Veggie ants are a dangerous lot
an eerie feeling overwhelms you, the moment you step inside a rainforest. There are ants all over, hundreds of thousands of them crawling in the deep woods. The situation becomes creepier if you know they exist in abundance by defying the laws of nature.
Ants are supposed to be carnivores, so they should be near the top of the foodchain. By and large, each link in the web of life is a tenth the size of the one before it. This is because 90 per cent of the energy generated by the creatures in each link is used for metabolic processes, rather than being converted into flesh, blood, bones or exoskeletons. But a rainforest has more ants than arthropods (insects, spiders and other creepy-crawlies, that are devoured by the wingless creatures). Clearly, something strange is going on. Diane Davidson of the us-based University of Utah and her colleagues believe they know what it is: ants are not carnivores. Instead, they are crypto-vegetarians.
Davidson's theory is that most ants get their essential nitrogen from liquids exuded by sap-sucking insects, and not from gobbling other animals. "Ants can't get the liquids straight away from plants, as they have nasty chemicals to protect them from leaf-chewing herbivores. But the sapsuckers (treehoppers and scale insects) are unique because they bypass those defences. They have a tiny 'soda straw' in their mouth that they use to suck the sap. Therefore, the smart ants protect the sapsuckers from birds, wasps and flies, and in exchange eat their honeydew rich in sugar and amino acids," Davidson explains.
To test their idea, the researchers scrutinised isotopic composition of the ants, their animal prey and the plants from two tropical forests on opposite sides of the world -- one in Peru and the other in Borneo. In particular, they examined two isotopes of nitrogen: 14n and its heavier sibling 15n. These betray an animal's place in the foodchain because their ratio changes each time they are processed by an organism's metabolism, with 15n becoming more abundant. They found most ants have the same ratio of 15n as the leaf-chewing and sap-sucking insects.
Considering the number of ants around, the study has significant implications for rainforest ecology. It suggests that trees are under a lot more pressure from their fellow residents than people had realised. Since the ants protect the sapsuckers, they become more abundant. This is bad news, as it is these creatures who are among the most devastating herbivores of the rainforest. Food for our thought, and the ants.
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