Autecology of the Endangered Spiny Hill Turtle, Heosemys spinosa in Sarawak, Malaysia (Borneo)

Siti Nor Baizurah, Abd Malik (2021) Autecology of the Endangered Spiny Hill Turtle, Heosemys spinosa in Sarawak, Malaysia (Borneo). PhD thesis, Universiti Malaysia Sarawak.

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Abstract

In tropical forested regions, such as Borneo, knowledge on turtle biology remains inadequate, perhaps due to a combination of factors, including rarity, cryptic lifestyle, logistic issues, as well as the general lack of expertise, interest and opportunity available in the past for such research. Despite being on the IUCN Endangered species list, virtually nothing is known of the life history of Heosemys spinosa, the Spiny Hill Turtle. The main objective of this study is to provide detailed information on spatial, thermal and trophic biology of the target species, such knowledge valuable for understanding conservation requirements as well as enhancing knowledge of the life history of a rainforest obligate. Six individuals, consisting of two males and four females from Kubah National Park were fitted with radio-transmitters and tracked from Apr 2017 to Jan 2019, and a total of 251 locations were obtained. Home range estimates from Minimum Convex Polygon (MCP) were 1.68–60 ha and 0.43–3.45 ha using 95% KDE. These figures were not correlated to sex of individuals. Sexual and individual variation seen in cumulative distance displaced indicate males as the more explorative and active of the sexes, with mean monthly distances of 416.67 m; 148 m was noted for females. Body mass did not influence distances covered, although changes in temperatures (ambient and ground) were correlated with movement. The species showed a strong association with canopy density, as well as association with ground covers, such as logs, trees, water bodies, leaf litter, overground vegetation and boulders. A total of 11 individuals (with comprising individuals from other parts of Sarawak) was used to describe sexual dimorphism in the species, emphasizing variation in shell morphology and colouration. Growth trend showed an indeterminate pattern, with continuous growth post maturity and males of the species demonstrating a more rapid growth rate. The size of maturity of females in this population was inferred from the presence of areas of vdeossification interpreted as plastral hinges in a small individual (SCL 125 mm). Radiographs obtained from females demonstrate that a plastral hinge transverses the hyo�hypoplastral suture, and does not remain rigid throughout the year. Efficient resource utilization is governed by multilevel interactions between organisms and abiotic factors, which includes intraspecific and interspecific relationships, thus addressing the importance of sustainable ecosystems. The diet comprises of animal matter, with Coleoptera dominating; five viable indeterminate seeds, and two fungal species identified as belonging to the genera Boletus and Russula were recorded in the diet of the species. Plant matter was discovered to be the dominant dietary components (males: 60% and females: 79%). Trophic niche characteristics are not affected by seasonal changes and body size. Thermoregulation in ectotherms is linked to their physiological and behavioural changes. Multiple means employed to combat these changes, either through habitat selection, postural or peripheral vascular responses, typically involve careful considerations. Mean body temperature recorded was 21.14–33.63°C, and alteration in ambient temperature was not correlated to the core temperature, while, carapace temperature is affected by changes in ambient temperature. Additionally, carapace temperature was correlated to core body temperature, but tend to produce higher values than body temperatures, thus questioning the use of the former as a surrogate of body temperature in studies of thermoregulation in the species, and perhaps in all turtles. Habitat heterogeneity was found to be important, and specific refugium for behavioural thermoregulation and includes dense leaf litter, fallen logs and cavities. The study highlighted major aspects of the life histories of Heosemys spinosa that have relevance to understanding habitat requirements, hence of interest, among others, in the conservation and management of the species.

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