Geologically vibrant continents produce higher biodiversity

Tropical rainforest in Laos, Southeast Asia - a region where geological dynamics led to very high biodiversity. (Picture: Picture: Oskar Hagen/iDiv)

Note for the media: Use of the pictures provided by iDiv is permitted for reports related to this media release only, and under the condition that credit is given to the picture originator.

New computer model helps to better understand species diversity in rainforests

Based on a media release from ETH Zurich

Leipzig, Zurich. Using a new mechanistic model of evolution on Earth, researchers at German Centre for Integrative Biodiversity Research (iDiv) and ETH Zurich 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.

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 is the case, is widely de­bated among biod­iversity re­search­ers”, explains co-author Dr Renske Onstein, Head of Junior Research Group Evolution and Adaptation at iDiv.

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

Researchers from iDiv and ETH Zurich have now investigated this question with the help of a new computer model called “gen3sis”. “The model allows us to simulate the evolution and diversification of species over many millions of years,“ explains Dr Oskar Hagen, who developed the model as part of his doctoral thesis which was supervised by Prof. Loïc Pellissier, Professor of Landscape Ecology at ETH Zurich. 

The researchers 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.

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.

New mechanistic approaches in biodiversity research

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. The population dynamics of organisms can then be simulated against the background of shifting environmental conditions.

“With our model, we can show how complex geological, climatic and biological processes interact and how different biodiversity patterns emerge,” Hagen 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. With further simulations, the researchers want to investigate how biodiversity arose in other species-rich regions and how it could develop further under different conditions in the future.

The re­search­ers are now re­fin­ing the model and run­ning sim­u­la­tions to un­der­stand the emer­gence of biod­iversity in other species-​rich re­gions and  how it might evolve under different conditions. 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.

Original publication:
(Researchers with iDiv affiliation bold)

Hagen, O., Skeels, A., Onstein, R., Jetz, W., Pellissier, L. (2021): Earth history events shaped the evolution of uneven biodiversity across tropical moist forests. Proc Natl Acad Sci USA October 5, 2021 118 (40) e2026347118; doi: https://doi.org/10.1073/pnas.2026347118

Hagen, O., Flück, B., Fopp, F., Cabral, J. S., Hartig, F., Pontarp, M., et al. (2021): gen3sis: A general engine for eco-​evolutionary simulations of the processes that shape Earth’s biodiversity. PLoS Biol 19(7): e3001340. doi: https://doi.org/10.1371/journal.pbio.3001340

Contact:

Dr Oskar Hagen(German, English)
Postdoc of the Junior Resarch Group Evolution und Adaptation at German Centre for Integrative Biodiversity Research (iDiv)
Halle-Jena-Leipzig

Leipzig University
Email: oskar.hagen@idiv.de

Dr Renske Onstein
Head of the junior research group Evolution and Adaptation
German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig
Phone: +49 341 9733 -129
Web: www.idiv.de/en/groups_and_people/core_groups/evolution_and_adaptation.html

Urs Moesenfechtel, M.A.
Media and Communications
German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig
Phone: +49 341 9733106
Email: urs.moesenfechtel@idiv.de
Web: www.idiv.de/media