May 30, 2013 — The disappearance of large, fruit-eating birds from tropical forests in Brazil has caused the region's forest palms to produce smaller, less successful seeds over the past century, researchers say. The findings provide evidence that human activity can trigger fast-paced evolutionary changes in natural populations.
Mauro Galetti from the Universidade Estadual Paulista in São Paulo, Brazil, along with an international team of colleagues, used patches of rainforest that had been fragmented by coffee and sugar cane development during the 1800's to set up their natural experiment. They collected more than 9,000 seeds from 22 different Euterpe edulis palm populations and used a combination of statistics, genetics and evolutionary models to determine that the absence of large, seed-dispersing birds in the area was the main reason for the observed decrease in the palm's seed size.
The study appears in the 31 May issue of the journal Science.
"Unfortunately, the effect we document in our work is probably not an isolated case," said Galetti. "The pervasive, fast-paced extirpation of large vertebrates in their natural habitats is very likely causing unprecedented changes in the evolutionary trajectories of many tropical species."
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