The most severe known mass extinction event eradicated over eighty percent of marine species. Yet, notwithstanding these massive losses, numerous ecosystems did not collapse, and a multitude of animals, including apex predators, managed to survive the catastrophe.
Research findings indicate that the fate of each ecosystem was partly determined by its distinct assemblage of species. This same principle might also apply to contemporary marine ecosystems, which are currently facing considerable threats from climate change. The outcomes of a new study have been published in bioRxiv.
The Permian extinction occurred approximately 252 million years ago. It appears to have been precipitated by vast volcanic eruptions in what is now Siberia, triggering rapid global warming, oxygen depletion in the oceans, and a host of other perils. Certain animal groups, such as trilobites and eurypterids (sea scorpions), were completely wiped out; others experienced enormous reductions. Following this, many new lineages emerged, including dinosaurs and ichthyosaurs. Given the sheer extent of species loss, researchers hypothesized that ecosystems became significantly simplified post-extinction.
A fully operational ecosystem comprises numerous interdependent species: plants producing sugars via solar energy, herbivores consuming the plants, predators feeding on herbivores, and potentially top predators preying on smaller carnivores. However, fauna positioned at higher “trophic levels,” like apex predators, may be more susceptible to extinction because their survival hinges on the availability of prey. Consequently, a mass extinction event akin to the Permian one would ostensibly eliminate trophic levels, leaving behind less complex ecosystems.
To ascertain if this indeed transpired, Baran Karapınar from the University of Leeds in the UK, alongside his colleagues, examined preserved remnants from seven marine ecosystems globally, dating from immediately before and shortly after the extinction. They inferred the structure of each ecosystem based on the species present. Karapınar declined an interview as the research has not yet undergone peer review.
Despite the disappearance of up to 96 percent of species, five out of the seven ecosystems maintained at least four trophic levels.
In most areas, particularly those nearer the poles, the greatest declines were observed among herbivorous animals, which were often slow-moving and benthic (seabed dwelling). In contrast, organisms capable of free swimming in the open water, such as fish, suffered lesser impacts.
After the disaster, ecosystem recovery varied depending on proximity to the equator. Tropical ecosystems were dominated by lower trophic level fauna, like herbivorous bottom-dwellers. Conversely, ecosystems situated closer to the poles acquired additional trophic levels as predatory animals, like fish, migrated away from the equator to escape the most severe heat.
“I am unaware of any other study that synthesizes this many regions,” comments Peter Roopnarine from the California Academy of Sciences in San Francisco. He concurs with the conclusion that many ecosystems retained their trophic levels despite species loss, a notion supported by smaller-scale research. Nevertheless, Roopnarine cautions against placing too much faith in the specific ecosystem models devised by the researchers. For instance, they had to group all photosynthetic organisms into a single category because the fossil record doesn’t specify which ones survived and which vanished—thus precluding them from modeling the impact of extinctions within that foundational group. “Their data aligns with the paleontological record, but the paleontological record is incomplete,” he observes.
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