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“Sixth Extinction” Numbers: We multiplied by 35 the rate of species extinction

Humans are cutting branches from the “tree of life” at a record rate, according to calculations published on Monday. Gerardo Ceballos and Paul Ehrlich in the magazine PNAS. Researchers examined the conservation status of more than 34,000 extinct and endangered terrestrial vertebrates, including 5,400 genera, from the International Union for the Conservation of Nature and Birds between 1500 and 2022. 73 entire genera, 10 families, and 2 orders of vertebrates became extinct, an extinction rate 35 times higher than the average extinction rate of the previous million years.

The results also show that birds suffered the greatest loss, with 44 genera becoming extinct, followed by mammals, amphibians and reptiles. The researchers also calculate that a genus lost in the last five centuries would take 18,000 years to become extinct without human pressure, giving an idea of ​​the impact of our activities on evolution.

Looking to the future, the authors predict that the current rate of extinction is likely to accelerate significantly in the coming decades due to factors accompanying human growth and consumption, such as habitat destruction, illegal trade and climate change. If all endangered genera disappeared by 2100, the extinction rate would average 354 times the previous rate (511 times higher for mammals). They point out that this means that a genus lost in three centuries would have needed between 106,000 and 153,000 years to become extinct in the absence of humans.

Genres lost in the last five centuries would take 18,000 years to become extinct without human pressure.

“We decided to use the analogy that Darwin used about the ‘tree of life’ because it is perfectly understandable,” Ceballos explains to “And we’re talking about tree mutilation, because that’s really what happens; “We cut branches in a harmful way and lose small and big branches. The essential value of the study is that it turns a magnifying glass on the losses of evolutionary units larger and more complex than simple species, he emphasizes. “When you lose some species, you don’t lose their entire evolutionary history, but if you lose an entire genus, yes. “We’re losing a large part of the evolutionary history of the planet, and that has consequences for humans,” he says.

Tangible results

According to the authors, our activities are “totally transforming the biosphere” and destroying the “generic library” of species, which will affect ecosystem functioning and services, including primary productivity, biogeochemical cycles and interactions between species, among many others. . For this they give several examples such as disappearing Passenger pigeons in North America and argue that the loss of a widespread genus can affect the functioning of an entire ecosystem.

We are losing much of the evolutionary history of the planet, and this has consequences for humans.

Gerardo Ceballos
Main author of the article

“Anthropogenic extinctions of passenger pigeons have reduced the human diet in northeastern North America and altered ecosystem structure over large areas,” they write. “Together with other extinctions and population declines (e.g., cougars and wolves) and resulting changes in rodent communities, the region likely became ripe for the spread of many zoonotic infectious diseases, such as the tick-borne spirochete (Borrelia burgdorferi), which causes Lyme disease, a nasty and increasingly common human disease.”

Regarding the difference in extinction rates, Ceballos believes that birds and mammals have more extinct genera than amphibians and reptiles for a methodological issue, since the latter were not paid attention to until relatively recently. The bird’s high extinction rate, he notes, is partly explained by what happened with the colonization of the islands in the 17th and 18th centuries, when species like the dodo, which lived without predators, fell victim to species invasions. carried by humans. “But those distinctions are disappearing,” he warns, “and now we’re affecting basically every animal, from mice to elephants, from snails to rhinos.”

Measure evolutionary impact

For the Spanish researcher Fernando Valladares, director of the Ecology and Global Change Group at the National Museum of Natural Sciences (MNCN-CSIC), this study is the most serious quantification of the evolutionary impact of species loss and emphasizes the consideration of evolutionary aspects and not. Only ecological. “We’re so used to counting and measuring in numbers, and that’s not representative of what really matters, because there are more relevant species and others less, and more functionally redundant species, meaning we have more in terms of function.” alternatives,” he explains. “This also happens from a phylogenetic point of view; There are species that are the last remnants of some groups and others that represent more widespread groups.

According to Valladares, what these data and predictions tell us about the future is the evolutionary time we are losing, the time it will take for nature to recover some species and groups. “And we’re going to need thousands of years, which we don’t have, because evolution is never going to go that fast, and the less raw material you have, the less species and functional and phylogenetic diversity you can create, so the chances of meeting a climate change like the one we’re having now diminishes exponentially.”

Environmental erosion develops at such a fast pace that organisms do not have time to adapt.

Daniel Pincheira-Donoso
Queen’s University Belfast

“The big problem revealed by the results of this study is the speed at which this lineage will become extinct,” he warns. Daniel Pincheira-DonosoResearcher at the Microbiodiversity Laboratory, Faculty of Biological Sciences, Queen’s University Belfast (United Kingdom). Scientific Media Center. “This phenomenon is evidence that the erosion of the environment caused by the expansion of human industrial activity is proceeding at such an accelerated rate that the organisms inhabiting the earth do not have time to adapt to these changes, which leads to its collapse.” On the other hand, he notes, given that we may not yet have discovered and cataloged more than 25% of the species that exist on Earth, it is possible that the rates of extinction of species and entire genera were just the tip of the iceberg. Iceberg.

David BuckleyThe evolutionary biologist and professor of genetics at the Autonomous University of Madrid (UAM) agrees that we are only seeing a fraction of the lost biodiversity. “If you look at how many species of mammals or insects are extinct, we know that there are many more than we know, and that many of them disappear before we can describe them,” he confirms. The researcher believes that the approach of this new study is correct and consistent with the accelerated extinction that other groups are registering. “I’ve been working on amphibians, and we’ve been seeing both population declines and extinctions of some species for many years,” he notes. “And, from a more ecological point of view, we see things in the places we go and we no longer see things because the environment has changed; “Where there used to be fields, it turns out to be urbanized or cultivated.”

“Such mutilation of the tree of life and consequent loss of ecosystem services provided to humanity by biodiversity is a serious threat to the stability of civilization,” the authors of the study note. “Immediate political, economic and social efforts on an unprecedented scale are necessary if we are to avoid these extinctions and their social impacts.” “There are ethical, moral and philosophical reasons to stop species becoming extinct, but the most important one is that it’s like we’re losing bricks from a building,” Ceballos concludes. “Because at the moment the wall is still standing, but eventually it may come down and we are the victims.”

Source: El Diario





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