Comparative Aspects of the Ecology of Four Syntopic Species of Angle- headed Lizards, Genus Gonocephalus (Reptilia: Agamidae: Draconinae).

Jye Wen, Wong and Indraneil, Das (2023) Comparative Aspects of the Ecology of Four Syntopic Species of Angle- headed Lizards, Genus Gonocephalus (Reptilia: Agamidae: Draconinae). Masters thesis, Universiti Malaysia Sarawak.

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Abstract

Investigations on coexistence and resource partitioning among sympatric species of reptilians have been widely conducted in other parts of the world but remain poorly studied in Borneo and other parts of south-east Asia. While some generalisations of ecological aspects may be applicable to local reptilian species, species interactions may differ, depending on geographical location and environment conditions. In the present study, four Gonocephalus species (G. bornensis, G. liogaster, G. doriae and G. grandis) were selected for a study of their comparative biology, the rationale being their perceived ecological similarity and syntopic occurrence, to develop a better insight of the ecological phenomena of resource partitioning. Studies on ecology, specifically on home range, habitat preference, diet and thermal biology, with additional records of parasite, colouration and predation of populations at Kubah National Park, Sarawak, East Malaysia (north-western Borneo) were carried out from June 2018 to December 2019. A total of 16 lizards, representing four species, were equipped with temperature sensitive radio-transmitters, permitting the collection of data on movement and body temperature. Species of Gonocephalus generally occupy similar microhabitats, favouring areas with gentle to moderate slope, high canopy cover, are plastic in their usage of trees in terms of sizes or height, moderate distance to waterbodies, on tree trunk, tree branch, moderate to high humidity, moderate to high ambient temperature, low to median light intensity and low to median perch surface temperatures. All had moderate home range sizes that were similar across species and sexes. Nonetheless, species of Gonocephalus diverge slightly along the spatial dimension of their ecological niches by exhibiting different levels of preference towards aspects of microhabitats utilised, while the lack of interspecific home range overlaps propose that these species are occupying different parts of the forest, although a more extensive sampling that include more individuals may be needed to confirm this. The four species were primarily shade-dwellers and have relatively low mean body temperatures. They exploit the thermal niche differently which are reflected from the spatial niche, and are likely influenced by the trophic niche. G. bornensis was overall a habitat generalist compared to its congeners, whereas G. doriae are relatively specialised. A total of 13 prey types were identified, consisting mainly of insects and other non-insect arthropod groups (earthworms and snails). However, there was insufficient evidence to conclude unequivocally that trophic resource partitioning contributed to coexistence among these species. Additionally, four nematode and three acarid species were successfully identified in these lizards. G. doriae serve as new host for Orneoascaris sp., and both G. bornensis and G. liogaster serve as new hosts for Strongyluris sp. Species of Gonocephalus displayed sexual dichromatism, where males are generally more colourful and vibrant compared to females. Individuals of the genus are able to quickly change skin colouration from dull to bright or vice versa for social interaction and thermoregulation. Furthermore, a G. liogaster was also found preyed upon by a Ptyas carinata, contributing to the list of predators of Gonocephalus. Overall, this study adds to the knowledge of these species and expands current understanding of resource partitioning and mechanisms of coexistence of lizard populations in Borneo's tropical rainforest, which may be beneficial for both conservation and management as well as future studies on other Bornean ectothermic species.

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