has had a profound bearing on the evolution of cordylid populations in this region. To test a hypothesis on the evolution of melanism in the cordylid lizard, Cordylus polyzonus, the genetic relationship among melanistic, turquoise and brown morphotypes in this species was examined with allozyme electrophoresis. No polymorphic loci were found. No evidence was found that the melanistic population was genetically distinct from the other colour morphotypes. The results suggest that the studied melanistic population, is not a relict of a previously bigger melanistic population, but simply an ecotype within a larger gene pool. In the second section, some aspects of the ecology of the terrestrial lizard, Cordy Ius macropholis were investigated. Implications of a proposed hypothesis on habitat transition in this species, due to sea-level events, are discussed. Three complementary methods were used to investigate habitat selection in C. macropholis in a natural area of Strandveld Succulent Karoo vegetation. First, the sighting frequency of lizards in distinct plant categories was compared to the relative availability of the habitats. Except for one case, all .sightings of lizards were made in Euphorbia caput-medusae plants, the least available habitat category. Second, the habitat preference of C. macropholis in terms of shelter quality was examined. Given a choice of three shelter-types, both adult and juvenile lizards gave preference to E. caput-medusae, followed by rock crevices and plant debris. Prey availability in E. caput-medusae plants was also found to be consistent with prey items in the stomachs of C. macropholis at two independent sampling times. Results indicated that C. macropholis shows a distinct preference for the relatively scarce refuge, E. caput-medusae. Given the preference for such a scarce resource, one might expect C. macropholis to compete for potential mates that aggregate in these plants. To test this assumption, sex ratio, social structure, male spatial patterns and male social behaviour during the mating season were studied. Repetitive sampling of two populations revealed highly female-biased sex ratios. Sex ratio was found to relate positively to population density, as is the case in many polygynie lizard species. However, the composition of aggregations pointed to a monogamous mating structure for this species. In individual plants, segregation among adult males, and between adult males and juvenile males was significantly higher within the reproductive season than outside. Adult males also maintained a uniform spatial distribution within the reproductive season. Moreover, staged encounters indicated that adult males behaved aggressively among themselves and toward juvenile males, during the mating season. The data suggest that adult C. macropholis males are territorial and that less dominant males may be excluded from E. caput-medusae plants to habitats where their chances of survival may be lower. By implication, one might predict that grouping behaviour in C. macropholis is not well manifested and that movement of individuals among plants is high. This assumption was validated by analyzing the size and stability of groups, as well as movement patterns among plants. The size of aggregations within E. caput-medusae plants ranged from one to 14 individuals. Grouping was a year-round phenomenon, but aggregations exhibited a low degree of long-term social structure. Site fidelity was low, with females showing significantly higher site fidelity than males. Movement of individuals in and out of a marked population was high. Results suggested no differential movement patterns between the sexes. The data confirmed that aggregation behaviour and high degree of movement in C. macropholis are the result of mutual competition for a limited plant resource.