Brazil is a paradise for birds; the country has more than 1,700 species. Among them is the colorful toucan, a bird with an almost comically giant bill that can be half as long as its body. There are lots of different types of toucan — red-breasted, channel-billed, keel-billed, saffron toucanet — each with its own color-scheme and distinctive call.
Unfortunately, as more humans have moved into Brazil's Atlantic coastal forests, the increase in hunting, logging and farming has taken a toll on the number of toucans. Now scientists have discovered that the drop-off in birds is reshaping the forest as well.
According to research published this week in the journal Science, here's what happened: The forest's dominant palm tree, called the jucara (Euterpe edulis), depends on birds to eat its fruit and then defecate the seed in a place where it can germinate and grow to become a new tree. According to Mauro Galetti, a biologist at the Estadual Paulista University in Brazil who studies the process, the toucans give jucara palms with large seeds a reproductive edge.
"These large birds, they have an extremely important role in the forest," Galetti says, "not only because they disperse seeds, but because they disperse large seeds."
The largest palm seeds — some the size of marbles inside a thin-skinned fruit — are too big for most birds, except for those big-mouthed toucans. So as the toucans disappeared, the palms that made big seeds were out of luck — no seed dispersers. Meanwhile, jucara trees that were genetically predisposed to make small seeds did just fine. In fact, they thrived and started to dominate the forest.
"The extinction of large birds changed the evolution of this palm," Galetti says. His team checked other possible causes of evolutionary change — shifts in soil fertility or rainfall, or in other seed dispersers. But the genetic change in the palm populations occurred most often where the toucans were scarcest.
Now, humans have always been messing with nature. When we cut down forests or prairie or when we overhunt, we change a region's mix of plants and animals. That's an "ecological" change, Galetti explains. But in this case, humans actually altered the genetic makeup of a wild palm tree population — in just a century, indirectly, and by accident.
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