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November 3, 2018 02:34 pm

Have We Really Wiped Out 60 Percent of Animals?

Remember that study which reported humanity had wiped out 60 percent of animal populations since 1970? The researchers' findings "have been widely mischaracterized," reports the Atlantic's science writer -- while adding that "the actual news is still grim." The researchers had studied sample population estimates representing 4,000 of 63,000 known vertebrate species -- or 6.4 percent -- then performed a scientific extrapolation:Ultimately, they found that from 1970 to 2014, the size of vertebrate populations has declined by 60 percent on average. That is absolutely not the same as saying that humans have culled 60 percent of animals -- a distinction that the report's technical supplement explicitly states. "It is not a census of all wildlife but reports how wildlife populations have changed in size," the authors write. To understand the distinction, imagine you have three populations: 5,000 lions, 500 tigers, and 50 bears. Four decades later, you have just 4,500 lions, 100 tigers, and five bears (oh my). Those three populations have declined by 10 percent, 80 percent, and 90 percent, respectively -- which means an average decline of 60 percent. But the total number of actual animals has gone down from 5,550 to 4,605, which is a decline of just 17 percent. For similar reasons, it's also not right that we have "killed more than half the world's wildlife populations" or that we can be blamed for "wiping out 60 percent of animal species" or that "global wildlife population shrank by 60 percent between 1970 and 2014." All of these things might well be true, but they're all making claims about metrics that were not assessed in the Living Planet Index... The average 60 percent decline across populations also obscures the fates of individual species. In the hypothetical scenario above, lions are still mostly fine, the tigers are in trouble, and the bears are on the brink of extinction. And of the species covered in the actual Living Planet Index, half are increasing in number, while only half are decreasing. This means that for those that are actually in decline, the outlook is even worse than it first appears. The science writer also points out that vertebrates studied are vastly outnumbered by the millions of species of invertebrate, "which make up the majority of animal life..." "None of this is to let humanity off the hook... At least a third of amphibians face extinction, thanks to climate change, habitat loss, and an apocalyptic killer fungus. "

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