Simulating the Evolution of Life in South America

Modeling the ecology and evolution of biodiversity: Biogeographical cradles, museums, and graves (2018) Rangel et al., Science, 244, DOI: 10.1126/science.aar5452

The Crux

Understanding the processes which drive biodiversity worldwide is never more crucial than now, in a world where biodiversity is shrinking rapidly. Biogeography, the study of species distributions, has come a long way, but there are still a lot of problems that need solving, including improving our understanding of the interactions between factors like climate change, dispersal abilities, fragmentation and species competition, to name a few.

This paper attempted to analyse some of the effects of those factors in concert, by producing a simulation of the evolutionary process in the world’s most biologically diverse continent, South America.

What They Did

South America was chosen not only for its biodiversity, but for its place as the home of the Andes, a mountain range which is not only a huge source of climatic variation, but a huge dispersal barrier for many species.

The researchers simulated everything to do with a species life history over an 800,000 year period. This included for instance whether or not its dispersal ability allowed it to survive habitat fragmentation, or whether it was able to evolve fast enough to survive climatic changes.  The simulation used no ‘real’ data whatsoever, instead the parameters used to run the simulation were randomised based on biogeographical principles. The simulations were also run over a gradually topographically smoothed version of South America, which emphasised the effect that the wide variations in climate produced by the Andes have on increasing species diversity.

Did You Know: Islands in the Tropics

Island biogeography studies the distributions of species on islands, which often show trends in species richness and composition that vary wildly from the mainland. However many of the trends seen in islands can also be seen in mountain areas, as species which require higher altitudes to exist face the same issues dispersing between areas of similar altitude as do species attempting to move from island to island. Cool mountain forests in the otherwise dry Great Basin in the USA and the higher, less tropical peaks of the Anders are great examples of this, with many species isolated in these mountaintops.

What They Found

The simulations bore a strong resemblance to current species patterns in South America, lending credibility to these results. The simulations were most sensitive to the location of the ‘founder species’, with the effect of temperature, speciation and extinction on a species varying depending on where it first appeared. The species ability to evolve quickly also affected the models, with high rates of evolution promoting the dominance of relatively few species, and low rates producing high extinction. Overall species diversity declined as the topographical variation of the Andes was reduced, confirming the role of a varied climate as a driver of species diversity.

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Increasing rates of evolution in the simulations prevented high levels of species extinctions, but increasing them too much resulted in a few species dominating the rest (Image Credit: Santiago Ron, CC BY-ND 2.0)

Problems

Whilst this paper is undoubtedly cool, I want more information on its application to species fluctuations today. Is something that doesn’t take into account the rapid human-driven change we’re seeing today useful in predicting species distributions in such an immediate future?

So What?

Models like this are frankly astonishing. They give hope that one day we won’t necessarily need mountains of data to provide simulated forecasts of the consequences of our immediate actions on the planet. Having seen co-author Carsten Rahbek speak on the challenges in modelling recently, I hope that advances in this field will help us isolate regions and species in dire need of conservation.

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