Summit rat

 ( Rattus ) 

The summit rat ( Rattus baluensis) is a species of rodent in the family Muridae. It is found only on Mount Kinabalu and /ref> Malaysia, and has been recorded at altitudes of 2,040 to 2,477 m on Mt. Tambuyukon and 2,670 to 3,426 m on Mt. Kinabalu. They are most abundant in higher altitude dwarf forest and montane scrubland. The rat populations from these two peaks were connected in the Holocene. However, nowadays they are genetically isolated despite being 18 km apart.Miguel Camacho-Sanchez, Irene Quintanilla, Melissa T. R. Hawkins, Fred Y. Y. Tuh, Konstans Wells, Jesus E. Maldonado and Jennifer A. Leonard. 2018. "Interglacial refugia on tropical mountains: novel insights from the summit rat (Rattus baluensis), a Borneo mountain endemic" /ref> With current predictions of Global warming, the suitable habitat for Rattus baluensis is expected to shift around 500 m upwards. This will put the population in Mount Tambuyukon at risk. However, the population in Mount Kinabalu will likely survive in its upper slopes. Genetic analysis situate its origin in a local population of Rattus tiomanicus from northern Borneo at around 300-400 thousand years ago.

The summit rat has a mutualistic relationship with a species of giant pitcher plant, Nepenthes rajah. Like the treeshrew Tupaia montana, it defecates into the plant's traps while visiting them to feed on sweet, fruity secretions from glands on the pitcher lids.Greenwood, M., C. Clarke, C.C. Lee, A. Gunsalam & R.H. Clarke 2011. A unique resource mutualism between the giant Bornean pitcher plant, Nepenthes rajah, and members of a small mammal community. PLoS ONE 6(6): e21114. Wells, K., M.B. Lakim, S. Schulz & M. Ayasse 2011. Pitchers of Nepenthes rajah collect faecal droppings from both diurnal and nocturnal small mammals and emit fruity odour. Journal of Tropical Ecology 27(4): 347–353.