Why mountains are biodiversity hotspots

A pairing of two new studies reveal why mountains — tropical mountains, specifically — are so biologically diverse compared to other regions on Earth. While in the process of conducting these studies, scientists realized the high levels of biodiversity on mountains is far greater than what they expected.

“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 lead author of both studies Professor Carsten Rahbek.

Scientists from the Center for Macroecology, Evolution and Climate (CMEC) and the GLOBE Institute of the University of Copenhagen synthesized data from several different fields including macroecology, evolutionary biology, earth sciences, and geology to gain a firmer grasp on why mountains are so rich in biodiversity.

They found that the climate of rugged tropical mountain regions is different than that of lowland regions in terms of complexity and diversity.

“People often think of mountain climates as bleak and harsh,” said study co-leader Michael K. Borregaard. “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 nearby Amazon, a region that is more than 12 times larger.”

“Tropical mountains, based in fertile and wet equatorial lowlands and extending into climatic conditions superficially similar to those found in the Arctic, span a gradient of annual mean temperatures over just a few km as large as that found over 10,000 km from the tropical lowlands at Equator to the arctic regions at the poles,” Borregaard added. “It’s pretty amazing if you think about it.”

Furthermore, the team found that high biodiversity is also connected to the geological dynaimcis, which interact with complex climate changes over time, of mountain building. These geological dynamics allow for evolutionary processes to take place. 

“The global pattern of biodiversity shows that mountain biodiversity exhibits a visible signature of past evolutionary processes,” said Rahbek. “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.”

The interaction between geology and biology may also contribute to mountain biodiversity richness. The researchers found that high diversity in most tropical mountains is tightly linked to bedrock geology — especially those mountains containing ancient oceanic crust. Therefore, the researchers hypothesize that tropical mountains, with soil originating from oceanic bedrock, provide exceptional environmental conditions that help plants to adapt and change more easily than locations elsewhere.

And these plant adaptations may, in turn, drive speciation cascades, in which the speciation of one group leads to the speciation of another group, therefore affecting animal life and overall biodiversity.

These two papers are published in Science.

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By Olivia Harvey, Earth.com Staff Writer

Image Credit: Jesper Sonne/CMEC