Ur mass extinctions with current reference – wissenschaft.de

Are we threatened by what almost destroyed the living environment 252 million years ago? The results of a study indicate that the critical loss in biodiversity marked a turning point in the so-called Permian-Triassic mass extinction event. Accordingly, ecosystems initially managed to maintain their stability despite significant losses. However, in the second stage, species losses due to environmental changes exceeded the critical level. As a result, the food web collapsed and mass extinction reached its limit, scientists believe.

The history of life was marked by a few drumbeats: after the stages of evolution, there were sometimes severe cuts, during which many species suddenly disappeared. Perhaps the most famous of these is the mass extinction that wiped out the dinosaurs from the stage of evolutionary history about 66 million years ago. But there was something worse before that: the mass extinction at the end of the Permian period about 252 million years ago destroyed a large part of the already diverse living environment. The seas were particularly affected: up to 95 percent of all marine species died.

Various indications indicate that this collapse was due to the consequences of giant volcanic eruptions. They released large amounts of carbon dioxide into the atmosphere, which warmed the Earth. So the parallel with today’s – albeit man-made – crisis is clear: similar effects presumably occurred at that time as they appear in the context of current climate change: marine organisms in the Permian period may have been caused by higher temperatures, acidification of the water and creation of anoxia . It can be assumed that at some point the food chains collapsed, leaving the rest of the world behind.

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On the trail of primitive ecosystem collapse

But how exactly could this happen? An international team of researchers has now investigated this question. For their study, they examined the extremely rich fossil record found in southern China. At the end of the Permian period, there was a shallow sea with a very rich fauna. “The sites in China were ideal for our study because we need a lot of fossils to reconstruct food webs,” says co-author Michael Benton from the University of Bristol. “The rock sequences there can also be dated very accurately, so we can follow the extinction process more closely,” explains the scientist.

In this way, the researchers were able to document how biodiversity evolved at that time. They also assigned fossil organisms to “guilds” based on their characteristics – groups of species that use resources in a similar way. This revealed their ecological functions in the food web as well as the network of predator-prey relationships. This eventually enabled the scientists to develop models that simulate how ecosystems were structured before, during, and after an extinction event.

As the team reported, two phases emerged in their findings: “Although more than half of the species were lost in the first phase of the extinction, the ecosystems remained relatively stable,” reports lead author Yuangeng Huang of the Chinese University of Geosciences in Wuhan. Thus, the interaction systems between species did not suffer significantly in this extinction period. But this was different in the second phase: the losses had reached a level that might have led to critical destabilization: “Ecosystems have reached a tipping point from which they can no longer recover,” Huang says.

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Functional redundancy is important

As the researchers explain, an ecosystem as a whole is known to be more resilient to environmental change when there are multiple species performing similar functions. Because if one species fails, a similar species can fill the gap and take over the role and the ecosystem remains stable. This can be compared to an economic system where many firms provide the same products or services on which others depend. Only one company can handle the loss. But the fewer there are, the greater the risk of more losses in the collapse of the entire system.

“Our results reflect that in the initial stage of extinction, there was only a loss of functional redundancy, leaving enough species to perform essential functions,” says co-author Peter Roopnarine of the California Academy of Sciences in San Francisco. “But later, with the increase of environmental disturbances such as global warming or ocean acidification, ecosystems lacked the enhanced resilience, leading to sudden ecological collapse.”

The scientists are once again focusing on today’s crisis: for them, the findings underscore how important it is to maintain functional redundancy in existing ecosystems – that is, to protect biodiversity. “We are currently losing species at a faster rate than any other extinction event in the past. It is likely that we are in the first phase of another, more severe mass extinction event,” Huang said. In conclusion, he thus stresses the importance of the continued struggle against all factors that contribute to the loss of diversity. biological.

Source: California Academy of Sciences, professional article: Current Biology, doi: 10.1016/j.cub.2023.02.007

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