Amazon biodiversity older than believed

Jeremy Hance
November 11, 2010

A new study in Science has found that the incredible biodiversity of the Amazon rainforest goes back much further than expected, perhaps upending old ideas about how the Amazon basin became arguably the world's most biodiverse ecosystem. According to the study, the origin of rich biodiversity in the Amazon likely goes back more than 20 million years when the Andean mountains were rising.

"The Andean mountain building profoundly affected the diversity and evolution of the Amazonian biota. It would be difficult to name any major group of Amazonian plants or animals whose fate had not been touched in some way by the formation of the vast Andean mountain chain," William Laurance, a conservation biologist at James Cook University who has spent decades working in the tropics, told mongabay.com. Laurance was not involved with the study.

By comparing biodiversity patterns today with geological and molecular datasets, researchers found that the highest diversity of species were in a region spanning over a million square kilometers which originated with the rising Andes. Given this, the authors believe they have found a strict the connection between the rich diversity Amazon rainforests and the rise of the Andes over 20 million years ago.

Andes mountains in Peru. Photo by: Rhett A. Butler.
The researchers also note that as Andes rose they created a vast wetland appeared in the Amazonian region. This wetland also played a role. Around 10 million years ago when the Amazon River was formed, the wetland dried up, making way for the colonization of new plants and animals.

"This research is very important in the sense of understanding the historical forces that have shaped the world’s largest and most biologically diverse rainforest," explains Laurance. "Many mysteries remain in Amazonia, but it’s becoming clear that geological events such as the Andean uplift and shifts in the courses of major rivers have had a profound influence on the biogeography of the region. These ideas are replacing the rather simplistic Pleistocene 'refugia' or 'species pump' ideas that were formerly in vogue. Today, however, we know that most species in Amazonia are considerably more ancient than the Pleistocene, which began only 2 million years ago."

The study points to the fact that species richness in the Amazon was already very high before the Pleistocene. In fact, for plants and reptiles, diversity was even higher pre-Pleistocene than it is today.

Laurance described the study as "a very nice synthesis of knowledge from disparate fields, with evidence drawn from geomorphology, paleontology, biogeography, and evolutionary genetics."

CITATION: C. Hoorn, F.P. Wesselingh, H. ter Steege, M.A. Bermudez, A. Mora, J. Sevink, I. Sanmartín, A. Sanchez-Meseguer, C. L. Anderson, J.P. Figueiredo, C. Jaramillo, D. Riff, F.R. Negri, H. Hooghiemstra, J. Lundberg, T. Stadler, T. Sarkinen, A. Antonelli: ‘Amazonia through time: Andean uplift, climate change, landscape evolution and biodiversity. Science (12th of November, 2010).

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Jeremy Hance
mongabay.com (November 11, 2010).

Amazon biodiversity older than believed.