How the Amazon became a biodiversity hotspot

The Amazon rainforest is a unique biodiversity hotspot, home to an astonishing array of plants and animals found nowhere else on Earth. Many of these species are restricted to specific regions, but the reasons behind this have long puzzled scientists. 

Now, a new international study, led by the UK Center for Ecology & Hydrology (UKCEH), offers fresh insights into the Amazon’s evolution during the last Ice Age, between 2.6 million and 11,700 years ago.

Fragile ecosystems of the Amazon

The research challenges long-standing beliefs about how the Amazon rainforest responded to climatic changes during the Ice Age. 

The findings suggest that the Amazon is far more sensitive to environmental fluctuations than previously thought, providing yet another reminder of the dangers posed by rapid, human-induced climate change and large-scale land use shifts.

Interconnected refuge for specialized species

For years, scientists have debated whether, during the Ice Age, the Amazon was divided into isolated “forest islands” known as refugia, or whether the forest remained continuous, similar to its current expanse. 

The UKCEH-led study, published in npj Biodiversity, offers a new perspective: while forest islands existed, they were connected by woodlands and savannas. This allowed certain adaptable animals to move between different habitats, while acting as a barrier for more specialized species that rely on specific ecosystems.

Biodiversity of the Amazon

The vegetation and climate of a region play a key role in natural evolution. As environmental conditions changed, animals across the Amazon adapted, leading to the emergence of new species in different areas. This process explains why the Amazon hosts such a diverse range of life today.

“Climate changes in the past played a huge role in shaping how the Amazon forest looked and where it grew. Similar changes are coming very soon and much faster,” said lead author Douglas Kelley, a land surface modeler at UKCEH. 

“Previously, fluctuations in climate took thousands of years to happen, enabling plants and animals to adapt, but now significant global warming is happening within decades due to increasing human-driven greenhouse gas emissions.”

The research team included scientists from institutions such as the Ontario Forest Research Institute, Kiel University in Germany, the UK’s Met Office, and the Field Museum of Natural History in Chicago. 

Amazon biodiversity of the Ice Age 

By combining advanced climate and vegetation modeling with fossilized pollen records from sediment, the experts were able to create detailed predictions of the types of plants that thrived in the Amazon during the Ice Age. Previous research had largely relied on single techniques, but this study incorporated a broader range of data and methods.

Crucially, the researchers considered the gaps between areas where fossilized pollen has been found and analyzed whether animals could have moved between these habitats. 

Computer and statistical models predicted what types of vegetation likely existed in these in-between areas, verifying the team’s predictions with the plant types recorded in adjacent regions.

During the Ice Age, the Amazon’s forest cover was dramatically reduced due to the colder, drier climate. Lower levels of carbon dioxide in the atmosphere, along with dry conditions, limited tree growth and led to more frequent wildfires, which destroyed large portions of the forest.

Innovative nature of the research 

Study co-author Dr. Hiromitsu Sato of the Ontario Forest Research Institute highlighted the innovative nature of the team’s approach. 

“We believe our study, involving integrated modeling methods, provides the best evidence to date on the origins of the rich biodiversity in the Amazon,” said Dr. Sato.

“Using land surface modeling to provide crucial information on biodiversity is a new and very exciting innovation that could be used in future to investigate the history of species where there is a shortage of data.”

Understanding Amazon diversity of the past

Looking ahead, the researchers plan to explore how various groups of Amazonian species – such as monkeys, frogs, antbirds, butterflies, and lianas – diverged over thousands of years in response to changing environments. 

By continuing to investigate the intricate relationship between climate, vegetation, and species evolution, the team hopes to gain a deeper understanding of the Amazon’s past – and how this knowledge can inform efforts to protect its future in the face of ongoing environmental challenges.

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