Species diversity, distribution and morphological differences of monitor lizards (Family Varanidae) in southern Thailand

Abstract

The studies of species diversity, distribution and sexual dimorphism of monitor lizards were carried out from January 1998 to December 1999. Four species were found in southern Thailand, comprising Varanus salvator (Laurenti, 1768), V. rudicollis (Gray, 1845), V. bengalensis nebulosus (Gray, 1831) and V. dumerilii (Schlegel, 1839). V. flavescens (Hardwicke and Gray, 1827) and the Varanus salvator komaini Nutphand, 1987 were not found during the field survey. V. salvator and V. b. nebulosus distribute throughout southern Thailand in both forest and agricultural areas while V. rudicollis and V. dumerilii are usually found in undisturbed forests. The former three species distribute in three main mountain ranges (MR), i.e. Phuket MR, Nakhon Sri Thammarat MR and San Karakiri MR whereas the last is only found in Nakhon Sri Thammarat MR and San Karakiri MR. Morphological differences among monitor lizards in southern Thailand were studied using the analysis of variance (p<0.05). Some specific characters can be used to identify the species of monitors i.e. nuchal scale, snout-vent length, nostril length and nostril width. Sexual diference was studied in V. salvator, V. rudicollis and V.b. nebulosus using Mann Whitney U-test (p<0.05). All traits of male monitors were found to be longer and larger than that of the female monitors in all three species. Moreover, the Discriminant Function Analysis was applied to create equations for the prediction of the species and sexes of monitor lizards in southern Thailand as well. Morphological characters of V.s. komaini were compared to V. salvator. Both of them have similarity in most of their morphological characters. Considering the result from Canonical Discriminant Function, it could not be concluded that the V.s. komaini is a separate species or a subspecies of V. salvator. Some ecological and biological information of monitor lizards were studied. All species are being threatened by human disturbance. Based on the IUCN's criteria for the categories of threat, V. salvator and V. b. nebulosus are suggested to classified under in vulnerable category while V. rudicollis and V. dumerilii should be in endangered status. The V. s. Komaini is critically endangered and its natural habitat is still unknown.