Global Extinction Rates Could Be Way Higher Than Previously Thought

Rainforests, some of the most biodiverse regions on the planet, are being destroyed at an alarming rate. Rich Carey/Shutterstock.
Josh Davis 12 Aug 2015, 21:58

As we enter the Anthropocene, we are standing on the edge of the Earth’s sixth great extinction. Studies earlier this year revealed that we are currently experiencing extinction rates 100 times higher than what would have been expected if we didn’t exist. And yet since the 1980s, according to the International Union for the Conservation of Nature (IUCN) Red List, only 799 (a mere 0.04%) of the planet’s 1.9 million known species have so far been wiped out.

This low number, according to authors of a new study looking at global extinction rates, is often used by skeptics to question whether we are entering a global extinction event at all. But there is a bias from the IUCN. They generally tend to focus on the groups that are well documented – in other words birds and mammals – neglecting the invertebrates that account for 99% of animals that live on this planet. When these are taken into account, the researchers found that the real number of species to have gone extinct since the 1980s is somewhere in the region of a staggering 130,000. The findings have been published in Proceedings of the National Academy of Sciences

“We showed, based on extrapolation from a random sample of land snail species from all over the world, and via two independent approaches, that we may already have lost 7 percent – 130,000 extinctions – of all the animal species on Earth,” explained Robert Cowie, research professor at the Pacific Biosciences Research Center and coauthor of two studies looking into invertebrate biodiversity and extinction.

The second study, published in Conservation Biology, looked specifically at the extinctions occurring in Hawaii. While it’s well known that the species of birds in Hawaii have taken a massive hit, as is often the case with island communities as they are less resilient to change, there had been no real look at the catastrophic loss to the rest of the biodiversity. The invertebrate communities on the island are known to be spectacularly diverse and endemic, so Cowie and his team focused on these.

Specifically, they looked at a massively diverse group of land snails, from the family Amastridae. To date there have been 325 species recorded in Hawaii since the 1600s, and yet the team were only able to find evidence from modern surveys and records that 15 were still living on the islands. They reckon that the extinction rate might be as high as 14% of the fauna per decade, with this figure increasing over time. These dramatic findings, from both studies, far outstrip the numbers reported by the IUCN Red List, often the go-to publication for conservation biologists.

Considering that it’s thought around 75% of our agricultural plants are pollinated by insects, it’s worrying that they seem to be so neglected. These studies therefore highlight a very real need to include invertebrates in all future extinction rate estimates. 

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