Reconsidering Extinction and Survival: Scientists Discover Potential Breakthrough in Understanding Species Aging

A University of Kansas study suggests that the neutral theory of biodiversity, which views species extinction as mostly random, delivers a more precise explanation than the prevailing Red Queen theory. This revelation carries significant consequences for biodiversity preservation, underscoring the unpredictably of species extinction and potential for gaining insight into community-level dynamics. Credit: SciTechDaily.com

The University of Kansas spearheaded a recent study that may elucidate the enigma of the “aging process” in species — or more accurately, the shifting risk of extinction that a species are exposed to from its appearance.

Traditionally, evolutionary biologists have held the belief that older species have no distinct advantage over younger species when it comes to evading extinction — a viewpoint known as the “Red Queen theory” within the research community.

James Saulsbury, the lead researcher and postdoctoral fellow in the Department of Ecology & Evolutionary Biology at KU, noted that the Red Queen theory proposes that species must consistently adapt to maintain their current position, drawing comparison to the character in Lewis Carroll’s ‘Through the Looking-Glass’. This concept was co-opted into an ecological theory in the 1970s aimed at clarifying why the risk of extinction didn’t seem to alter during a species’ lifespan.

This theory, however, has not weathered the passage of time very well.

According to Saulsbury, initial investigations into this topic found all species, regardless of age, seemed to face extinction at the same rate, which is in line with the Red Queen model of constant competition from other concurrently adapting species. This was due to the lack of comprehensive evidence at that point in time, Saulsbury explained.

As more data was accumulated and subjected to deeper analysis, an increasing number of opposing views to Red Queen theory began to surface.

Saulsbury's new model from the University of Kansas supports the recent findings of age-dependent extinction and underlines the significance of zero-sum competition in explaining extinction, providing a nod to the older Red Queen theory. Credit: Saulsbury et al.

Researchers continually found instances where younger species appeared to be more prone to extinction,” Saulsbury says. “Hence, we found ourselves with a theory vacuum – multiple inconsistent observations without a unified explanation.”

Now, Saulsbury's recent research published in the Proceedings of the National Academy of Sciences may hold the solution to this puzzle. Saulsbury and his team demonstrated that the neutral theory of biodiversity could accurately forecast the connection between a species’ age and its risk of extinction.

The neutral theory is a basic model featuring ecologically similar species vying for limited resources, where each species' outcome is more or less arbitrary.

This theory posits that "Species either perish or flourish from small initial population size to become less susceptible to extinction, yet they continue to face potential displacement by competitors," according to a simplified summary of the PNAS paper. By applying this theory to make predictions for the fossil record, Saulsbury and colleagues found that neutral theory quite accurately predicts fossil zooplankton survivorship and accounts for empirical deviations from Red Queen theory predictions more generally.

Saulsbury's co-authors included C. Tomomi Parins-Fukuchi from the University of Toronto, Connor Wilson from the University of Oxford and the University of Arizona, and Trond Reitan and Lee Hsiang Liow from the University of Oslo.

While the neutral theory may appear to undermine the Red Queen theory, Saulsbury points out that the latter still holds importance. Most significantly, it posits the continually relevant idea that species are locked in a zero-sum competition for finite resources, persistently striving for a greater share of nature's bounty.

He added, “Red Queen theory has been an influential and crucial concept in the evolutionary biological community, but the data from the fossil record no longer appears to support this theory," However, Saulsbury doesn't think the new research completely dismisses Red Queen theory because both theories bear a striking resemblance. They both depict extinction as an outcome of interspecies competition for resources and continual turnover resulting from biological interactions in communities.

In conclusion, these findings are instrumental in not only understanding the factors that shape the natural world but also may have relevance to conservation efforts, particularly as species across the globe face rising threats from climate change and habitat destruction.

“What makes a species vulnerable to extinction?” Saulsbury asked. “People are interested in learning from the fossil record whether it can tell us anything to help conserve species. The pessimistic side of our study is that there are ecological situations where there isn’t a whole lot of predictability in the fates of species; there’s some limit to how much we can predict extinction. To some extent, extinction will be decided by seemingly random forces — accidents of history. There’s some support for this in paleobiological studies.”

He said there has been effort to understand predictors of extinction in the fossil record, but not many generalities have emerged so far.

“There’s no trait that makes you immortal or not susceptible to extinction,” Saulsbury said. “But the optimistic side of our study is that entire communities can have patterns of extinction that are quite predictable and understandable. We can get a pretty good grasp on features of the biota, like how the extinction risk of species changes as they age. Even if the fate of a single species can be hard to predict, the fate of a whole community can be quite understandable.”

Saulsbury added a caveat: It remains to be seen how broadly the neutral explanation for extinction succeeds across different parts of the tree of life.

“Our study is also working on the geological timescale in millions of years,” he said. “Things may look very different on the timescale of our own lifetimes.”