Endemism and diversity of small mammals along two neighboring Bornean mountains

Abstract

Mountains offer replicated units with large biotic and abiotic gradients in a reduced spatial scale. This transforms them into well-suited scenarios to evaluate biogeographic theories. Mountain biogeography is a hot topic of research and many theories have been proposed to describe the changes in biodiversity with elevation. Geometric constraints, which predict the highest diversity to occur in mid-elevations, have been a focal part of this discussion. Despite this, there is no general theory to explain these patterns, probably because of the interaction among different predictors with the local effects of historical factors. We characterize the diversity of small non-volant mammals across the elevational gradient on Mount (Mt.) Kinabalu (4,095 m) and Mt. Tambuyukon (2,579 m), two neighboring mountains in Borneo, Malaysia. We documented a decrease in species richness with elevation which deviates from expectations of the geometric constraints and suggests that spatial factors (e.g., larger diversity in larger areas) are important. The lowland small mammal community was replaced in higher elevations (from above ~1,900 m) with montane communities consisting mainly of high elevation Borneo endemics. The positive correlation we find between elevation and endemism is concordant with a hypothesis that predicts higher endemism with topographical isolation. This supports lineage history and geographic history could be important drivers of species diversity in this region.

Ancient Divergence Driven by Geographic Isolation and Ecological Adaptation in Forest Dependent Sundaland Tree Squirrels

“…Ecological field studies (Kemper and Bell, 1985;Sharma, 1992;Abdullah et al, 2001;Yasuda et al, 2003;Saiful and Nordin, 2004;Jayaraj et al, 2013) and diet data finding bark, fruit and insects (Harrison, 1962;Abdullah et al, 2001) are also consistent with an arboreal life style for S. robinsoni. On the other hand, S. lowii on Borneo seems to be much more terrestrial (Davis, 1962;Wells et al, 2004;Camacho-Sánchez et al, 2019) with a diet including small arthropods, fruits and fungus (Davis, 1962). The Fraternal squirrel seems to have intermediate habits, since it uses the ground extensively, but also climbs showing a preference for heights up to five meters, but avoids the upper canopy (Whitten, 1981).…”

“…Two of the treeshrews (Tupaia minor and Tupaia gracilis) and most of the squirrels are arboreal, and three of the latter are bark gouging specialists (Sundasciurus tenuis, Nannosciurus melanotis and Exilisciurus exilis) (Emmons, 2000;Zelditch et al, 2017). However, the only two terrestrial squirrels (Lariscus insignis or L. hosei and Rhinosciurus laticaudatus) are in very low densities or possibly absent where Low's squirrel is present (Wells et al, 2007;Yasuda and Tsuyuki, 2012;Fitzmaurice, 2014;Chapman et al, 2018;Camacho-Sánchez et al, 2019;authors unpublished data) and are specialized on fruits and insects. On Sumatra and the Malay peninsula S. robinsoni is co-distributed with diurnal arboreal and terrestrial treeshrews (Tupaia minor and T. glis/T.…”

“…Twelve samples were derived from tissue collected from historical specimens housed in three museums, 10 samples were modern tissue coming from museum loans and 14 sample sequences were downloaded from Genbank. Four samples were obtained from specimens collected during a previous expedition to Borneo (Camacho-Sánchez et al, 2019) and these were all taken according to the guidelines of the American Society of Mammalogists (Sikes, 2016) and as approved by Institutional Animal Care and Use Committees (Smithsonian Institution, National Museum of Natural History, proposal number 2012-04 and Estación Biológica de Doñana proposal number CGL2010-21424). Field research was approved by Sabah Parks [TS/PTD/5/4 Jld.…”

Little genetic structure in a Bornean endemic small mammal across a steep ecological gradient

“…Supporting this hypothesis, some studies of small mammals in Southeast Asia have found strong, cryptic genetic differentiation across elevations, such as in squirrels (den Hinckley et al, 2020;den Tex et al, 2010), shrews (Eldridge et al, 2018) and mice (Heaney et al, 2011;Justiniano et al, 2015). However, McCain (2009) suggest that these phenotypic changes, in combination with behaviours including diurnal activity patterns and nesting, may allow the species to persist across broad environmental conditions, which is rare among small mammals in this landscape (Camacho-Sanchez et al, 2019;Hinckley et al, in review;Nor, 2001). Further research is necessary to determine whether the phenotypic changes observed in mountain treeshrews in KNP are due to phenotypic plasticity, adaptive differentiation despite gene flow or a combination of these factors.…”

“…Our trapping methodology and permitting information is described in Camacho-Sanchez et al (2019). Briefly, we set traps from ~503 to 3,466 masl on MK and from ~331 to 2,509 masl on MT ( Figure 1a).…”