The Permian-Triassic extinction event is mostly known for the devastating impact it had on the ocean ecosystems, wiping out up to 96% of all marine species. However land-based animals took a pounding too, and new research shows that it took some 8 million years for the terrestrial ecosystems to fully recover.
Researchers from Brown University and the University of Utah have published a paper in the journal Proceedings of the Royal Society B in which they detail the exhaustive specimen-by-specimen analysis they conducted in an attempt to determine the extent to which land-based animals suffered as the Permian drew to a close.
Only a handful of genera survived, labelled “disaster taxa” that were able to roam freely, unhindered by the predators that had existed previously. However, as a result, chinks in the food-web allowed external forces to wreak even greater havoc than normal, creating vicious boom-and-bust cycles in the ecosystems. The lack of animals and animal diversity in the various ecosystems meant that it was harder to survive environmental and other changes, note the authors.
As a result of these boom-and-bust cycles, it took the terrestrial ecosystems some 8 million years to fully rebound from the extinction event, through incremental evolution and speciation.
“It means the (terrestrial ecosystems) were more subject to greater risk of collapse because there were fewer links” in the food web, said Jessica Whiteside, assistant professor of geological sciences at Brown and co-author on the paper.
The boom-and-bust cycles that marked land-based ecosystems’ erratic rebound were like “mini-extinction events and recoveries,” said Randall Irmis, a co-author on the paper, who is a curator of paleontology at the Natural History Museum of Utah and an assistant professor of geology and geophysics at Utah.
This hypothesis – that the ecosystems recovery post-Permian was entirely dependent upon repopulation and diversification, rather than a smoothing out of climate – mirrors conclusions that Whiteside and a colleague published in the journal Geology in 2010, in which they speculated it took up to 10 million years after the Permian-Triassic extinction event for enough species to repopulate the ocean so that the marine ecosystem could stabilise, healthy food-web and all.
“It really is the same pattern” with land-based ecosystems as marine environments, Whiteside said. The same seems to hold true for plants, she added.
This is a different answer to why it took so long for the species to recover than some studies have argued. Many have thought that continued volcanism following the end-Permian extinction was the result for extending the ecosystems recovery time, but Whiteside and Irmis stress that there is no evidence for such a theory.
The researchers studied nearly 8,600 specimens known to be from the end of the Permian to the middle Triassic, roughly 260 million to 242 million years ago, gathered from sites in the southern Ural Mountains of Russia and from the Karoo Basin in South Africa.
The specimen count and subsequent analysis showed that roughly 78 percent of land-based vertebrate genera perished in the Permian-Triassic extinction event.
“Comparison with previous food-web modeling studies suggests this low diversity and prevalence of just a few taxa meant that links in the food web were few, causing instability in the ecosystem and making it susceptible to boom-bust cycles and further extinction,” Whiteside said.
Source: Brown University
Image Source: Victor Leshyk via Brown University