Rainforest Deforestation Yields Smaller Seeds: Rapid Evolution in Brazil

It turns out that the deforestation of the Brazilian rainforest has more impacts than we thought. Scientists have discovered that in areas that have been impacted by humans, palm tree seeds have evolved to be far smaller than their undisturbed counterparts.

Brazil's Atlantic rainforest was once home to a vibrant array of plants and animals, boasting rare species such as black-faced lion tamarins, blonde capuchin, toucans, cotingas and maned sloths. Yet with the arrival of sugar and coffee plantations, this forest was put into jeopardy. Parts of the forest were rapidly destroyed and today, just 12 percent of the original forest remains, according to BBC News.

In order to find out what this impact might have on seeds and species of plants, the researchers examined 9,000 seeds collected from palm trees throughout the rainforest. They found that, surprisingly, seeds were far smaller in areas that had been disturbed by humans. In fact, seed sizes ranged from about .3 to .4 inches in diameter. That's a huge contrast to areas where little impact has occurred and where seeds can reach .55 inches in diameter or larger, according to LiveScience.

So why the smaller seeds? It turns out that it's not about stressed trees; it's more about evolution. In areas where the rainforest has been disturbed, there are far less large, seed-dispersing birds such as the toucan and the cotinga. Instead, smaller species are left behind, like the thrush. Because these trees aren't receiving the benefit of seed dispersal from these large species they're evolving rapidly to produce smaller seeds.

"Unfortunately, the smaller seed size also means a lower probability for successful recruitment in the forest," said Pedro Jordano of the Donana Biological Station in an interview with BBC News. "Smaller seeds are less likely to germinate, they are prone to losses by desiccation and they are more quickly attacked by fungi."

The researchers weren't done yet, though. They then used genetic data from the seeds and created computer models to see how fast these trees may have evolved. After examining the data, they found that it would take 50 to 75 years for the changes to occur--relatively fast in terms of evolution.

The findings show a disturbing phenomenon occurring in the Atlantic rainforest. But it's likely that this research isn't only applicable to the one forest; it's very likely that the same scenario is occurring throughout the rainforests of the world. The only way to stop the issue is by conservation and tree planting.

The findings are published in the journal Science.