The extraordinary biodiversity seen in the Amazon rainforest — one of the most species-rich ecosystems on Earth — may have evolved mainly due to the rise of the Andes. And it is older than earlier thought.
An international team of scientists, including a leading evolutionary biologist from the Academy of Natural Sciences, says that the origin of rich biodiversity in the Amazon likely goes back more than 20 million years when the Andean mountains were rising.
The findings of the study, which is based primarily on the work of Academy of Natural Sciences scientist Dr John Lundberg, have been published as a review article in this week's edition of Science.
The Amazon, the world's largest river basin, is home to the largest rainforest on Earth, covering about 8.2 million square kilometres in nine countries. This area, known as Amazonia, holds an amazing biodiversity of life, harbouring one in 10 known species in the world and one in five of all birds. The majority of the rainforest is in Brazil, followed by Peru, and smaller portions in Colombia, Venezuela, Ecuador, Bolivia, Guyana, Suriname and French Guiana.
By comparing current biodiversity patterns with geological and molecular datasets, the researchers found that the highest diversity of species were in a region spanning over a million square kilometres which originated with the rising Andes. This led the scientists to concur that they have found a strict connection between the development of the Amazon basin and the geological history of the Andes.
As Andes rose, they created a vast wetland which appeared in the Amazonian region. Around 10 million years ago when the Amazon river was formed, the wetland dried up, making way for the colonisation by new plants and animals.
Till now there had been innumerable theories on the origin and complexity of the present day biodiversity in the Amazonian region. Though many had believed that the Andes had influenced rainforest composition, no one had till date been able to ascertain when and how this had happened.
"The Amazonian region, from its highest mountains to immense lowland rivers, supports a tremendous biological richness of species," said Lundberg, curator and Chaplin chair of ichthyology at the Academy of Natural Sciences in Philadelphia. "Many previously unseen species are discovered and documented every year."
