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

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

in the family

Muridae The Muridae, or murids, are either the largest or second-largest family of rodents and of mammals, containing approximately 870 species, including many species of mice, rats, and gerbils found naturally throughout Eurasia, Africa, and Australia. ...

. It is found only on

Mount Kinabalu Mount Kinabalu ( Dusun: ''Gayo Ngaran'' or ''Nulu Nabalu'', ) is the highest mountain in Malaysia and Borneo. With a height of , it is the third-highest peak of an island on Earth, the 28th highest peak in Southeast Asia, and 20th most prom ...

and

Mount Tambuyukon Mount Tambuyukon or Tamboyukon (, Dusun: ''Nulu Tambuyukon'') is a mountain located at the West Coast and Kudat divisions of Sabah, Malaysia (located on the tripoints of three districts namely Ranau, Kota Belud as well as Kota Marudu). It ...

Malaysia Malaysia is a country in Southeast Asia. Featuring the Tanjung Piai, southernmost point of continental Eurasia, it is a federation, federal constitutional monarchy consisting of States and federal territories of Malaysia, 13 states and thre ...

, 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 geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

. 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". 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

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 carnivorous plants known as pitfall traps—a prey-trapping mechanism featuring a deep cavity filled with digestive liquid. The traps of pitcher plant are considered to be "true" pitcher plants and are formed by specialized ...

, '' 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.

References

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