Living Planet Index

Wildlife populations around the world continue dropping precipitously, according to an important but limited and often misinterpreted assessment that's issued every two years.

Wild populations of monitored animal species have plummeted nearly 70 percent in the last 50 years, according to a landmark assessment released on Oct. 13 that highlights "devastating" losses to nature due to human activity.

The Living Planet Index, which measures trends in thousands of vertebrate species populations, shows a decline of 52% between 1970 and 2010, according to the latest edition of WWF's Living Planet Report.

In other words, the number of mammals, birds, reptiles, amphibians and fish across the globe is, on average, about half the size it was 40 years ago.