Earth's Biodiversity Could Take Millions of Years to Recover from Human Influence

A new study concludes that extinction rates for gastropods during the fifth mass extinction were worse than believed, and the sixth could be even bigger.
May 21, 2021, 5:05pm
Earth's Biodiversity Could Take Millions of Years to Recover from Human Influence
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In the fight against human-caused climate change, a lot of attention is understandably given to the here-and-now. But a new study has looked to the fossil record to suggest that the planet will take millions of years to recover from the current damage being inflicted by humanity.

World history has been punctuated by what scientists refer to as mass extinction events. The asteroid that triggered the fifth mass extinction, the Cretaceous-Paleogene extinction, caused at least three-quarters of the world’s species to die off was one such event, for example. Now, some 66 million years later, many scientists say we are in the middle of another mass extinction, this time driven by human activity. 

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A new study, published on Friday in the Nature journal Communications Earth & Environment, reassessed extinction rates during the fifth mass extinction for gastropods, which are freshwater snails and slugs, and predicted future rates under a business-as-usual scenario. They found that freshwater extinction rates today are three orders of magnitude higher than even the corrected extinction rate during the last mass extinction, and that they’re likely to become even worse in the future. This is an ominous sign, because the planet took millions of years to recover its biodiversity after the last extinction event.  

“66 million years ago, you had an asteroid impact that had an immediate effect on the whole world,” said Thomas Neubauer, the first author of the study and an animal ecology and systematics professor at Justus Liebig University. “Right now we have a comparable situation: it's similarly catastrophic, and the catastrophe is us, humankind.”

The researchers chose to look at freshwater gastropods in Europe because of their relative abundance in the fossil record and the high degree to which they have been preserved, Neubauer said. Previously, it was assumed that smaller life forms closer to the base of the food chain would not have been very perturbed by the asteroid impact, while the larger, apex predators were decimated. The fossil record, however, told a different story. After reconstructing the historical species richness of the aquatic slugs and snails, the researchers calculated an extinction rate more similar to the overall 75 percent rate for flora and fauna.

Aquatic gastropods play an important role in their ecosystems and as prey, and the loss of these species have cascading effects upward, Neubauer said. Additionally, global trends for freshwater life indicate that gastropods may be the rule and not the exception, according to the study. 

Next, Neubauer and his co-authors turned their eyes to the near future. Using an open source extinction simulator created by Swedish researchers, they modeled 50, 80, and 100 years of future European freshwater gastropod extinctions based on designations from the International Union for Conservation of Nature’s Red List of Threatened Species. The model took historical IUCN data as inputs and used Bayesian inference to predict how such statuses may change in the future—from endangered to extinct, for example—based on probability.

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The result was startling: the predicted rate of extinction would be much higher than that of the Cretaceous-Paleogene extinction. Of the freshwater gastropods found in Europe, “between 72 (20.8 percent) and 111 species (31.9 percent) might go extinct during the next 50 to 100 years,” according to the study.

Neubauer said that he was confident that the IUCN Red List accurately captured current species richness for the gastropods studied, since he and many other researchers contribute to data sets that are incorporated into the list. Even so, data for other groups like insects are incomplete, he added, making extrapolation difficult.

Comparing the fifth mass extinction and our current one, the sixth, provides insight into what recovery from this period may look like. It took millions of years after the immediate environmental effects of the asteroid’s impact for levels of species richness to recover—it could take just as long for global biodiversity to recover from human’s impact on it, Neubauer said.

Neubauer said he hopes the study inspires politicians to take legislative action against human-driven climate change and convinces people to take a look at their everyday decisions that affect the planet.

“Everything we do has an impact on our ecosystem,” he said. “This starts with our everyday decisions: what we are going to eat for dinner, how much meat we're going to eat, how much we're going to order online, how much are we going to fly.”