Hidden 'Highways' Allow Species to Travel Between Brazil's Rainforests

For a long time, scientists believed that tree migration between the Amazon and Atlantic forests occurred only during wetter climatic periods, when much of South America was covered in rainforest. However, the findings from a recent study, led by the Royal Botanic Garden Edinburgh (RBGE) and the University of Exeter, offer a new perspective.

"Rather than tree species being exchanged during specific wetter periods in the past, we found that species have dispersed consistently over time," said Dr. James Nicholls of RBGE. "This probably happens slowly, by generations of trees growing along the 'highways' provided by rivers that run through Brazil's dry ecosystems."

The research team, which also included scientists from Brazil, focused on 164 species of Inga trees, which are common across Latin American rainforests. By analyzing their DNA, the team reconstructed the trees' evolutionary history, determining when each species diverged from its ancestors. They also mapped the geographical spread of these species to study patterns of migration between the Amazon and Atlantic rainforests.

The researchers discovered 16 to 20 "dispersal events" in which species moved from the Amazon to the Atlantic forest and successfully established themselves. These events occurred throughout the evolutionary timeline of the Inga species, rather than just during wetter periods when rainforests were more widespread. In contrast, only one or two instances of species moving from the Atlantic to the Amazon were found. The scientists believe this imbalance may reflect the vast size of the Amazon, which generates more seed dispersal to surrounding areas.

The study highlights the critical role of riverside forests in maintaining ecological connections between the rainforests. These forests, which are protected by Brazilian law, are essential for ensuring the ongoing movement of species across the landscape.

Professor Toby Pennington, from Exeter's Department of Geography and the Global Systems Institute, and RBGE, commented, "This legal protection - and efforts to preserve these riverside forests - are highly valuable for long-term habitat connectivity."

He added, "The study also tells us something fundamental about the history of the incredible biodiversity of the Atlantic rainforest, which contains about 3,000 more plant species than the Brazilian Amazon. Only 20% of the Atlantic rainforest now remains intact. In the short term, we need to protect these precious rainforests. In the long term, our study shows that we must also conserve the connections between them."

The study was funded by the United States National Science Foundation.

Research Report:Continuous Colonization of the Atlantic Coastal Rainforests of South America from Amazonia