The Kihansi spray toad is currently extinct in the wild after its habitat was impacted by a dam. Photo by: Rhett A. Butler.
So, here’s the good news: a mass extinction, the world’s sixth, is still preventable. But the bad news: if species currently threatened with extinction vanish—even over the next thousand years—homo-sapiens will be the first single species responsible for a mass extinction. Comparing today’s current extinction crisis with the big five that occurred in the past, a new study in Nature finds that while the situation is dire, the choice is ultimately up to humanity.
“If you look only at the critically endangered mammals—those where the risk of extinction is at least 50 percent within three of their generations—and assume that their time will run out, and they will be extinct in 1,000 years, that puts us clearly outside any range of normal, and tells us that we are moving into the mass extinction realm,” explains lead author Anthony D. Barnosky, UC Berkeley professor of integrative biology.
Currently, there are 3,565 species listed as Critically Endangered by the International Union for the Conservation of Nature (IUCN) Red List, however the IUCN has only evaluated around 2.7% of the world’s species.
 Native to the Indonesian island of Sulawesi, the black-crested macaque (Macaca nigra) is classified by the IUCN Red List as Critically Endangered. Photo by: Rhett A. Butler. |
Barnosky added that if species classified as Endangered and Vulnerable go extinct as well, the world could suffer a sixth mass extinction within 300 to 2,200 years. A recent analysis by the International Union for the Conservation of Nature (IUCN) found that 20% of the world’s vertebrates were currently threatened with extinction. Most of the world’s invertebrates have not even been surveyed for such threats.
According to Barnoksy, 1-2% of the world’s species have vanished ” in the groups we can look at clearly”, implying that there is still time. But extinctions are still happening faster than they did even during past mass extinctions.
“Just because the magnitude is low compared to the biggest mass extinctions we’ve seen in a half a billion years doesn’t mean to say that they aren’t significant,” coauthor Charles Marshall, UC Berkeley professor of integrative biology said. “Even though the magnitude is fairly low, present rates are higher than during most past mass extinctions.”
Looking at mammals, the study found that current extinction rates were far higher than average: at least 80 mammals have gone extinct in the past 500 years, however, researchers found that looking at the fossil record showed that an average of less than 2 mammals going extinct every million years.
“It looks like modern extinction rates resemble mass extinction rates, even after setting a high bar for defining ‘mass extinction,'” Barnosky commented.
Some groups are even more endangered than mammals. According to the IUCN, 33% of amphibians, 27% of reef-building corals, 29% of conifers, and 52% of cycads are currently threatened with extinction.
Life is currently being diminished by a multitude of human impacts including deforestation, habitat loss, pollution, over-exploitation for food and traditional medicines, invasive species, and climate change.
 The Critically Endangered Aruba island rattlesnake at the Bronx Zoo. Photo by: Rhett A. Butler. |
“The modern global mass extinction is a largely unaddressed hazard of climate change and human activities,” said H. Richard Lane, program director in the National Science Foundation’s Division of Earth Sciences, which funded the research. “Its continued progression, as this paper shows, could result in unforeseen—and irreversible—negative consequences to the environment and to humanity.”
Biodiversity, the richness of life on Earth, provides a number of services to humanity such as pollination, pest control, medicinal discoveries, food production, fisheries, carbon sequestration, freshwater, and, of course, the immeasurable value of sharing the world with a wide-variety of weird and wonderful life-forms.
“Our findings highlight how essential it is to save critically endangered, endangered and vulnerable species,” Barnosky added. “With them, Earth’s biodiversity remains in pretty good shape compared to the long-term biodiversity baseline. If most of them die, even if their disappearance is stretched out over the next 1,000 years, the sixth mass extinction will have arrived.”
CITATION: Anthony D. Barnosky, Nicholas Matzke, Susumu Tomiya,
Guinevere O. U. Wogan, Brian Swartz, Tiago B. Quental, Charles Marshall,
Jenny L. McGuire, Emily L. Lindsey, Kaitlin C. Maguire,
Ben Mersey, and Elizabeth A. Ferrer . Has the Earth’s sixth mass extinction already arrived?. Nature. 471. 51-57. 3-3-2011. doi:10.1038/nature09678.
The Sumatran orangutan (Pongo abelii) is considered Critically Endangered with approximately 7,000 left, representing an 80% decline in 75 years. Photo by: Rhett A. Butler.
A female leather-back sea turtle lays a precarious nest. The world’s largest marine turtle in the world, the leather-back is listed as Critically Endangered by the IUCN Red List. Photo by: Tiffany Roufs.
A black-and-white ruffed lemur (Varecia variegata) feeds on a tamarind in Madagascar. Their population has dropped by 80% in 27 years. This species is also listed as Critically Endangered. Photo by: Rhett A. Butler.
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