Wildlife populations in the world’s tropical regions have fallen by more than 60 percent during the last four decades, according to the latest version of the Living Planet Index. The Index — which tracks populations of 2,688 vertebrate species in tropical and temperate regions worldwide — found that species abundance in the tropics declined by about 44 percent on land, 62 percent in the oceans, and 70 percent in freshwater ecosystems from 1970 to 2008. Cumulatively, species abundance declined by about 1.25 percent annually every year compared with a 1970 baseline, according to the report, which is published by the World Wide Fund for Nature (WWF) and the Zoological Society of London. Wildlife populations declined by 38 percent in Africa during that period; about 50 percent in Central and South America; and 64 percent in Indo-Pacific regions. Overall, the global index dropped almost 30 percent during the same period. These steep population declines are the result of many factors related to human activities, including deforestation, habitat loss, pollution, overfishing, and climate change.