Friday, 19 March 2021

Evolution News - Recovering From Mass Extinction Events

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After The Great Dying, the ecosystem changed drastically, and included many Lystrosaurus.
© Xiaochong Guo
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The plant-eating pareiasaurs were preyed upon by sabre-toothed gorgonopsians. Both groups went extinct during The Great Dying.
© Xiaochong Guo
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By the end of the Permian, pareiasaurs had become large and armored for self-protection. This complex ecosystem collapsed during The Great Dying.
© Xiaochong Guo
New study investigates how life on land recovered after “The Great Dying” | California Academy of Sciences

Life on Earth is incredibly robust and has come close to extinction altogether a few times but has always managed to bounce back and diversify again from a few founder species. In fact, of course, it once did that from a few founder simple cells, gradually diversifying and becoming increasingly fitted for the various environments found on and in Earth.

This recent study, published open access a few days ago in Proceedings of the Royal Society B, shows how it struggled to do so after the "Great Dying" event of 252 million years ago during the end of the Permian period, when 19 out of every twenty species went extinct. Some ecosystems in which key members have gone extinct can sometimes take millions of years to recover. This should be a salutary warning to us as humanity generates another great extinction event in what scientists now call the Anthropocene.

The study was carried out by an international team of researchers from the China University of Geosciences, the California Academy of Sciences, the University of Bristol, Missouri University of Science and Technology, and the Chinese Academy of Sciences. The news release from the California Academy of Science explains:
To better characterize “The Great Dying,” the team sought to understand why communities didn’t recover as quickly as other mass extinctions. The main reason was that the end-Permian crisis was much more severe than any other mass extinction, wiping out 19 out of every 20 species. With survival of only 5% of species, ecosystems had been destroyed, and this meant that ecological communities had to reassemble from scratch.

By studying the fossils and evidence from their teeth, stomach contents, and excrement, I was able to identify who ate whom. It’s important to build an accurate food web if we want to understand these ancient ecosystems.

Yuangeng Huang, Lead author China University of Geosciences,
Wuhan, China
To investigate, lead author and Academy researcher Yuangeng Huang, now at the China University of Geosciences, Wuhan, reconstructed food webs for a series of 14 life assemblages spanning the Permian and Triassic periods. These assemblages, sampled from north China, offered a snapshot of how a single region on Earth responded to the crises. “By studying the fossils and evidence from their teeth, stomach contents, and excrement, I was able to identify who ate whom,” says Huang. “It’s important to build an accurate food web if we want to understand these ancient ecosystems.”

Yuangeng Huang spent a year in my lab. He applied ecological modelling methods that allow us to look at ancient food webs and determine how stable or unstable they are. Essentially, the model disrupts the food web, knocking out species and testing for overall stability.

Peter Roopnarine, Co-author
Curator of Geology
California Academy of Science
The food webs are made up of plants, molluscs, and insects living in ponds and rivers, as well as the fishes, amphibians, and reptiles that eat them. The reptiles range in size from that of modern lizards to half-ton herbivores with tiny heads, massive barrel-like bodies, and a protective covering of thick bony scales. Sabre-toothed gorgonopsians also roamed, some as large and powerful as lions and with long canine teeth for piercing thick skins. When these animals died out during the end-Permian mass extinction, nothing took their place, leaving unbalanced ecosystems for ten million years. Then, the first dinosaurs and mammals began to evolve in the Triassic. The first dinosaurs were small—bipedal insect-eaters about one meter long—but they soon became larger and diversified as flesh- and plant-eaters.

We found that the end-Permian event was exceptional in two ways. First, the collapse in diversity was much more severe, whereas in the other two mass extinctions there had been low-stability ecosystems before the final collapse. And second, it took a very long time for ecosystems to recover, maybe 10 million years or more, whereas recovery was rapid after the other two crises.

Professor Mike Benton, Co-author
University of Bristol, UK
“Yuangeng Huang spent a year in my lab,” says Peter Roopnarine, Academy Curator of Geology. “He applied ecological modelling methods that allow us to look at ancient food webs and determine how stable or unstable they are. Essentially, the model disrupts the food web, knocking out species and testing for overall stability.”

“We found that the end-Permian event was exceptional in two ways,” says Professor Mike Benton from the University of Bristol. “First, the collapse in diversity was much more severe, whereas in the other two mass extinctions there had been low-stability ecosystems before the final collapse. And second, it took a very long time for ecosystems to recover, maybe 10 million years or more, whereas recovery was rapid after the other two crises.”

This is an amazing new result. Until now, we could describe the food webs, but we couldn’t test their stability. The combination of great new data from long rock sections in north China with cutting-edge computational methods allows us to get inside these ancient examples in the same way we can study food webs in the modern world.

Professor Zhong-Qiang Chen, Co-author
China University of Geosciences
Wuhan, China.
Ultimately, characterizing communities—especially those that recovered successfully—provides valuable insights into how modern species might fare as humans push the planet to the brink.

“This is an amazing new result,” says Professor Zhong-Qiang Chen of the China University of Geosciences, Wuhan. “Until now, we could describe the food webs, but we couldn’t test their stability. The combination of great new data from long rock sections in north China with cutting-edge computational methods allows us to get inside these ancient examples in the same way we can study food webs in the modern world.”
The teams findings can be read in the online journal, Proceedings of the Royal Society B:

Abstract


The Earth has been beset by many crises during its history, and yet comparing the ecological impacts of these mass extinctions has been difficult. Key questions concern the kinds of species that go extinct and survive, how communities rebuild in the post-extinction recovery phase, and especially how the scaling of events affects these processes. Here, we explore ecological impacts of terrestrial and freshwater ecosystems in three mass extinctions through the mid-Phanerozoic, a span of 121 million years (295–174 Ma). This critical duration encompasses the largest mass extinction of all time, the Permian–Triassic (P–Tr) and is flanked by two smaller crises, the Guadalupian–Lopingian (G–L) and Triassic–Jurassic (T–J) mass extinctions. Palaeocommunity dynamics modelling of 14 terrestrial and freshwater communities through a long sedimentary succession from the lower Permian to the lower Jurassic in northern Xinjiang, northwest China, shows that the P–Tr mass extinction differed from the other two in two ways: (i) ecological recovery from this extinction was prolonged and the three post-extinction communities in the Early Triassic showed low stability and highly variable and unpredictable responses to perturbation primarily following the huge losses of species, guilds and trophic space; and (ii) the G–L and T–J extinctions were each preceded by low-stability communities, but post-extinction recovery was rapid. Our results confirm the uniqueness of the P–Tr mass extinction and shed light on the trophic structure and ecological dynamics of terrestrial and freshwater ecosystems across the three mid-Phanerozoic extinctions, and how complex communities respond to environmental stress and how communities recovered after the crisis. Comparisons with the coeval communities from the Karoo Basin, South Africa show that geographically and compositionally different communities of terrestrial ecosystems were affected in much the same way by the P–Tr extinction.

All life on Earth, including human life, depends for its existence on functioning ecosystems so the extinction of a key component can result in a cascade of extinctions of several other component species of the ecosystem, and these vital ecosystems may not be able to recover quickly in response to whatever problems we solve, whether it is climate change, pollution or habitat destruction.

I have written before about the importance of biodiversity from the mere self-interest of humans for the resource of potentially useful chemicals that may yet be discovered, such as antibiotics, fungicides, etc. We now know from research such as this why conserving species is important for our own survival. We simply do not have enough time to wait for the ten million years or more it might take vital ecosystems to recover from the mass extinction we are currently causing.








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