The analysis, published September 2 in Science, produced what Alroy considers to be the most accurate reflection of extinction dynamics to date. And while his data supported the notion that each group’s diversity eventually hits a limit, he didn’t find Sepkoski’s correlation between pre-mass-extinction diversity rates and post-extinction success. Each mass extinction event seemed to change the rules. Past didn’t indicate future.
In an accompanying commentary, paleontologist Charles Marshall of the University of California, Berkeley noted that Alroy’s statistical methods still need review by the paleobiology community. The Paleobiological Database, for all its thoroughness, might also be incomplete in as-yet-unappreciated ways. “There will be no immediate consensus on the details of the pattern of diversity,” he wrote. But “the pieces are falling into place.”
Enough pieces have come together for Alroy to speculate on his findings’ implication for the future, given that Earth is now experiencing another mass extinction. Starting with extinctions of large land animals more than 50,000 years ago that continued as modern humans proliferated around the globe, and picking up pace in the Agricultural and Industrial ages, current extinction rates are far beyond levels capable of unraveling entire food webs in coming centuries. Ecologists estimate that between 50 and 90 percent of all species are doomed without profound changes in human resource use.
In the past, many evolutionary biologists thought life would eventually recover its present composition, said Alroy. In 100 million years or so, the same general creatures would again roam the Earth. “But that isn’t in the data,” he said.
Instead Alroy’s analysis suggests that the future is inherently unpredictable, that what comes next can’t be extrapolated from what is measured now, no more than a mid-Cretaceous observer could have guessed that a few tiny rodents would someday occupy every ecological niche then ruled by reptiles.
“The current mass extinction is not going to simply put things out of whack for a while, and then things will go back to where we started, or would have gone anyway,” said Alroy. Mass extinction “changes the rules of evolution.”
Images: 1) A fossil skull of Dunkleosteus, an apex predator fish that lived between 380 million and 360 million years ago, and had what is believed to be history’s most powerful bite./Michael LaBarbera, courtesy of The Field Museum. 2) Graph of species diversity among marine animals of Cambrian, Paleozoic and Modern origin./Science.
See Also:
* Ecosystem Engineering Could Turn Sprawl Into Sanctuary
* 9 Environmental Boundaries We Don’t Want to Cross
* Death Star Off the Hook for Mass Extinctions
* A New Explanation for Ancient Mass Extinction
* Latest Extinction is the Greatest
* Megafauna Extinctions Not Entirely Humans’ Fault
Citations: “The Shifting Balance of Diversity Among Major Marine Animal Groups.” By J. Alroy. Science, Vol. 329 No. 5996, September 3, 2010.
“Marine Biodiversity Dynamics over Deep Time.” By Charles R. Marshall. Science, Vol. 329 No. 5996, September 3, 2010.
Brandon Keim’s Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.
http://www.wired.com/wiredscience/2010/09/mass-extinction-dynamics/