Paleontologists go back to the future, reconstruct fossilized functional diversity to inform conservation goals

Key points

• Scientists have demonstrated for the first time that functional diversity can be accurately inferred from the marine fossil record.
• Functional diversity, which measures the processes that take place within an ecosystem, is often more informative than biodiversity (the number of species in an ecosystem) for conservationists trying to restore and protect environments.
• This is a boon for the nascent field of conservation paleobiology, in which scientists compare healthy fossilized ecosystems to those from modern times that have been denuded by humans, thereby learning which functions or species are now missing and need to be restored.

Carrie Tyler is a paleontologist who uses the fossil record to reconstruct ancient food webs. This is a challenging undertaking, given that the fossil record is full of holes that encompass vast stretches of time and many types of organisms that have disappeared without a trace. Thus, every food web she’s able to resurrect from the past is bound to have missing parts, which may lead to biased conclusions.

Tyler is well aware of this problem, and over the last ten years, she’s worked with Michal Kowalewski, the Florida Museum of Natural History’s Thompson chair of invertebrate paleontology, to construct and analyze a massive dataset of marine fossils to determine just how big the problem is. Tyler and Kowalewski recently published their results in the journal Proceedings of the National Academy of Sciences in which they’re relieved to say that the fossil record, though patchy, is capable of preserving information about the functional diversity of past ecosystems.

“Functional diversity is a really important aspect of food webs,” Tyler said. “When I construct a fossil food web, I group things together based on the types of functions they perform, and then I add the ways in which they interact on top. But if I want to do that, I have to know that the data I’m working with are reliable.”

Functional diversity, which tracks whether biological processes are running smoothly, is also a critical part of conservation. With the results of this study, conservationists can now compare healthy ecosystems from the recent past to their modern counterparts that have been altered by humans. They can then use this information to set goals that will restore and protect these environments in the future.

With a clever and careful reading of the fossil record, paleontologists learn about what didn’t get preserved

Paleontology has come a long way since its sporadic and beleaguered beginnings. Leonardo da Vinci countered the prevailing idea of his time that fossils were a sort of mineral secretion of the earth by pointing out that fossilized shells had evident growth rings and bore holes, a sure sign that they’d once been part of a living organism. In 1667, Nicolas Steno had the rare and good fortune of being gifted the severed head of a great white shark by the Grand Duke of Tuscany and noted the teeth looked suspiciously similar to what were then referred to as “tongue stones,” which, according to popular lore, were petrified dragon tongues that fell from the sky. After many similar observations made throughout the 16th, 17th and 18th centuries, Georges Cuvier helped kickstart paleontology as a discipline by demonstrating that some fossils came from organisms that apparently could no longer be found anywhere on Earth, dispelling the common wisdom that species could not go extinct.

Not long after, the effects of the Industrial Revolution made it clear that species are abundantly capable of extinction. More than 240 mammal, 500 plant and 1,300 bird species have gone extinct since the last ice age 12,000 years ago. Thousands more plants and animals have disappeared from the wild and remain on life’s current roster only because a few dedicated people have kept them going in cultivation or captivity. And there are currently hundreds of thousands of endangered species that exist by only a thin margin, constantly in danger of dying out.

This period of time — and smaller subsets of it — is often unofficially referred to as the Anthropocene, a term derived from ancient Greek meaning “the age of humans.”

As the modern extinction crisis progressed, paleontologists began wondering whether their proficiency at using old remains to interpret the past could be used to help protect the species that were still around.

It just so happened that there was a pressing conservation problem that only paleontologists could resolve. As noted by the conservationist Aldo Leopold in a co-authored report for the U.S. National Park Service, “The first step in park management is historical research, to ascertain as accurately as possible what plants and animals and biotic associations existed originally in each locality.”

This is easier said than done, given that humans have only made a concerted effort to document Earth’s biodiversity over the past few centuries, but we’ve been altering Earth’s environments for millennia. In many places, looking at fossils is the only way to know what lived there before humans came along.

This need spawned the conservation paleobiology movement at the turn of the 21st century, in which the biodiversity of ancient ecosystems is used to assess the health of those same ecosystems in modern times.

Conservation paleobiology is not a field of science that can be used right out of the box. It requires a substantial amount of preliminary calibration to ensure the accuracy of its results, and it doesn’t come with instructions. This work has kept its proponents busy for the last two decades.

The primary difficulty confronting them is the incompleteness of the fossil record. Organisms made only of soft bits are unlikely to be preserved, and even animals with hard skeletons or shells are only fossilized when conditions are just right. There’s a lot that gets left out.

“The mismatch between life and death is difficult to interpret,” Kowalewski said. “It can be either because the fossil record is incomplete and just doesn’t give you adequate results, but it also could be because the ecosystem has changed very recently due to human activities.”

But paleontologists are clever. They’ve figured out they can learn about the things that didn’t make it into the fossil record by studying those that did, like sorting out the meaning of a choppy sentence by using context clues.

In the realm of marine science, Tyler, Kowalewski and their colleagues have shown that the diversity of mollusks, which have high rates of fossilization, are a reliable proxy for the general diversity of the ecosystems they were a part of. When mollusks are thriving, it’s a safe bet that most everything else in their environment is also doing well. This strategy has led to the discovery that native biodiversity in the Mediterranean has effectively collapsed and that marine communities in the Adriatic Sea are on the verge of doing so as well.

Recent studies increasingly suggest that when marine organisms other than mollusks do get preserved, it’s largely in proportion to their diversity. As an example, Tyler and Kowalewski found 574 individual worms in the recent fossil record off the coast of North Carolina. When they collected living organisms in the same spot, they found 1,640 worms. This was a far lower rate of preservation than mollusks, which numbered 53,151 fossil specimens but only 3,076 living ones. But when aggregated at the species level, the numbers weren’t nearly as far off: two fossil worm species compared to three living ones.

Their most recent contribution, described in the present study, gives the green light for even more complex and much-needed environmental assessment.

Functional redundancy helps preserve functional diversity

There are many ways of looking at an ecosystem. The simplest is to just count up all the species it contains to measure the biodiversity that exists within it. In general, the more species that exist in an area, the healthier their ecosystem is. This is similar to saying that someone who exercises regularly and maintains a good diet is more likely to be healthy than someone who is inactive and eats poorly. But this doesn’t actually tell you much about what’s going on inside their body. To know that, you have to look at how their organs and cells and other organic miscellany are functioning.

The same is true of ecosystems, which are in essence complex, invisible webs of interconnected and symbiotic interactions. Figuring out how they work requires knowing about more than just the web’s thread count.

So, back in the 20^th century, scientists developed the concept of functional diversity. Usually, biodiversity and functional diversity are in agreement, in the same way that regular exercise and good eating habits usually confer health. But this obviously isn’t always true of our bodies, which are subject to injury and disease, and it’s not always true of ecosystems either.

“You can imagine an ecosystem in which you have 10,000 species of mice that all do the same thing. Their functional diversity is very low, even though their biodiversity is high. Conversely, you can have an ecosystem with 20 species, but each of them is doing something completely different, and therefore their functional diversity is high,” Kowalewski said.

The ability to infer functional diversity from fossils is the kind of holy grail that paleontologists have long hoped might be possible to obtain but have never quite known for sure. To that end, Tyler and Kowalewski shouldered the herculean task of reconstructing the functional diversity of a living ecosystem and that of the fossilized ecosystem just beneath in an area they knew had remained relatively undisturbed by humans.

Between June 2011 and April 2013, they collected material at 52 locations in Onslow Bay, North Carolina. By the time they finished, they’d bagged more than 60,000 specimens, most of them skeletons. This was actually the same site — and the same specimens — they’d used to show that all marine organisms, hard and soft, are preserved in proportion to their diversity. When scientists undertake a years-long effort to collect a sizable portion of an ecosystem, there’s a strong incentive to get as much revelatory mileage out of it as possible.

Next came the countless hours squinting into a microscope to identify them all, a task that was greatly expedited by the skilled observation of museum volunteers, who did a first pass and grouped things together by similarity before Tyler went in and made the final determination.

“Every invertebrate that we found was identified and counted,” Tyler said.

Then they calculated the functional diversity for the living and fossil ecosystems and compared the two. The number of individual specimens of a particular species between the two was predictably skewed, but their overall functional diversity aligned surprisingly well.

Their success was due largely to something called functional redundancy, which Tyler and Kowalewski knew going in would work in their favor.

“In retrospect, we shouldn’t be really surprised at the outcome,” Kowalewski said.

Redundancy is exactly what it sounds like. In any given environment, there are multiple — often distantly related — species that perform the same function. Similar to the way in which a gas expands to fill a container, life diversifies until it fills every possible niche, with multiple organisms all vying for a limited space. This competition creates redundancy.

Marine worms and sea biscuits, for example, are two very different types of organisms, but they both infuse oxygen into ocean sediment as they burrow through it, which in turn speeds up bacterial growth, which enhances nutrient cycling. This biological surplus acts as a failsafe. A marine benthic ecosystem doesn’t collapse if it loses a large number of worms because it’s still got sea biscuits to keep the nutrient cycle going. It also ensures that burrowers, as a functional class, are represented in the fossil record.

“Many measures of functional diversity are based on presence and absence, so they are less sensitive to change in relation to abundance, and many of them are invariant to how many species perform a function. So as long as you have some type of redundancy built into the system, there will be at least some species that preserve the signal,” Kowalewski said.

This is good news for conservationists, who can now feel a little more confident that any discrepancy in functional diversity between the present and recent past is not the fault of a patchy fossil record but is instead indicative of real changes in an ecosystem. Therefore, if a function is missing, conservationists should probably focus on putting it back.

But the results come with a big caveat. Because this is the first study to demonstrate the fidelity of functional diversity in what remains of an ancient ecosystem, it is also, by default, the only study that demonstrates this, and nothing makes scientists more uneasy than a small sample size. Additional studies are needed to corroborate the findings and test them in different environments.

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