18. September 2019

An answer to the hitherto unsolved riddle about animal species’ exhibition pattern may be found in the mountains

Since the 19th century, when world explorers and scientists first began to examine and document the Earth’s biodiversity, researchers have tried to find answers to what exactly makes the species’ patterns of distribution the way they are. But without luck. Two articles in the scientific journal Science now give a series of answers but might also give birth to whole new questions. The articles show that biological diversity is surprisingly large in tropical mountain areas. In charge of the two articles is a team of researchers from the DNRF’s Center for Macroecology, Evolution and Climate (CMEC) at the University of Copenhagen.

The volcano Chimborazo at the Andes in Ecuador. The volcano is especially known as the motive in Homboldts' famous drawing of the volcano's plant zones.
The volcano Chimborazo at the Andes in Ecuador. The volcano is especially known as the motive in Homboldts’ famous drawing of the volcano’s plant zones. Photo: Spyros Theodoridis

Through the 19th century, Alexander von Humboldt, Charles Darwin, and Alfred Russel Wallace were some of the world explorers who tried to solve the riddle about what circumstances and relationships regulated and determined the distribution of biodiversity on Earth. Ever since, two centuries of research have equally tried to find a satisfying answer to this question but without luck.

Now, two articles recently published in the scientific journal Science give a series of answers but, at the same time, also further contribute to the mystery. The results show that the most diverse biodiversity is not where it was hitherto thought to be, but instead, in areas with tropical mountains. Although mountain regions cover only 25% of Earth’s land area, they are home to more than 85% of the world’s species of amphibians, birds, and mammals, and many of these are found only in mountains.

“The challenge is that, although it is evident that much of the global variation in biodiversity is so clearly driven by the extraordinary richness of tropical mountain regions, it is this very richness that current biodiversity models, based on contemporary climate, cannot explain: mountains are simply too rich in species, and we are falling short of explaining global hotspots of biodiversity,” said Professor Carsten Rahbek, lead author of both review papers published in Science and head of center at CMEC.

The surprisingly rich biodiversity in the mountains has two main sources. First, the climate in the mountains is much more complex and diverse than in the nearby areas of lowland. This complexity and rich combination can play a central role in both the occurrence of new species and the survival of old species through times with extreme climate changes.

“People often think of mountain climates as bleak and harsh,” said study co-leader Michael K. Borregaard, an assistant professor at CMEC. “But the most species-rich mountain region in the world, the Northern Andes, captures, for example, roughly half of the world’s climate types in a relatively small region—much more than is captured in the nearby Amazon, a region that is more than 12 times larger.”

Another part of the explanation is the interaction between geological processes at the formation of the mountains and the complex ways in which the climate changes both locally and throughout time. This gives the evolution of species a great latitude.

“The global pattern of biodiversity shows that mountain biodiversity exhibits a visible signature of past evolutionary processes. Mountains, with their uniquely complex environments and geology, have allowed the continued persistence of ancient species deeply rooted in the tree of life, as well as being cradles where new species have arisen at a much higher rate than in lowland areas, even in areas as amazingly biodiverse as the Amazonian rainforest,” said Professor Rahbek.

The results are based on a massive collection process whereby the research team gathered data and mapped the biodiversity in every mountain area in the world. Then, the researchers brought together all of the material in an interdisciplinary field ranging from macroecology and evolutionary biology to the sciences of geology.

Tribute to Humboldt

The two articles are part of the journal’s celebration of Alexander von Humboldt’s 250th birthday. In 1799, Humboldt went on a five-year-long scientific discovery during which he wandered 8000 kilometers through Central America and South America. During his journey, he traveled to the Andes Mountains and became one of the first people to establish the study of biodiversity in mountains.

“Our papers in Science are a testimony to the work of von Humboldt, which truly revolutionized our thinking about the processes that determine the distribution of life. Our work today stands on the shoulders of his work, done centuries ago, and follows his approach of integrating data and knowledge of different scientific disciplines into a more holistic understanding of the natural world.  It is our small contribution of respect to the legacy of von Humboldt,” said Professor Rahbek.


Read one of the two scientific articles in Science here

The other Science article can be found here

Further information about the study can be found in a press release from the University of Copenhagen here

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