Thousands of years ago, massive elephantlike creatures wandered the landscape, where they gobbled up, and then defecated, fruit. In the process, they may have planted the seeds for early forests. Yet with these creatures long extinct, ecologists have been left with a puzzle: If the same trees are still with us, what—if anything—disperses their seeds to create today's woodlands?
The answer—at least for one type of tree—may lie in the criminal antics of a cunning rodent. A group of scientists working with the Smithsonian Tropical Research Institute in Panama and Wageningen University in the Netherlands, along with other institutions, reports that by repeatedly raiding each other's stashes, these creatures spread seeds over a much wider territory than scientists had previously recognized. Dispersal is a key factor in ensuring the survival of a species because spreading individuals over a broader range can mitigate the effects of pests, move organisms into new climatic ranges and increase the flow of genes between populations.
The rodent in question is the agouti—a house cat–size critter that resembles a tail-less squirrel. The researchers studied agoutis caching black palm tree seeds on Barro Colorado Island in the Panama Canal over one year. They set up video cameras at cache sites, attached a long thread with a transmitter unit to each of 589 seeds and radio-tracked them. More than half of the seeds cached were stolen by other agoutis and recached elsewhere, traveling as far as 280 meters from their original locations. Ultimately agoutis or other small mammals ate most of the seeds, but around 14 percent most likely grew into seedlings. The findings were published in the July 31 Proceedings of the National Academy of Sciences USA.
The work casts doubt on the hypothesis that megafauna were crucially responsible for seed dispersal thousands of years ago because rodents may have played a role even then. Co-author Ben Hirsch of Ohio State University and his colleagues also believe their findings offer some hope for trees in the face of modern mammalian extinctions. That a humble rodent can step into the role left by long-lost megafauna is a testament to nature's resilience.
COMMENT AT ScientificAmerican.com/oct2012