The summit rat (''Rattus baluensis'') is a species of

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

in the family Muridae. It is found only on

Mount Kinabalu Mount Kinabalu ( ms, Gunung Kinabalu, Dusun: ''Gayo Ngaran or Nulu Nabalu'') is the highest mountain in Borneo and Malaysia. With an elevation of , it is third-highest peak of an island on Earth, and 20th most prominent mountain in the worl ...

and Mount Tambuyukon,

Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...

, 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 The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

. However, nowadays they are genetically isolated despite they are only 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". Diversity and Distributions, 24: 1252-1266. https://doi.org/10.1111/ddi.12761 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

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 Pitcher plants are several different carnivorous plants which have modified leaves known as pitfall traps—a prey-trapping mechanism featuring a deep cavity filled with digestive liquid. The traps of what are considered to be "true" pitcher p ...

, ''

Nepenthes rajah ''Nepenthes rajah'' is a carnivorous pitcher plant species of the family Nepenthaceae. It is endemic to Mount Kinabalu and neighbouring Mount Tambuyukon in Sabah, Malaysian Borneo.Clarke 1997, p. 123. ''Nepenthes rajah'' grows exclusively ...

''. 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.

References

* Rattus Endemic fauna of Malaysia Rodents of Malaysia Mammals described in 1894 Taxa named by Oldfield Thomas Mammals of Borneo Taxonomy articles created by Polbot {{Rattus-stub