Download A Unique Resource Mutualism between the Giant Bornean Pitcher Plant, Nepenthes rajah, and Members of a Small Mammal Community

Abstract

The carnivorous pitcher plant genus Nepenthes grows in nutrient-deficient substrates and produce jug-shaped leaf organs
(pitchers) that trap arthropods as a source of N and P. A number of Bornean Nepenthes demonstrate novel nutrient acquisition
strategies. Notably, three giant montane species are engaged in a mutualistic association with the mountain treeshrew, Tupaia
montana, in which the treeshrew defecates into the pitchers while visiting them to feed on nectar secretions on the pitchers'
lids. Although the basis of this resourcemutualism has been elucidated, many aspects are yet to be investigated.We sought to
provide insights into the value of the mutualism to each participant. During initial observations we discovered that the summit
rat, R. baluensis, also feeds on sugary exudates of N. rajah pitchers and defecates into them, and that this behavior appears to
be habitual. The scope of the study was therefore expanded to assess to what degree N. rajah interacts with the small mammal
community. We found that both T. montana and R. baluensis are engaged in a mutualistic interaction with N. rajah. T .montana
visit pitchers more frequently than R. baluensis, but daily scat deposition rates within pitchers do not differ, suggesting that the
mutualistic relationships are of a similar strength. This study is the first to demonstrate that a mutualism exists between a
carnivorous plant species and multiple members of a small mammal community. Further, the newly discovered mutualism
between R. baluensis and N. rajah represents only the second ever example of a multidirectional resource-based mutualism
between a mammal and a carnivorous plant.