Ecological relationships

Ecological relationships

A drowned lizard found in a freshly opened pitcher of N. rajah

The most obvious interaction between Nepenthes species and its environment, including other organisms, is that of predator and prey.Nepenthes species certainly attract and kill their prey, albeit passively, through active production of attractive colours, sugary nectar, and even sweet scents. From this relationship, the plants primarily gain nitrogen and phosphorus to supplement their nutrient requirements for growth, given that soil nutrients are typically lacking. The most frequent prey is an abundant and diverse group of arthropods, with ants and otherinsects topping the menu. Other arthropods that are found frequently include spiders, scorpions, and centipedes, while snails and frogs are more unusual but not unheard of. The most uncommon prey for Nepenthes species includes rats found in N. rajah. The composition of prey captured depends on many factors, including location, but can incorporate hundreds of individual insects and many different species.^[2] While many Nepenthes are generalists in what they capture, at least one, N. albomarginata, has specialised and almost exclusively traps termitesand produces nearly no nectar. Nepenthes albomarginata gains its name from the ring of white trichomes that are directly beneath the peristome. These trichomes—or "hairs"—are palatable to termites and will attract them to the pitcher. In the course of collecting the edible trichomes, hundreds or thousands of termites will fall into the pitcher.^[12][13]

A lower pitcher of N. attenboroughiisupporting a large population of mosquito larvae. The upright lid of this species exposes its pitchers to the elements such that they are often completely filled with fluid.^[14]

[edit]Symbioses

Nepenthes bicalcarata provides space in the hollow tendrils of its upper pitchers for the carpenter ant Camponotus schmitzi to build nests. The ants take larger prey from the pitchers, which may benefit N. bicalcarata by reducing the amount of putrefaction of collected organic matter that could harm the natural community of infaunal species that aid the plant's digestion.^[15]

Nepenthes lowii has also formed a dependent relationship, but this time it is with vertebrates instead of insects. The pitchers of N. lowii provide a sugary exudate reward on the reflexed pitcher lid (operculum) and a perch for tree shrew species, which have been found eating the exudate and defecating into the pitcher. A 2009 study, which coined the term "tree shrew lavatories", determined that anywhere between 57 and 100% of the plant's foliar nitrogen uptake comes from the faeces of tree shrews.^[16] Another study published the following year showed that the shape and size of the pitcher orifice of N. lowii exactly match the dimensions of a typical tree shrew (Tupaia montana).^[17][18] A similar adaptation was found in N. macrophylla and N. rajah, and is also likely to be present in N. ephippiata.^[18]

[edit]Infauna

Main article: Nepenthes infauna

Organisms that spend at least part of their lives within the pitchers of Nepenthes species are often called Nepenthes infauna. The most common infaunal species, often representing the top trophic level of the infaunal ecosystem, are many species of mosquito larvae. Other infaunal species include fly and midge larvae, spiders, mites, ants, and even a species of crab (Geosesarma malayanum). Many of these species specialise to one pitcher plant species and are found nowhere else. These specialists are called nepenthebionts. Others that are often associated but are not dependent on Nepenthes species are called nepenthophiles. Nepenthexenes, on the other hand, are rarely found in the pitchers, but will often appear when putrefaction approaches a certain threshold, attracting fly larvae that would normally not be found in the pitcher infaunal community. The complex ecological relationship between pitcher plant and infauna is not yet fully understood, but it has been suggested that the relationship is mutualistic: the infauna is given shelter, food, or protection and the plant that harbours the infauna receives expedited breakdown of captured prey, increasing the rate of digestion and keeping harmful bacterial populations repressed.^[15][19][20]