Effective conservation of melanistic lizard species in the Greater Cederberg Biodiversity Corridor

[摘要] ENGLISH ABSTRACT: The Cape Floristic Region (CFR) is a biodiversity hotspot in South Africa, threatened by climate change and various other processes. The Greater Cederberg Biodiversity Corridor (GCBC) is a conservation area incorporating both public and private land, providing a practical and effective solution to conserve biodiversity in the CFR. This area is also home to two of the eight melanistic cordylid lizard species found in south-western South Africa. One of the herpetological conservation targets identified for the GCBC was an understanding of the ecology of melanistic cordylid populations with particular reference to global environmental change.Most melanistic cordylids occur in cool coastal and montane localities, and it was suggested that melanism has a thermoregulatory function in these species. The first aim of this study was to determine the climatic conditions with which melanistic cordylids are currently associated. Several melanistic cordylid populations showed a distinct association with a high incidence of fog and cloud cover, underscoring the thermal melanism hypothesis, which predicts that melanistic lizards should occur in cool environments. Several other populations, however, did not show such an association.The next aim was thus to compare habitat use and morphology among 10 melanistic cordylid populations. Individuals of the northern population of Pseudocordylus capensis and the Cordylus peersi population occurred in the warmest environments, used significantly higher rock formations, and had relatively longer limbs than those of other melanistic populations. Having a morphology that allows for flexibility in habitat use, may enable species such as P. capensis to overcome the constraints of melanism in warm environments.Being melanistic may result in decreased activity times in warm environments. The variation in habitat thermal quality and daily activity patterns of two melanistic cordylid species with different morphologies and habitat preferences, occurring sympatrically, was investigated. During summer, high rocks provided a better thermal quality habitat to P. capensis than small rocks, and P. capensis had a longer activity period than C. oelofseni. This suggests that the thermal opportunities provided by high rock enables P. capensis to increase its activity time.The impact of terrestrial and aerial predators can help shape body armour in lizards, with those species more exposed to aerial predators being faster and less armoured, and those more exposed to terrestrial predators being more heavily armoured. The degree of body armour in melanistic cordylids and their non-melanistic relatives was investigated. Melanistic members of the cordylus-niger-oelofseni and C. polyzonus clades had less armour than their non-melanistic relatives, supporting the prediction that melanistic cordylids basked more and were more exposed to aerial predators than non-melanistic lizards. An increase in body armour in C. peersi indicated exposure to terrestrial predators, whereas P. capensis had a reduction in body armour, indicating exposure to aerial predators. Little body armour, together with a slender morphology and long limbs, may thus enable this species to move with ease on large boulders and scale vertical surfaces to successfully avoid predators.Pseudocordylus capensis displayed much greater movement rates during activity than other cordylids. A less sedentary foraging strategy may be a prerequisite for life on large, barren rock surfaces where food availability may be low or not uniformly distributed. Both males and females of this species also had large home ranges, a unique phenomenon for cordylids. Space use of males only overlapped marginally, but extensive overlap among males and females and among females, respectively, was observed.Due to the constraining effect of climate on the distribution of most melanistic populations, melanistic cordylids should be considered as priority species for conservation.While P. capensis is pre-adapted for survival in warm climates, it is dependent on the availability of suitable habitats. The GCBC would thus play an important role in the conservation of this species' habitat.

[发布机构] Stellenbosch University