Archaeologists to help uncover the origin of Amazonian biodiversity

Scientists will seek to reconstruct the distribution of species over the last thousand years. The study is part of project funded by the São Paulo Research Foundation, NSF and NASA.

By Elton Alisson

Agência FAPESP – Questions about the origin and the transformation of the Amazon’s megabiodiversity over millions of years have intrigued many biologists in different parts of the world. In an attempt to answer these questions, several hypotheses have been advanced over the last few decades. However, many of these hypotheses have not undergone scientific scrutiny due to a lack of paleoecological data and geomorphological evidence. Now, specialists from diverse areas – including paleoecology and archaeology – are investigating the topic. 

A group of international researchers, led by Brazilians and Americans, began a Thematic Project to reconstruct the origin and the distribution of organisms in the Amazon over the last 20 million years.

The project is funded by FAPESP and the National Science Foundation (NSF) under the auspices of an agreement that forges a partnership between the "Dimensions of Biodiversity" (NSF) and BIOTA-FAPESP programs. The study is also funded in part by the U.S. space agency, NASA.

“There is a great deal of interest among paleoecologists like such as myself – in the past, I studied ecology based on pollen fossils – in questions such as the origin of biodiversity in Amazonia, what happened in the forest during and after the Last Glacial Maximum [20,000 years ago], what changes emerged in the Middle Holocene [6,000 years ago] and whether the forest was untouched or a highly domesticated environment in the pre-Columbian eras [before 1492],” said Frank Mayle, professor at the University of Edinburgh, during a symposium entitled “The assembly and evolution of the Amazonian biota and its environment,” held at FAPESP’s headquarters in São Paulo.

Held on March 4, 2013, the event served as an initial meeting of researchers and project members and was open to the public. Then, from March 5 -8, specialists met at FAPESP behind closed doors to define the details of the research project.

According to Mayle, one of the hypotheses presented to explain the extensive Amazonian biodiversity was the “Refugial Hypothesis.” Proposed by the ornithologist and biogeographer Jürgen Haffer (1932-2010) in an article published in Science magazine in 1969, the theory asserted that some areas of the Amazon forest became dry during the glacial periods. Because of this, there would have been several forest fragments, separated from each other by savanna areas, that served as refuges for different animal populations.

During the period of geographic isolation (vicariance), these separated animal populations “without forest” evolved differently from each other, undergoing geographic speciation (allopatric). When the climate became humid again, forest vegetation grew up in the open regions, and the forest fragments were reconnected, allowing the ranges of the new species to be extended. 

This theory, however, could not be tested because of a lack of data. “The Refugial Hypothesis created a paradigm for biologists, but we lacked the paleoecological data and geomorphological proof required to test the hypothesis,” explained Mayle.

“The theory has not undergone scientific scrutiny, and today the majority of us do not give it much credit. Paul Colinvaux provided the first paleovegetation data from the Amazon basin in a 1996 article published in Science that contradicted the Refugial Hypothesis.

Colinvaux found indications of a continuously humid forest in an area that was thought to be a savanna during the Last Glacial Maximum, when the average temperature was five degrees colder than now. “This led many of us paleoecologists to infer that the Refugial Hypothesis was incorrect,” Mayle commented.

Open Questions

According to Mayle, it is still unknown what type of tropical forest that existed in the Amazon during the Last Glacial Maximum. To answer this question, efforts have been made to model the extents of the humid and dry forest at the time. The poor quality of the available data, however, represents one of the main stumbling blocks in clarifying this issue.

“The controversies about the Amazon during the Last Glacial Maximum resulted from the set of data that we have available,” commented Mayle. “There is little information; the challenge is to identify the spatial scale and the type of forest coverage that corresponds to the profile of older paleodata. This is why we are forced to make extrapolations and work with vegetation modeling.”

Another question that has preoccupied researchers is what happened in the Amazon during the Middle Holocene, when climatic conditions were much drier than in other periods and there was already a human presence and human activities (such as fire-making) in the region.

“Looking at what happened to the Amazon during the Holocene could give us an idea of what could happen in the region in the future,” Mayle said.

The most recent area of research interest, according to Mayle, is about land use in the region during the pre-Columbian period – an issue that involves both ecology and archaeology.

“It has been argued that when the Europeans reached the region, they found a virgin forest. However, there is archaeological data that shows that land use in the Amazon at the time was not limited to small-scale agriculture,” said Mayle.

“We see traces of land use in the Amazon in the Pre-Columbian period in French Guyana and Bolivia,” he stated. The researchers also want to know if the increase in human activity, fire and the use of economically important species for the region’s inhabitants in the Pre-Columbian period and the Holocene influenced the region’s biodiversity.

“We cannot rule out the hypothesis that part of the Amazon’s biodiversity could be related to anthropogenic factors [caused by human action],” he affirmed.

“When we talk about the percentage of the biota that is anthropogenic, it is difficult to distinguish which species occur naturally and which were economically important and emerged due to human presence. This is one of the reasons that we intend to work with archaeologists in this project to attempt to integrate different lines of evidence,” he explained.