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Sky islands

Flickering sky islands
generate Andean biodiversity

June 19, 2019

Colombian Andes

Giving rise to the richest alpine flora in the world, interconnections between islands of Andean paramo vegetation flicker off and on as global temperatures rise and fall during the last million years

A new video shows how climate change connected and disconnected Andean “sky islands” during the past million years. The innovative mathematical model used to make the video was based on fossil pollen records and shows how the entire páramo habitat shifted. The model can predict climate change effects in mountainous regions around the world, according to an international team of scientists including authors from STRI.

The páramo is an other-worldly habitat of stunted shrubs and alpine plants specially adapted to high winds, cold temperatures, poor nutrients and limited moisture. It exists in between the upper forest line, where trees dominate, and the snowline.

“Páramo habitat crept up and down mountain slopes, driven by dry glacial periods alternated with warmer, humid interglacial periods,” said Suzette Flantua, former STRI postdoctoral fellow, now at the University of Bergen, Norway. “Our model reconstructs the connectedness of páramo habitats in the hopes that it will give us a way to see how dynamic this system had been, and to test how and why new species evolved not only in the Andes but in mountainous regions everywhere.”

New species result when animals or plants are isolated and their characteristics change in such a way that their descendants can no longer interbreed.

To visualize how páramo shifted in the past, researchers looked to a unique fossil record from Funza, Colombia. By driving a 100 meter-long drill pipe into ancient sediments, scientists extracted fossil plant pollen trapped there, revealing the migration of the forest line as temperatures changed during a million years.

As the average temperature at Funza fluctuated between 6 and 15 degrees Celsius, the forest line shifted between 1,900 to 3,500 meters above sea level.

During extremely cool global ice ages, temperatures in the Andes were 8 degrees Celsius cooler than today. Glaciers spread down mountainsides, pushing the páramos to lower elevations where they connected with páramo “islands” from other mountains.

“As the temperature changed we calculated how likely it was for each island of vegetation to connect to neighboring islands,” Flantua said. “The unique aspect of this model is that we did that for an entire 1 million-year period producing a continuous curve of merging and mixing páramos.”

The team used geographical information systems (ESRI ArcGIS 10.3) and specialized software for estimating connectivity (Gnarly Landscape Utilities, Linkage mapper and Conefor) to reconstruct the likelihood of dispersal and migration of plants and animals between páramo islands even when islands were not yet physically attached to each other.

"What we see in the Andes today is far from ‘normal’ in their evolutionary past” said co-author Aaron O'Dea, STRI staff scientist. “This model shows that the paramo exist near their elevational limits. As the world warms, the paramó will be pushed ever upwards until there is no more space. They could eventually be snuffed out, along with their unique birds, frogs, butterflies and plants.”

The authors received funding from the Netherlands Organization for Scientific Research, the Hugo de Vries Foundation, Panama’s Sistema Nacional de Investigadores de SENACYT, the German Centre for Integrative Biodiversity Research and NUFFIC, a Dutch organization for internationalization in education.

As temperature fluctuates, the area of unique páramo vegetation on mountain summits shifts up and down. By using fossil pollen to track the páramos over a million years, researchers show that páramos today are close to their historical limits and threatened by rising temperatures. Artwork by Catalina Giraldo Pastrana in collaboration with Suzette Flantua and Henry Hooghiemstra.
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