Geologically vibrant continents produce higher biodiversity

Date:
September 28, 2021
Source:
ETH Zurich
Summary:
Using a new mechanistic model of evolution on Earth, researchers can
now better explain why the rainforests of Africa are home to fewer
species than the tropical forests of South America and Southeast
Asia. The key to high species diversity lies in how dynamically
the continents have evolved over time.



FULL STORY ========================================================================== Tropical rainforests are the most biodiverse habitats on Earth. They
are home to a huge number of different plants, animals, fungi and other organisms. These forests are primarily spread over three continents, concentrated in the Amazon Basin in South America, the Congo Basin in
Central Africa, and the vast archipelago of Southeast Asia.


==========================================================================
One might assume that all tropical rainforests are about equally diverse
due to their stable warm and humid climate and their geographical location around the equator -- but this is not the case. Compared to South America
and Southeast Asia, the number of species in Africa's humid tropical
forests is significantly lower for many groups of organisms.

Palms with few species A good illustration of this uneven distribution --
what researchers refer to as the pantropical diversity disparity (PDD)
-- is palm trees: of the 2,500 species worldwide, 1,200 occur in the
Southeast Asian region and 800 in the tropical forests of South America,
but only 66 in African rainforests.

Why this should be so is debated among biodiversity researchers. There is
some evidence that the current climate is the cause of the lower species diversity in Africa's tropical forests. The climate in Africa's tropical
belt is drier and cooler than that in Southeast Asia and South America.

Other evidence suggests that the different environmental and tectonic
histories of the three tropical forest regions over tens of millions
of years had an impact on the differing levels of biodiversity. Such environmental changes include, for example, the formation of mountains, islands, or arid and desert areas.



========================================================================== However, it is difficult to distinguish between the two factors of
current climate and environmental history.

Mountain building brings up diversity Led by Loi"c Pellissier, Professor
of Landscape Ecology, researchers at ETH Zurich have now investigated
this question with the help of a new computer model that allows them to simulate species diversification over millions of years of evolution. They conclude that the current climate is not the main reason why biodiversity
is lower in the rainforests of Africa. Rather, biodiversity has emerged
from the dynamics of mountain building and climate change. The results
of the historical simulations largely coincide with the patterns of biodiversity distribution observable today.

"Our model confirms that differences in palaeoenvironmental dynamics
produced the uneven distribution of biodiversity, rather than current
climatic factors," says Pellissier. "Geological processes as well as
global temperature fluctuations determine where and when species emerge or
go extinct." One factor in particular is crucial to high biodiversity
on a continent: geological dynamics. Active plate tectonics promote
both the formation of mountains, such as the Andes in South America,
and the emergence of archipelagos, as in Southeast Asia. These two
processes result in many new ecological niches, which in turn give rise
to numerous new species. Africa's rainforest belt, on the other hand,
has had less tectonic activity over the past 110 million years. It is
also relatively small because it is bordered by drylands in the north and south, limiting its spread. "Species from humid regions can hardly adapt
to the dry conditions of the surrounding drylands," Pellissier points out.



========================================================================== Geologically vibrant continents produce higher biodiversity The "gen3sis"
model developed by ETH researchers was only recently presented in the
journal PLoS Biology. It is a mechanistic model in which the primary constraints such as geology and climate are represented together
with biological mechanisms and from which biodiversity patterns can materialise. To simulate the emergence of biodiversity, the most important processes to integrate into the model are ecology (i.e. each species has
its own limited ecological niche), evolution, speciation and dispersal.

"With these four basic rules, we can simulate the population dynamic of organisms over shifting environmental conditions and offer a very good explanation for how the organisms came about," Pellissier says.

By building their model on these basic evolutionary mechanisms, the
researchers can simulate species diversity without having to input (distribution) data for each individual species. However, the model
requires data on the geological dynamics of the continents under
consideration, as well as humidity and temperatures from climate reconstructions.

The researchers are now refining the model and running simulations to understand the emergence of biodiversity in other species-rich regions,
such as the mountains of western China. The model's code and the palaeoenvironmental reconstructions are open source. All interested evolutionary and biodiversity researchers can use it to study the
formation of biodiversity in different regions of the world.

========================================================================== Story Source: Materials provided by ETH_Zurich. Original written by
Peter Ru"egg. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Oskar Hagen, Benjamin Flu"ck, Fabian Fopp, Juliano S. Cabral,
Florian
Hartig, Mikael Pontarp, Thiago F. Rangel, Loi"c Pellissier. gen3sis:
A general engine for eco-evolutionary simulations of the processes
that shape Earth's biodiversity. PLOS Biology, 2021; 19 (7):
e3001340 DOI: 10.1371/journal.pbio.3001340 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210928074954.htm

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