Are we threatening what almost destroyed the living environment 252 million years ago? The results of a study suggest that a critical loss in biodiversity formed a tipping point in the so-called Permian-Triassic mass extinction event. Accordingly, the ecosystems were initially able to remain stable despite considerable losses. However, in the second phase, species losses due to environmental changes then exceeded a critical level. As a result, the food web collapsed and the mass extinction reached its full extent, the scientists suspect.
The history of life was marked by a few drumbeats: after phases of development, there were sometimes drastic cuts, during which many species suddenly disappeared. Perhaps the most famous is the mass extinction that wiped the dinosaurs from the stage of evolutionary history around 66 million years ago. But there was something even worse before that: the mass extinction at the end of the Permian era around 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 out.
Various indications show that this collapse was due to the consequences of gigantic volcanic eruptions. They released large amounts of carbon dioxide into the atmosphere, leading to severe global warming. The parallel to today's - albeit man-made - crisis is therefore obvious: it is assumed that similar effects occurred back then as are emerging in the context of current climate change: the marine creatures of the Permian age were probably caused by the temperature increases, acidification of the water and create oxygen deficiency. It can be assumed that at some point the food chains broke down, which left the rest of the world behind.
On the trail of the primeval ecosystem collapse
But how exactly could this have happened? An international team of researchers has now investigated this question. For their study, they examined the enormously 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 perfect for our study because we need plenty of fossils to reconstruct food webs," says co-author Michael Benton of the University of Bristol. "The rock sequences there can also be dated very precisely, so that we were able to follow the extinction process closely," explains the scientist.
In this way, the researchers were able to document how biodiversity developed at that time. They also assigned the fossil creatures 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 relationships between predators and prey. This ultimately enabled scientists to develop models that simulate how ecosystems were structured before, during, and after the extinction event.
As the team reports, two phases emerged in their results: "Despite the loss of more than half of the species in the first phase of the extinction, the ecosystems remained relatively stable," reports lead author Yuangeng Huang from the Chinese University of Geosciences in Wuhan. Thus, the interaction systems between the species did not suffer significantly in this period of extinction. But this was different in the second phase: The losses reached a level that probably led to critical destabilization: "The ecosystems were brought to a tipping point from which they could no longer recover," says Huang.
“Functional redundancy” is important
As the researchers explain, it is known that an ecosystem as a whole is more resilient to environmental change when there are multiple species that perform similar functions. Because if one species fails, a similar one can fill the gap and take over the role and the ecosystem remains stable. This can be compared to an economic system where several companies provide the same products or services that others depend on. The loss of just one company can be coped with. But the fewer there are, the greater the risk that further losses will result in the entire system collapsing.
"Our results reflect that in the first phase of the extinction there was only a loss of functional redundancy, leaving a sufficient number of species to perform essential functions," says co-author Peter Roopnarine of the California Academy of Sciences in San Francisco. "But later, as environmental disturbances such as global warming or ocean acidification increased, ecosystems lacked the enhanced resilience, leading to an abrupt ecological collapse."
The scientists are once again focusing on today's crisis: For them, the results underline how important it is to maintain functional redundancy in today's ecosystems - i.e. to protect biodiversity. “We are currently losing species at a faster rate than any other extinction event in the past. It's likely that we're in the first phase of another, more severe mass extinction event," Huang said. In conclusion, he therefore emphasizes how important it is to consistently fight against all factors that contribute to the loss of biological diversity.
Source: California Academy of Sciences, professional article: Current Biology, doi: 10.1016/j.cub.2023.02.007