Results - A geographical analysis of melanistic cordylid lizard

By Julie Foster,2014-10-25 18:29
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Results - A geographical analysis of melanistic cordylid lizard

Results for some of the student projects

    Project: Morphological and behavioral correlates of melanism (Dahné du Toit, Ph.D. student)

    As part of her Ph.D. study on melanistic cordylids, Dahné investigated the climatic conditions associated with the distribution of these species. A summary of the results is presented here.

    Most melanistic (black) cordylid lizard species occur in small populations along the west coast of South Africa and in the western parts of the Cape Fold Mountains. However, there are two exceptions. In contrast to the coastal or montane distribution of most of these species, Peers’Girdled Lizard (Cordylus peersi) is found in Namaqualand, and in contrast to the limited

    distribution ranges of most species, the Graceful Crag Lizard (Pseudocordylus capensis) has a

    relatively wide distribution. A detailed analysis of the geographical distribution of melanistic cordylid species, and a search for climatic correlates to explain the observed patterns of distribution,

    were conducted. A geographic

    information system (GIS) was used

    to determine altitude, minimum

    temperature, maximum temperature,

    potential evaporation, precipitation,

    solar radiation, fog, and cloud cover

    for each locality. Data were

    analyzed by means of a Principal

    Component Analysis (PCA).

    Melanistic species with restricted

    distribution ranges were

    characterized by a specific set of

    climatic variables, while the more

    widespread species spanned a wide

    range of climatic conditions. In

    general, there was a good correlation between the distribution of coastal and montane populations and cool climatic conditions. Coastal species were mainly associated with a high incidence of fog and minimum temperatures, while montane species were associated with cloud cover and rainfall. A dark body would absorb radiant energy more efficiently than a light body, and melanism is thus often considered an advantage in a cool environment. However, this correlation does not hold true for all melanistic species, as Pseudocordylus capensis and Cordylus peersi were associated with

    warmer climatic conditions. This suggests that these two species have a broader tolerance range for warm climatic conditions than other melanistic cordylids, or that these species occupy very specific habitats within their distribution range. A regional scale analysis of climatic variables will not reveal the climatic conditions associated with specific microhabitats. A fine-scale investigation of the microhabitats- and climates associated with these species was conducted in order to better understand the ecology of melanistic cordylids in warm climates. Results will be available soon.

    Project: Armadillo lizards and termites (Cindy Shuttleworth, M.Sc. student)

    Cindy recently completed her M.Sc. thesis and received her degree in December 2006. Several articles are being prepared for publication and will be posted as they become available. A summary of her work is presented here.

The role of the southern harvester termite, Microhodotermes viator, and several climatic

    parameters in the distribution of the group-living lizard, Cordylus cataphractus, was investigated.

    Microhodotermes viator is considered the most important prey item of C. cataphractus and

    termitophagy as the causative agent in the evolution of group-living in this species. One would therefore expect a high degree of correspondence in the ranges of C. cataphractus and M. viator.

    As climate will also play a role in the distribution of any

    species, various climatic variables were investigated to

    determine their influence on the distribution of C.

    cataphractus. Species distributions were visualized

    using the minimum polygon technique and the degree

    of overlap was determined using standard geographic

    information systems (GIS) techniques. A total of 52 C.

    cataphractus localities were investigated for the

    presence of termites. The climatic limits of the

    geographical distribution of C. cataphractus were