Bat faeces on the menu for southeast asian pitcher plant
Carnivorous pitcher plants in Brunei are feasting on bat faeces in an unusual mutualistic relationship. To survive in nitrogen deprived soil most pitcher plants lure in and digest passing insects, but the species, Nepenthes rafflesiana elongata, has adopted a novel strategy.
Often bats roost in groups in caves or trees but this is not the case for Hardwicke woolly bat, Kerivoula hardwickii, which has chosen to take up residence exclusively inside the pitcher of N.r.elongata. The aerial pitcher of the elongata plant is four times longer than other related pitcher plants. This extra room has allowed the plant to become the perfect roosting spot for a solitary wooly bat to shelter in during the day.
Studies have shown that N.r.elongata has a low insect capture rate compared to other pitcher plants suggesting reduced insect feeding. To make up for this nearly 34% of the plants nitrogen comes from bat faeces. In return for the much needed nutrients the plant provides shelter and protection to the bats from predators, solar radiation and rain.
The fluid level of the digestive acids used to dissolve insects is reduced in the elongata pitcher.This along with the elongation of the pitcher allows plenty of space for mothers and juveniles to stay together for several weeks to months roosting in a single plant. The plant has even developed a ‘girdle’ to prevent the bats from sliding into the pool of deadly liquid.
This type of vertebrate – plant mutualistic relationship is rare and there is only one other known example of this occurring between a carnivorous plant and a mammal. Another species of Nepenthes pitcher plant, also found in Borneo, is utilising faeces-trapping to gain vital nutrients although this time from a tree shrew. Rather than using the plant for shelter the trees shrew benefits from feeding on the plants nectar, the shrew will then defecate into the pitcher to mark its territory.
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