The unique high-elevation Andes grasslands ‘páramos’ have waxed and waned in size over time, driving biological radiations and pushing them to their limits under anthropogenic pressure. An international research team, led by Suzette Flantua and Henry Hooghiemstra from the University of Amsterdam, has now shed light on the dynamic history of this hyper-diverse alpine system providing insights into drivers of evolutionary hotspots. A research article has been published this week in a special Issue on Alexander von Humboldt in the Journal of Biogeography.
Páramos are alpine tundra grasslands in the high Andes which are essential for water regulation and carbon reservoirs. The history of the páramos was highly dynamic, and this instability likely lead to the páramos being the richest tropical alpine ecosystem in the world. Many recent studies have shown that speciation of plants and animals in the páramos accelerated in the last 3 million years – the period when the world dipped in and out of ice ages. How did the rapid climate fluctuations play out on the highly variable topography of the Andes, and what role did this play in determining the ecology and evolution of the unique páramos?
The published study builds a remarkable, million-year-long, reconstruction of the spatial distribution of the páramos based on a fossil pollen record in the highlands of Colombia. This unique record shows that as the global climate fluctuated, the páramos moved up and down the mountain slopes as the climate warmed and cooled respectively. This incredible migration of entire ecosystems led to the páramos becoming more isolated or coalescing into larger, conjoined, patches in a cyclical fashion.
By uniting climate and elevation models of the mountainous and complex northern Andes, the research team was able to quantify for the first time the degree of isolation and connectivity of páramos on the different mountain ranges through time. The results show that extreme cool and warm events were quite rare and short, and likely played a minimal role in driving the páramos’ evolutionary history. Intermediate, but highly variable temperatures, occurred much more frequently, and lasted much longer, and were therefore much more representative of conditions during the history of the páramos.
‘There is this stubborn idea that the tropics are highly stable environments and that this stability has facilitated the build-up of the characteristically high biodiversity we see in the tropics today. Our study suggests quite the opposite’, explains Suzette Flantua, former PhD candidate at the UvA Institute for Biodiversity and Ecosystem Dynamics (IBED). ‘These ecosystems were highly dynamic and still managed to accumulate extraordinary diversity. It could be that the changes were driving the formation of new species.’
The study resolves how the combined effect of temperature fluctuations and mountain topography resulted in a highly variable pattern of páramo connectivity – coined by the authors as the ‘flickering connectivity system’ – and that these patters differed among mountain ranges. ‘It is often said that the past is the key to the present, because it helps us understand how mountain ecosystems dealt with dramatic changes in climate’, describes senior IBED researcher Henry Hooghiemstra. ‘We already perceived that the páramos had gone through a quite dynamic past, but how it translated into connectivity changes over time had never been fully quantified’.
The findings have implications for understanding how biodiversity forms in mountain ranges. ‘The flickering connectivity system may explain why paramós are extremely species rich – comparable to tropical rainforests,’ says Renske Onstein, former postdoc at IBED. ‘The intermittent connection and disconnection of populations may have boosted the speciation process, resulting in spectacular plant diversification’.
The unique topography of each mountain range across the Northern Andes played a decisive role in shaping the degree of connectivity through time. It will take further work to reveal how that played out in an evolutionary landscape. Meanwhile, it is clear is that the páramos we see today in this warm period are close to their historical elevation limits. ‘This is an ecosystem that is literally living on the edge’ warns Aaron O’Dea from the Smithsonian Tropical Research Institute, in Panama. ‘Humans have already slashed the páramos distribution through fire and grazing, and now, as the world warms, páramos will be pushed upwards into smaller patches. Without protection, the páramos and their irreplaceable diversity will be snuffed out’.
The article is accompanied by a 3D animation. The video mainly shows this flickering connectivity system as described in the paper and has been widely distributed among social media, with almost 1000 views on YouTube already. The maker of the video proudly describes the process of integrating digital art and scientific theories: ‘It was actually much more difficult than I had imagined’, chuckles Colombian science artist Catalina Giraldo. ‘Scientists have a vision in their mind on how they understand the system but this might not be very clear for the general audiences. In the end, the biggest challenge is to make it enjoyable, interesting and easy to understand’.
Suzette Flantua, Aaron O’Dea, Renske E. Onstein, Catalina Giraldo, Henry Hooghiemstra 2019. The flickering connectivity system of the northern Andes. Journal of Biogeography. DOI: 10.1111/jbi.13607
The scientific work was financially supported by NWO and the video by the Hugo de Vries foundation, Amsterdam.