When big birds disappear, palm seeds get smaller

As toucans and other large-beaked birds have vanished from Brazilian forests, the seeds of palm trees have shrunk, scientists report.

The palm tree Euterpe edulis needs birds to help spread its seeds. Large fruit-eating birds can eat and disperse big seeds, but they’re also more likely than smaller birds to go extinct when forests are broken up.

The researchers examined 22 populations of palms in Brazil and found that seeds were smaller in areas where big birds had largely disappeared. Small birds such as thrushes ate about one-third of the fruit in well-preserved forests but as much as 98 percent in areas without many large birds. Experiments and field observations also suggested that thrushes couldn’t disperse seeds more than 12 millimeters wide.

The changes in seed size could have taken place within 75 years of losing the large-beaked birds, the authors estimate in Science. The shift could be bad news for the forest: Small palm seeds are less tolerant of drought, and the plants that grow from them tend to be smaller too. — Roberta Kwok | 31 May 2013

Source: Galetti, M. et al. 2013. Functional extinction of birds drives rapid evolutionary changes in seed size. Science doi: 10.1126/science.1233774.

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