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 resource mutualism 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.

Phylogenetic analysis of niche divergence reveals distinct evolutionary histories and climate change implications for tropical carnivorous pitcher plants

“…Our results show that the higher altitude species will lose a greater amount of potentially suitable habitat by 2070 compared to the lower species (Table 2). Habitat shifts would need to account for interactions concerned with diet (Moran, 2001;Merbach et al, 2002;Clarke et al, 2009;Greenwood et al, 2011), symbiotic specializations (Bonhomme et al, 2011;Rembold et al, 2012) and pollinators. It is estimated that some habitats may disappear completely as a result of the current and predicted climate change (Williams et al, 2007).…”

Tuning of color contrast signals to visual sensitivity maxima of tree shrews by three Bornean highland Nepenthes species

“…11,18 Further, it has been demonstrated that N. rajah pitchers produce volatiles that attract small mammals. 11 The possible role of volatiles in attraction of tree shrews to N. lowii and N. macrophylla pitchers awaits further investigation.…”

CarnivorousNepenthespitcher plants are a rich food source for a diverse vertebrate community

“…Birds such as Mountain Blackeyes (Chlorocharis emiliae) have also occasionally been observed feeding on the N. lowii lid secretion (Phillipps et al 2008). Nepenthes rajah, another species from the high mountains of Sabah that reportedly attracts tree shrews (T. montana) and summit rats (Rattus baluensis) and captures their faeces (Greenwood et al 2011;Wells et al 2011), shows similar adaptations of its pitcher morphology (Figure 1d). The size and shape of the pitcher opening has been shown to be strongly correlated with the body size of the tree shrews (Chin et al 2010).…”

“…While most Nepenthes trap insects, some species have recently been shown to engage in mutualistic relationships with vertebrates (Clarke et al 2009;Grafe et al 2011;Greenwood et al 2011). In these exceptional cases, the plant has evolved specific adaptations to attract small mammals.…”