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Rescuing Tropical Trees from Extinction

NSF Award:

DEB (Ecology): Seed Dispersal by Central American Agoutis - A Mutualism Conditioned by Predators or Food?  (New York State Education Department)

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Rodents may be responsible for the survival of tropical trees after large mammals became extinct 10,000 years ago. Researchers from North Carolina State University, the North Carolina Museum of Natural Sciences and the Smithsonian Tropical Research Institute used novel techniques to show that the agouti--a guinea pig-like mammal--became tropical tree seed bearers and may have transported the seeds long distances to escape competition and foster new populations.

The new methods used to track seed movements and determine seed fate provide some of the first data on long-term seed dispersal and survivorship. This new information will enhance our understanding of how plants adapt to shifting habitats and climate change.

When large mammals--those weighing a metric ton--walked the earth, they ate fruits produced by tropical plants and then passed the seeds whole through their digestive systems as they travelled. The seeds germinated and grew far enough away from their parent plant to avoid direct competition. Smaller animals, including the agouti, continued to inhabit the region after the large mammal extinctions. Initially, researchers hypothesized that these mammals either destroyed the seeds by eating them, or were unable to transport the seeds far enough away to promote survival.

In this new study, Patrick Jansen and colleagues tagged individual agoutis and used video surveillance to determine which animals were creating and robbing seed caches. They also tracked individual seeds as the agoutis moved them from one cache to another. The ability to monitor at the seed level, the agouti level, and the forest level allowed for a more comprehensive picture of this relationship.

The research team found that agoutis disperse palm tree seeds in a complex, step-wise manner: burying a seed, then digging it up and moving it to another site, over and over again. Ultimately, agoutis carried seeds to areas with 36 percent lower palm density than their original locations, greatly promoting seed survival. The agoutis also benefited from the transfer: Other agoutis were less likely to steal seeds buried in areas with fewer palm trees.

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  • researchers attach transmitters to seeds to track movement
Transmitters attach to seeds with specialized thread.
Patricia Kernan

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