Rodents’ takeover from elephants in Panamanian rainforests

This video is called Movement paths of 224 radio-tagged palm seeds by rodents on Barro Colorado Island, Panama.

It says about itself:

Relative movement paths of 224 radio-tagged palm seeds handled by rodents on Barro Colorado Island, Panama. Colored dots mark locations of 129 seeds that were found eaten (orange), 86 seeds last seen before they lost their tags (gray), and 9 seeds that were still alive, cached, and being monitored after a year (pink).

Smithsonian Tropical Research Institute, Panama. By attaching tiny radio transmitters to more than 400 seeds, Patrick Jansen, scientist at the Smithsonian Tropical Research Institute and Wageningen University, and his colleagues found that 85 percent of the seeds were buried in caches by agoutis, common, house cat-sized rodents in tropical lowlands. Agoutis carry seeds around in their mouths and bury them for times when food is scarce.

By Ajai Raj:

Thieving rodents saved tropical palm

Monday, 16 July 2012

SYDNEY: An innovative seed-tracking study in the Panamanian rainforest has solved the mystery of how the black palm tree spreads its seeds.

Until now, how the black palm (Astrocaryum standleyanum), a spiny palm trees native to Central and South America, dispersed its seeds has been a mystery. Its seeds, big and heavy compared to other seeds, were likely once eaten by enormous megafauna, which later pooed out the seeds further afield. However, the last of these went extinct at the end of the Pleistocene epoch, over 10,000 years ago – so how is the tree still here?

To figure it out, researchers used an innovative seed-tracking study, radio-tagging about 600 black palm tree seeds and placing them at stations across Barro Colorado Island, which were monitored with motion-sensitive cameras.

Seed stolen and moved 36 times

What they found surprised them: agoutis (Dasyprocta punctata), a widespread South American rodent species, dug up the seeds of the black palm and, instead of eating them, moved them to another location and re-buried them. One seed they tracked was moved 36 times over 209 days, travelling 749 meters and ending up 280 meters from where it began, according to a study published in the Proceedings of the National Academy of Sciences.

From the National Science Foundation in the USA:

Thieving Rodents: Did They Save Tropical Trees?

Rodents may have taken over seed-dispersal role of now-extinct mammals.

Big seeds produced by tropical trees such as black palms were probably once ingested and then left whole by huge mammals called gomphotheres.

Gomphotheres weighed more than a ton and dispersed the seeds over large distances.

But these Neotropical creatures disappeared more than 10,000 years ago. So why aren’t large-seeded plants also extinct?

A paper published this week in the journal Proceedings of the National Academy of Sciences (PNAS) suggests that rodents may have taken over the seed-dispersal role of gomphotheres.

“The question has been: how did a tree like the black palm manage to survive for 10,000 years, if its seed-dispersers are extinct?” asks Roland Kays, co-author of the paper and a zoologist at North Carolina State University and the North Carolina Museum of Natural Sciences.

“This research solves a long standing puzzle in ecology,” says Alan Tessier, program director in the National Science Foundation’s (NSF) Division of Environmental Biology, which funded the research.

“How did plant species that seem to be dependent on Pleistocene megafauna for seed-dispersal survive the extinction of that megafauna?”

Now, says Kays, scientists may have an answer.

By attaching tiny radio transmitters to more than 400 seeds, Patrick Jansen, a scientist at the Smithsonian Tropical Research Institute (STRI) and Wageningen University and colleagues found that 85 percent of the seeds were buried in caches by agoutis, common rodents in tropical lowlands.

Agoutis carry seeds around in their mouths and bury them for times when food is scarce.

Radio-tracking revealed a surprising finding: when the rodents dig up the seeds, they usually don’t eat them, but instead move them to a new site and bury them, often many times.

One seed in the study was moved 36 times.

Researchers used remote cameras to catch the animals digging up cached seeds. They discovered that frequent seed movement primarily was caused by animals stealing seeds from one another.

Ultimately, 35 percent of the seeds ended up more than 100 meters from their origin. “Agoutis moved seeds at a scale that none of us had ever imagined,” says Jansen.

“We had observed seeds being moved and buried up to five times, but in this system it seems that re-caching behavior is ‘on steroids,’” says Ben Hirsch of STRI and Ohio State University.

“By radio-tagging the seeds, we were able to track them as they were moved by agoutis, find out if they were taken up into trees by squirrels, then discover the seeds inside spiny rat burrows.

“That allowed us to gain a much better understanding of how each rodent species affects seed dispersal and survival.”

By taking over the role of Pleistocene mammals in dispersing large seeds, thieving, scatter-hoarding agoutis may have saved several species of trees from extinction.

See also here. And here.