ROBERT SIEGEL, Host:
On now to another long-running conflict: This one ecological.
On the savannahs of Africa, giant elephants are pitted against angry ant swarms that live in trees. And according to a new study, one of the worst things that could happen in this conflict is for the two sides to find peace.
NPR's John Nielsen has more.
JOHN NIELSEN: If trees could feel emotions, there is nothing that would scare them more than the sight of an approaching elephant, according Todd Palmer, an ecologist with the University of Florida at Gainesville.
TODD PALMER: Elephants eat trees. They don't eat parts of trees, they don't eat - they can eat a tree much like we would eat a cupcake.
NIELSEN: We reached Palmer on a cell phone at his research site in Kenya. That's where he goes to study a small African tree that has found a way to repel hungry elephants. Palmer says these trees ooze tasty sap that attracts nasty ants and then makes the ants even nastier. He says a single of these trees can hold 100,000 of the ants, which is very bad news for any elephant that decides to chow down on a branch.
PALMER: So imagine 100,000 ants streaming across the tree towards this point of disturbance. At some point, enough is enough and you're going to have a face covered in these biting, stinging ants.
NIELSEN: Palmer says he's watched these ants charge straight into an elephant's trunk, which is famously sensitive. Now, scientists call this kind of ant-tree alliance a mutualism, which has a kind of peaceful ring to it. But not in this case, according to Palmer.
PALMER: It's a co-evolutionary war. People think of mutualisms as are the friendly sort of situation where species are helping each other out but it - what really is a battlefield.
NIELSEN: And on this particular battlefield, a tiny insect trumps the biggest land animal on earth. But that got Palmer wondering. What would happen to the ant-tree alliance if the common enemy - elephants - was gone? To find out, he put great big fences up around some of his trees, which are known locally as whistling thorns. And then he watched them for 10 years.
Palmer expected these trees to flourish with no elephants around but no. Some of them grew half as fast as before and many died and all of them stopped producing that tasty sap. That drove off all the ants that had once guarded them from the elephants.
PALMER: These trees, in the absence of herbivores, decided, well, the herbivores are gone so it doesn't make a lot of sense to pay these ant- bodyguards, so let's reduce the salaries. In essence, they were paying these bodyguards.
NIELSEN: Palmer says the sap productions turned out to be a big mistake. That's because the guard ants were quickly replaced by other insects that attacked the trees, digging lots of ugly holes and tunnels.
PALMER: It's like the trees riddled with cancer or something, it's basically when you cut open a cross-section of a tree, it's all it is, is just this torn up inside with massive numbers of tunnels and dead branch systems everywhere.
NIELSEN: This is an experiment that shows just how powerful and complicated natural alliances can be, says Mark Bertness, a biologist with Brown University in Providence, Rhode Island. But more importantly, he says, it shows that you never know what you are going to get when you mess with Mother Nature.
MARK BERTNESS: This is a great example of how, without these mutualisms, the community collapses.
NIELSEN: Bertness says it's possible that similar collapses could take place in other parts of Africa, where elephant populations are now in trouble.
John Nielsen, NPR News, Washington.