NC State researchers look to history to see what survivors of major extinctions look like.
How survivors adapt in a post-apocalyptic world
October 27, 2017
The burning question I have every time I watch a movie featuring a major disaster or apocalypse, is what does the world look like with few remaining survivors?
As bad as the alien invasion sequel "Independence Day: Resurgence" was—and it was that bad—it was interesting to see how the surviving humans were able to adapt the remnants of alien technology to help humanity rebuild and gird themselves for planetary defense.
It's an interesting thought exercise: after all the zombies are defeated or when the tidal waves recede, what does a society built by the 25-or-so survivors look like? Does it eventually crash back toward a society filled with pre-disaster-like people, or does the world become populated with millions of action hero types trying to out-rescue and out-cheesy-one-liner each other?
The really cool thing about Earth being 4 billion years old is that we have plenty of history to comb through for answers to these questions, and it turns out that Earth has experienced a few apocalypses over the millennia. These so-called mass extinction events live up to their name, usually wiping out more than half the species on the planet, and they happen every 50 million to 100 million years.
Researchers from North Carolina State University looked at two of those extinction events to find out what a post-apocalyptic society looks like, biologically speaking. They found that we may always return to a normal society, but there are a few million years every time during which everyone is a Schwarzenegger.
Fossil records from more than 900 species showed that in the case of two extinction events separated by tens of millions of years, a few rugged generalist species survive, spread and adapt to the world that is now theirs. The research was published in the journal Nature Communications.
David Button, a postdoctoral researcher at NC State and the North Carolina Museum of Natural Sciences examined species from the extinction events separating the Permian and Triassic Periods 260 million years ago and the Triassic and Jurassic Periods 175 million years ago. In both cases, the few survivors eventually branched out and specialized to fit every biological niche, but there was a time after each event where those unspecialized, adaptable, can-do survivor species had the world to themselves.
Biogeographers refer to these survivalists as “weedy species”: species that have a knack for springing up anywhere they go, just like weeds. Button tracked not only to what degree those weedy species spread, but also how future species were related to those weedy ones and how long it took for the descendants of those survivors to specialize once again.
He found that after each extinction event, there was a huge spike in what biogeographers call “cosmopolitanism"—a state where the species in every comparable habitat look essentially the same. By the end of the Triassic period, right before the second extinction event, that cosmopolitanism plummets to minimal levels, showing that species return to a more ‘normal’ distribution.
Every extinction event has left survivors. Proto-mammals and birds outlasted the dinosaurs at the end of the Cretaceous period. Crocodylomorph reptiles outlived their cousins at the end of the Triassic. All of those species and the early dinosaurs were among the 25 percent of land animals that survived the Permian extinction. There are even theories that the sole survivors of the earliest extinction events were those lucky few bacteria that could survive in space, hitchhiking on rocks that a meteoric impact flung away from Earth, only to fall back later.
In each of those cases, a robust, diverse and specialized ecosystem grew. But for that to happen, we have always relied on generations of Rambos, dealing with whatever came their way.
Daniel Lane covers science, medicine, engineering and the environment in North Carolina.