- John Alroy, a professor of biology at Australia’s Macquarie University, says “a runaway train of extinction is now likely to produce what would be seen as a global mass extinction.”
- A large majority of the 200 extinct frog species were probably lost in the past few decades, just as extinctions and severe population crashes began accelerating in the 1970s and 1980s.
- The current extinction rate for frogs is four orders of magnitude higher than the long-term background average, Alroy found.
When John Alroy, a professor of biology at Australia’s Macquarie University, was asked by a reporter how many of the species populating Earth had already gone extinct, he realized he had no simple answer.
So he checked the scientific literature on the subject, and found that lacking, too.
It’s difficult to determine how many species have gone extinct in the past because of how hard it is to prove that an animal that hasn’t been observed recently is actually gone forever, Alroy writes in a study published this week in the Proceedings of the National Academy of Sciences.
It may be difficult to estimate how many species have truly disappeared from Earth forever, but that doesn’t mean it’s altogether impossible.
Alroy consulted lists of specimens in museum collections and published field surveys to compile data that he then analyzed using a highly conservative approach known as the Bayesian statistical method to infer the number of extinct amphibian and reptile species across the world.
The results are alarming. “It suggests that about 200 frog extinctions have occurred and hundreds more will be lost over the next century, so we are on pace to create a mass extinction,” Alroy wrote in the report, noting that the current extinction rate is four orders of magnitude higher than the long-term background average.
A large majority of those 200 frog species probably went extinct in the past few decades, just as extinctions and severe population crashes began accelerating in the 1970s and 1980s, Alroy told Mongabay in an email.
“However, there may have been quite a few species that went extinct before that point and never were described scientifically,” he added. “This is one reason of many that I think the estimate I’ve given is very conservative. The real toll could be two or three times higher.”
If so, Alroy’s findings are troubling indeed, given that frogs are a good indicator of ecosystem health — so much so that they’re often described as a proverbial “canary in a coal mine.”
Frogs are just as vulnerable or more vulnerable to threats like climate change, habitat destruction, pollution, invasive species and introduced pathogens as any other species. “In other words, the important thing about frogs, other than that they are interesting and beautiful and ancient, is that they are a good indicator of what’s probably going on with many other groups that aren’t as well documented,” Alroy said.
Based on the average extinction rate from 1971–2000, Alroy concluded that nearly seven percent of frog species may be lost within the next century (currently we’ve lost a little over three percent). He cautions in the report that while that rate may seem slow on a human time scale, it is a conservative minimum estimate — and human impacts are intensifying pressure on frog populations the world over.
“Thus, the data suggest that a runaway train of extinction is now likely to produce what would be seen as a global mass extinction on the ultimately more important landscape of geological time,” Alroy writes.
These findings would seem to be consistent with a variety of previous research that has concluded human activity is causing species to die off at a rate at least 100 times faster than historical levels and that the Earth has entered a sixth mass extinction period.
Calder found frog extinctions were particularly high in Central America, which was not surprising given the epidemic of a deadly pathogenic fungus called Batrachochytrium dendrobatidis that has been tied to major population declines. Frog populations in Australia have also been hit hard by the lethal fungus.
The geographic pattern of frog extinctions did hold some surprises for Alroy, however. Extinctions occurred in Brazil, Madagascar and New Guinea, places where there have not been well-documented population losses, suggesting there might be mass extinctions happening in the tropics that are going largely unnoticed.
The good news in Alroy’s report, if there is any, is that now that we know more clearly the extent of the problem, we can begin to discuss how to address it. Alroy writes, “Mitigating this crisis will require strong ongoing support of monitoring by field ecologists and museum scientists.”
- Alroy, J. (2015). Current extinction rates of reptiles and amphibians. Proceedings of the National Academy of Sciences: 10.1073/pnas.1508681112.