National Geographic News
PHOTOGRAPH BY JOHN EASTCOTT AND YVA MOMATIUK, NATIONAL GEOGRAPHIC
The 2014 Living Planet Report gives an index that tracks the numbers of animals in selected populations of vertebrates—mammals, birds, reptiles, amphibians, and fish—across the globe.
This "Living Planet Index" declined by 52 percent between 1970 and 2010, "a much bigger decrease than has been reported previously," according to the report.
The 52 percent figure refers to a general trend of vertebrate species populations shrinking, on average, to about half the size that they were 40 years ago, according to WWF spokesperson Molly Edmonds.
The report attributes the declines primarily to habitat loss and degradation, hunting and fishing, and climate change.
Though the new index received intense global media attention, establishing a broad trend for all animals is difficult—and controversial—because of the limited data on global wildlife populations. At least one prominent ecologist raised questions Tuesday about World Wildlife Fund's methods.
A Changing Picture
Two years ago, WWF put the same decline at 28 percent for nearly the same time period: 1970 to 2008. For this year's report, the group recalculated the index.
"This new index used a different methodology, taking vertebrate diversity into account. And we have more data than before," Edmonds told National Geographic by email.
The new method attempts to solve the problem of limited data on the world's wildlife. Even the 3,038 vertebrate species included in the report are just a fraction of the estimated 62,839 species that have been described around the world. The new index assigns a statistical weight to underrepresented groups to "provide a better representation of the results we would expect if a complete dataset was available—containing all vertebrate species," according to the report.
In temperate regions, for example, the index now shows a decline in wildlife, whereas in 2012 the index showed an increase. "This is because bird and mammal species dominate this dataset and are increasing on average," the report says. The new method gives more weight to reptiles, amphibians, and fish populations, which are largely declining, resulting in an overall loss for the region.
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