At least 543 species of vertebrate land animals were lost to extinction in the last century, according to the paper, published this week in the journal the Proceedings of the National Academy of Sciences. A loss of that magnitude would normally take 10,000 years to accumulate, and it also is roughly the same number of species the study’s authors estimate will go extinct in the next two decades, reports Rachel Nuwer for the New York Times.
The loss of species and the ecosystems they comprise has real consequences for humanity, which relies on them to suck carbon dioxide from the atmosphere, clean water, pollinate vital crops, control pests and disease, as well as a host of other services, reports the Times.
When paleontologists speak of mass extinctions, they refer to relatively brief periods, geologically speaking, of Earth’s history that have erased more than three-quarters of all living species. Five mass extinctions have occurred in the past 540 million years—the most recent of which wiped out the dinosaurs. These cataclysmic die-offs were caused by violent and sudden changes such as a huge asteroid impact in the case of the dinosaurs 66 million years ago, and massive volcanic eruptions in the case of the “Great Dying” 250 million years ago. Researchers as well as Pulitzer Prize winning science journalist Elizabeth Kolbert have taken to calling the hemorrhaging of species going on now the "sixth mass extinction." As other researchers have pointed out, thankfully we have not lost 75 percent of all life on the planet, but the current rate of extinctions is well above Earth’s normal background rate.
There is a difference between this sixth mass extinction and the preceding five, according to Gerardo Ceballos, an ecologist at the National Autonomous University of Mexico and lead author of the new study. He tells Ivana Kottasova of CNN, this one “is entirely our fault.”
The other difference between past mass extinctions and this one is that we’re living through this one, and will feel its consequences if it’s allowed to continue unchecked.
“When humanity exterminates other creatures, it is sawing off the limb on which it is sitting, destroying working parts of our own life-support system,” says Paul Ehrlich, an ecologist at Stanford University and co-author of the new paper, in a statement. “The conservation of endangered species should be elevated to a global emergency for governments and institutions, equal to the climate disruption to which it is linked.”
To determine how many species are being driven towards oblivion, the authors looked at the populations of 29,400 land vertebrate species, reports Yessenia Funes for Gizmodo. They found that 515 species (1.7 percent) have fewer than 1,000 individuals remaining and are teetering on the brink of extinction, and that roughly half of those species are barely hanging on with populations smaller than 250, per Gizmodo. The researchers write that the majority of these species inhabit the world’s tropical and subtropical regions.
The species found to have less than 1,000 individuals include the Sumatran rhino, the Clarión wren, the Española giant tortoise and the harlequin frog, reports Damian Carrington of the Guardian.
When the researchers included species with populations between 1,000 and 5,000, the tally grew by 388 with 84 percent of the additions coming from the same parts of the world identified as hosting the majority of critically endangered species, according to the Times.
This geographic overlap sets up the potential for an ecologically devastating domino effect in which the loss of one species begets the loss of many others, according to the Guardian.
Ceballos tells the Times it’s like pulling bricks from a house. “If you take one brick out, nothing happens — maybe it just becomes noisier and more humid inside, but if you take too many out, eventually your house will collapse.”
For this reason, the authors argue that species with populations under 5,000 individuals should be considered critically endangered by the International Union for the Conservation of Nature, which maintains the Red List of threatened species, according to the authors’ statement.
"What we do to deal with the current extinction crisis in the next two decades will define the fate of millions of species," says Ceballos in the statement. "We are facing our final opportunity to ensure that the many services nature provides us do not get irretrievably sabotaged."
But the task before humanity isn’t merely staving off total extinction, points out Rebecca Shaw, the chief scientist at the World Wildlife Fund and who was not involved in the research, in the Times.
“The population declines of common species — top predators, large-bodied herbivores like the rhino, pollinators and others — have large effects on the way ecosystems function even when they are far from extinction,” she says. “Ceballos and his colleagues are telling us with scientific certainty that the survival of these species is linked to our own survival.”
Andy Purvis, an ecologist at the Natural History Museum who was not involved in the new paper, tells the Guardian “this research provides another line of evidence that the biodiversity crisis is accelerating...But—and this is the crucial point—it is not too late. To transition to a sustainable world, we need to tread more lightly on the planet. Until then, we are essentially robbing future generations of their inheritance.”