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The number of animals on the planet has fallen 52 percent in the last 40 years, according to an analysis bythe conservation organization World Wildlife Fund (WWF). The group’s Living Planet Index, which tracked the populations of more than 10,000 vertebrate species from 1970 to 2010, revealed major declines in key populations of mammals, birds, reptiles, amphibians, and fish. The situation is most dire in developing countries, the report said, where wildlife populations have fallen on average by 58 percent. Latin America saw the biggest declines, with more than 80 percent of the region’s animals lost since 1970. Globally, freshwater populations have plummeted 76 percent. This year’s numbers are worse than those calculated in the last report in 2012, which found declines of 30 percent since 1970. The organization attributed this to new statistical weighting, which it said better represents each region’s biodiversity, though other researchers have been critical of the new methodology. Habitat loss and degradation was cited as the primary cause of biodiversity loss.