For Seeds, Rodents Are Like Taxis

Jul 17, 2012
Originally published on July 17, 2012 12:17 pm



This next story takes on some new scientific research involving wily rodents, rodents that run around through the rainforest stealing mercilessly from one another. That doesn't sound very nice, but they're actually providing a service for the forest that may once have been provided by wooly mammoths.

NPR's Richard Harris could not resist telling a story with such an intriguing cast of characters.

RICHARD HARRIS, BYLINE: Before we get to the thieving rodents and the woolly mammoths, let me introduce another critical character. That would be a palm tree, trying to do what all trees do - reproduce.

BEN HIRSCH: If you're a tree, you want your seeds to go far away from you. Because seeds that fall directly underneath a parent tree tend not to do well.

HARRIS: Ben Hirsch, a postdoctoral researcher at Ohio State University, got interested in this tropical tree. Its seeds apparently evolved to appeal to wooly mammoths or similar large plant eaters. They are covered with sweet fruit. So the mammoth would presumably eat the fruit, and pass the seed somewhere down the trail.

HIRSCH: It's been assumed that these seeds were dispersed by these large, extinct mega fauna.

HARRIS: They went extinct 10,000 years ago, right? So explain the last 10,000 years.


HARRIS: That's exactly what Hirsch and his colleagues have done in a paper published in the Proceedings of the National Academy of Sciences. No other animal in the rainforest is big enough to swallow these seeds. Yet the tree persists. Turns out that six pound rodents, called agoutis, like to gather the seeds and stash them for eating later. The problem is agoutis tend to bury seeds near where they find them, so that doesn't explain how seeds get widely dispersed.

But Hirsch and his colleagues solved that mystery, by of all things, attaching radio transmitters to the seeds.

HIRSCH: We didn't find them eaten. We found them buried again. And then after that, then the seed was moved again and buried again. And moved and buried. And moved and buried.

HARRIS: Even though no single move was that far, these steps could add up. One seed ended up a quarter of a mile from where it started. So that could explain how these palm seeds get dispersed widely, even without wooly mammoths to help. But what's up with all this seed moving?

HIRSCH: We had one seed that was moved 36 different times. And this is one seed, so when we observed this we were stunned.

HARRIS: To figure out why this was happening, Hirsch and his colleagues tagged a bunch of agoutis and then set out cameras to watch over the seed hiding places. And they uncovered rampant thievery in the forest.

HIRSCH: So one agouti would take a seed and bury it. A different agouti would come and take that seed. And then a third agouti would then come and take that seed. Then sometimes, the original agouti would come back and get the seed back, and then it would get stolen again.

HARRIS: Ben Hirsch says he's not going to step into the academically treacherous debate over what these animals are up to; whether they are sharing a common food resource, or simply a bunch of thieves.

But Stephen Vander Wall, at the University of Nevada in Reno, says he thinks seed stashing is good all around; good for the tree and good for the rodent population as a whole. He's seen chipmunks steal pine seeds from one another in the Sierra, though not as impressively as the agouti.

STEPHEN VANDER WALL: It's probably a very common phenomenon for pilferage and recapturing to go on and move seeds around. And it's only starting to become appreciated.

HARRIS: And as more scientists use the high-tech tools, like radio transmitters on seeds and surveillance cameras in the woods, we're likely to learn of other intrigues in the forest.

Richard Harris, NPR News.

