Biology subjects

Tangah, J.

Publications and source records attributed to Tangah, J..

5 recordsLinked to original sources

bioRxiv2026

Long-term Population Dynamics and Conservation of Proboscis Monkeys (Nasalis larvatus) in the Lower Kinabatangan, Sabah, Malaysia

Long-term ecological monitoring is essential for evaluating the effectiveness of conservation actions for long-lived tropical primates, yet few studies have integrated repeated population censuses with habitat-change analyses. We evaluated long-term population and habitat dynamics of the endangered proboscis monkey (Nasalis larvatus) in the Lower Kinabatangan, Sabah, Malaysian Borneo, by integrating a landscape-wide population survey conducted in 2025 with previous surveys from 2005 and 2014, long-term monitoring at three representative sites, and spatial analyses of land-use and land-cover change. Standardized late-afternoon boat-based surveys covering approximately 223 km of the Kinabatangan River and its tributaries recorded an estimated 2,420 individuals in 174 social groups, representing an increase of approximately 66% and 72% respectively compared with the 2005 survey. Group sizes (number of individuals per social group) remained largely unchanged despite the overall increase in population size. Long-term monitoring at three representative sites indicated stable population trajectories throughout the study period. Habitat analyses further revealed an increase in natural vegetation and limited conversion of forest to oil palm within protected areas between 2005 and 2025. Together, these independent lines of evidence indicate that the Lower Kinabatangan proboscis monkey population has recovered while maintaining overall demographic stability under long-term habitat protection. Nevertheless, substantial areas of suitable habitat remain outside the protected-area network, highlighting opportunities for additional habitat restoration and improved landscape connectivity. Our findings demonstrate the value of integrating long-term ecological monitoring with landscape-scale habitat assessment to inform adaptive conservation management in fragmented tropical landscapes.

ecology↗

bioRxiv2026

Spatial patterns of mosquito communities and monkey malaria vectors in a tropical riverine forest in Sabah, Malaysian Borneo

Understanding how vector ecology intersects with host behaviour is essential for predicting zoonotic disease risk in tropical ecosystems. We conducted a two-year field study (November 2016-October 2018) in a riverine forest in Sabah, Malaysian Borneo, to characterize mosquito communities and the spatial distribution of potential simian-malaria vectors. Mosquitoes were sampled on 44 nights using CO{square}-baited light traps repeatedly deployed along a 500 m transect at three distances from the river (0, 250, 500 m) and two vertical strata (ground and canopy), yielding 244 trap collections across repeated sampling nights. In total, 9,928 mosquitoes were collected, dominated by Culex spp. (9,079; 91.4%), whereas Anopheles spp. were rare (153; 1.5%); most remaining specimens were unidentified to genus, and species-level identification was limited primarily to Anopheles. Nevertheless, female Anopheles (n=57) were more frequently detected near the river and less commonly at intermediate distance, and tended to be captured more often in ground traps. Zero-inflated negative binomial GLMMs based on the full mosquito dataset indicated significant effects of river distance and height on mosquito abundance, while night-time temperature and humidity showed no detectable effects. The zero-inflated structure of the data further suggested that many zero captures reflected true absence rather than sampling variability. The Anopheles assemblage was dominated by An. balabacensis, and molecular screening of 57 females detected simian Plasmodium DNA in two individuals. Overall, these findings suggest that river-edge habitats may represent localized areas where vectors persist and where primates and human activities overlap, creating repeated opportunities for host-vector contact even when vector densities are low.

ecology↗

bioRxiv2025

Impact of Group Size and Habitat Disturbance on Parasitic Infection in Free-ranging Proboscis Monkeys

Group-living primates experience the benefits and costs associated with sociality, including an elevated risk of parasite transmission. However, the relative influence of group type (i.e., social structure), group size, and habitat disturbance on parasitic infection remains unclear, particularly in Southeast Asian primates. In this study, the abundance of intestinal parasites in proboscis monkeys (Nasalis larvatus) inhabiting a riverine forest along the Menanggul River, Sabah, Malaysian Borneo, was investigated. Fecal samples (n = 160) were collected from one-male-multifemale and all-male groups in areas with varying levels of anthropogenic disturbance, with efforts made to ensure that each sample originated from a different individual. In addition, the effects of group type, group size, and sampling location on parasite abundance were evaluated using fecal egg counts and Bayesian models. Three dominant parasite species groups (Trichuris sp., Strongyloides fuelleborni, and Oesophagostomum aculeatum) with an overall infection prevalence of 81.25% were identified. Results showed that group type did not significantly affect parasite abundance. However, group size showed a positive correlation with the abundance of Trichuris sp. and a negative correlation with S. fuelleborni and O. aculeatum. In addition, our models revealed that the infection load of Trichuris sp. decreased with increasing distance from the river mouth, which was used as a proxy for a disturbance gradient, whereas O. aculeatum exhibited higher infection load at greater distances, indicating lower prevalence in more disturbed downstream areas. Thus, parasite abundance in proboscis monkeys may be shaped by social and environmental factors, with taxa-specific responses likely reflecting differences in environmental persistence and transmission ecology.

ecology↗

bioRxiv2023

Gut microbial community in proboscis monkeys: implications for effects of geographical and social factors

Recent technological advances have enabled comprehensive analyses of the previously uncharacterized microbial community in the gastrointestinal tracts of numerous animal species; however, the gut microbiota of several species, such as the endangered proboscis monkey (Nasalis larvatus) examined in this study, remains poorly understood. Our study sought to establish the first comprehensive data on the gut microbiota of free-ranging foregut-fermenting proboscis monkeys and to determine how their microbiota are affected locally by environmental factor, i.e. geographical distance, and social factor, i.e. number of adult females within harem groups and number of adults and subadults within non-harem groups, in a riparian forest in Sabah, Malaysian Borneo. Using 16S rRNA gene sequencing of 264 faecal samples collected from free-ranging proboscis monkeys, we demonstrated the trend that their microbial community composition is not particularly distinctive compared to other foregut and hindgut fermenting primates. The microbial alpha diversity was higher in larger groups and individuals inhabiting diverse vegetation (i.e. presumed to have a diverse diet). For microbial beta diversity, some measures were significant, showing higher values with larger geographical distances between samples. These results suggest that social factors such as increased interindividual interactions, which can occur with larger groups, as well as physical distances between individuals or differences in dietary patterns, may affect the gut microbial communities.

microbiology↗

bioRxiv2020

Factors influencing riverine utilization patterns in two sympatric macaques

Many species of terrestrial animals, including primates, live in varied association with the aquatic (e.g., riverine or coastal) environment. However, the benefits that each species receive from the aquatic environment are thought to vary depending on their social and ecological characteristics, and thus, elucidating those benefits to each species is important for understanding the principles of wild animal behaviour. In the present study, to gain a more complete picture of aquatic environment use, including social and ecological factors in primates, factors affecting riverine habitat utilization of two macaque species (Macaca nemestrina and M. fascicularis) were identified and qualitative comparisons were made with sympatric proboscis monkeys (Nasalis larvatus), which have different social and ecological characteristics. Temporal variation in sighting frequency of macaques at the riverbanks was positively related to the fruit availability of a dominant riparian plant species and negatively related to the river water level which affects the extent of predation pressure. Riverine utilization of macaques was greatly influenced by distribution and abundance of food (especially fruit) resources, possibly in association with predation pressure. Additionally, qualitative ecological comparisons with sympatric proboscis monkeys suggest that the drivers of riverine utilization depend on the feeding niches of the species, and different anti-predator strategies resulting from their differing social structures.

ecology↗