The Borneo Hills diet: Pitcher plants strange prey ift.tt/1fG8l3w Continue reading page |1|2 |3 Video: Tree shrew dines and defecates in toilet plant Instead of catching insects, some carnivorous pitcher plants target much bigger animals – but not to eat them. Watch out for a surprise on the menu HIGH in the misty mountains of Borneo, death awaits the unsuspecting wanderer. This is the lair of the most awesome of the pitcher plants, with fearsome traps and a reputation to match. The pitcher plants of south-east Asia are famed for their carnivorous habits. These merciless killers lure insects to the top of their traps with sweet nectar, where many lose their grip on the ultra-slippery rim and fall into the fluid-filled trap. As the victims desperately try to climb out, they discover too late that this is no ordinary fluid – it is filled with invisible stretchy fibres, and the more an insect struggles, the more entangled it becomes. Sooner or later the trapped animals drown, and digestive enzymes in the fluid accelerate the breakdown of their rotting corpses. Only then does the plant gets its reward: nitrogen, a key nutrient that is in short supply in the places where these killers lurk. Small insects, particularly ants, are the usual prey of the 120 or so species of Nepenthes plants. But the island of Borneo is home to several spectacular species with unusually shaped giant pitchers. The largest, Nepenthes rajah, has jug-like pitchers so big they can hold several litres of fluid, and its appetite is legendary. In the century-and-a-half since its discovery, there have been sporadic reports of it catching rats. So has the king of carnivorous plants really evolved to catch small mammals? After staking out the giant pitchers and mounting 24-hour surveillance, ecologists have discovered that the truth is even stranger than this. It turns out that N. rajah and at least three other pitcher plants in Borneo have indeed evolved to lure small mammals into their traps – but not to kill them... Yes, the tree shrew is doing what you think its doing on the pitcher plant (Image: Chien Lee/Minden Pictures) One of the first to suspect that some pitcher plants do things differently was Charles Clarke of Monash University Malaysia. During an expedition to Mount Pagon in north-west Borneo in the 1990s, he took a close look at one of the weird giant pitcher plants, called N. lowii (see picture). He noticed that its pitchers lack the slippery rim and smooth inner walls that help trap insects. N. lowii is odd in other ways too: the rim is unusually narrow and the mouth unusually broad, while the leafy lid that normally keeps out rain is angled up and away from the opening. And while other pitchers secrete nectar from glands around the rim, this plant oozed much larger quantities of thicker, buttery nectar from the underside of its lid. Finally, the whole structure – both the pitcher and the tendril it dangles from – is reinforced with woody lignin. All this suggests that this plant has evolved to attract something larger and heavier than insects to its pitchers. Growing pitchers is costly for a plant, so if the pitcher is much bigger than required you have to ask why, says Jonathan Moran of Royal Roads University in Canada. Could its prey be a nectar-sipping bird? Or a sweet-toothed mammal? In 2008, Clarke, Moran and colleagues found the answer in the cloud forest of Gunung Mulu in another part of Borneo. Keeping watch on N. lowii pitchers they found only one vertebrate visited them: the mountain tree shrew, Tupaia montana. Intrigued, Ulrike Bauer, a member of the team from the University of Cambridge, set up cameras. Her footage revealed how tree shrews leap onto the pitchers narrow rim and grip it with their hind feet before stretching up, across the yawning chasm to reach the nectar oozing from the lid. With a few wipes of a muscular tongue, the lids are clean and the tree shrews scamper off unharmed. It is all over in seconds. So N. lowii does not prey on shrews. But it does not go unrewarded: the footage revealed that the tree shrews sometimes pooped in the pitcher. Clarke had noted on his earlier expedition that the pitchers contained few insects but a lot of droppings. The video evidence suggested that this is no accident: N. lowii not only looks like a toilet – it is a toilet for tree shrews. An unusual relationship The orientation of the lid forces the tree shrew to position its rear end over the pitchers mouth while feeding, says Moran. That increases the chances of faeces being captured if the animal defecates while its on the pitcher. It also means that any droppings left sticking to the walls of the pitcher are flushed to the bottom when it rains. With tree shrews weighing around 150 grams, this also explains why the pitchers are more robust than those of insect catchers. If they werent reinforced theyd probably snap off, says Moran. Continue reading page |1|2 |3 Subscribe to New Scientist and youll get: New Scientist magazine delivered every week Unlimited access to all New Scientist online content - a benefit only available to subscribers Great savings from the normal price Subscribe now! If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.
Posted on: Mon, 03 Feb 2014 16:34:27 +0000
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