Deforestaton is propeling fast changes in evolution, a study of the Brazilian rain forest suggests.

Researchers found that in areas where populations of large-billed, fruit-eating birds, such as toucans, have been driven out because of deforestation, palm trees have evolved to produce smaller and less successful seeds.

The Brazilian scientists collected more than 9,000 seeds from 22 palm populations in patches of rain forest that had been fragmented by coffee and sugar cane development during the 1800s.

Using evolutionary models and genetic data, the team correlated the small seed size with the absence of large, seed-dispersing birds. That measure correlates with successful germination, according to the scientists, whose work appears Friday in the journal Science.


“Unfortunately, the effect we document in our work is probably not an isolated case,” said Mauro Galetti from Sao Paulo State University in Sao Paulo, Brazil, who led the international research team.

The palms depend on fruit-eating birds to disperse the seeds, and only larger-billed species of such birds, such as toucans and cotingas, can consume the fruit and drop the seeds over large distances, according to the study. Fruit that drops near the tree often fails to lead to successful seed germination. Fruit dropped with pulp intact, usually by smaller birds, likewise does not lead to as much germination.

The researchers estimated how many generations it would take to produce the measured changes in seed size, and found it could occur within 100 years – a relative eye-blink in the time scale of naturally driven evolution.