Friday, August 29, 2014

If Half of All Species Go Extinct, Will One of Them Be Us?

biodiversity jenga hero 

How many animal species do you think go extinct every year? Last week I conducted a highly unscientific polling of around 20 of my Facebook and Google Chat contacts, asking that same question. I’m not trying to brag, but I have some really smart friends, many of them with degrees in biology. Typical answers ranged from about 17 to a seemingly ludicrous 400. They were all wrong though—off by orders of magnitude*. In July, a summary article of nearly 80 papers, published in Science, stated that, “Of a conservatively estimated 5 million to 9 million animal species on the planet, we are likely losing ~11,000 to 58,000 species annually.”

If that finding is true, then every year, between .12% and 1.16% of all the animals on Earth vanish. Rodolfo Dirzo, the lead researcher on the Science study from Stanford University, points out that we’ve already lost 40% of the Earth’s invertebrate species in the last 40 to 50 years. Almost half the animals without skeletons have gone extinct within half a human lifetime. The wide range of these estimates reflects our own uncertainty on this subject, but even our low-end assessments are alarming.

Bugs and worms are gross, though; who cares if there are fewer spiders in my house now than in the arachnid-infested ‘60s? Unfortunately the future looks just as bleak for mammals. Dirzo says that if current trends hold, “in 200 years, 50% of the [mammal] species are going to be driven to the very edge of extinction.”

Naturally, all animals go extinct at some point, and it would be reassuring if the rates of extinction had always been this high. By examining the fossil record we can determine just how frequently animals have died out in the past—the “background extinction rate.” The news is bleak: The current rate of animal extinction is around 1,000 times higher than the background rate. That means we are living in the midst of the planet’s 6th mass extinction event. Like the meteoric collapse of the dinosaurs, we are experiencing massive loss of diversity and quantity of life on earth. Some researchers think that as soon as 2050, we may hit a tipping point where various kinds of environmental stress combine to jack the extinction rate jump still higher. So spectacular is this ongoing animal apocalypse that we’ve tentatively declared a new geological epoch: the Anthropocene, a world defined by humans.. 

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