Study: Global Wildlife Population Cut in Half Since 1970

— -- The global population of wildlife has declined drastically in the past several decades, suffering a drop of 58 percent between 1970 and 2012, according to a new report from the World Wildlife Fund (WWF) and the Zoological Society of London.

The overall number of vertebrates -- a group that includes mammals, birds, reptiles, amphibians, and fish -- has fallen dramatically as a result of human activity, the conservation groups say. The groups' bi-annual Living Planet report found that animals living in freshwater systems were most at peril, seeing an 81-percent drop-off in their numbers. Wildlife populations in the world's oceans shrunk by 36 percent while on land the numbers fell by 38 percent.

If current trends continue, the groups say, more than two-thirds of all global wildlife will be in decline by 2020.

“For the first time since the demise of the dinosaurs 65 million years ago, we face a global mass extinction of wildlife," said Mike Barrett, Director of Science and Policy at WWF-UK.

The conservation groups blames human activities including deforestation, pollution, overfishing and the illegal wildlife trade, in addition to the effects of climate change, for pushing species to the edge. The biggest culprit, according to the WWF, is habitat loss and degradation caused mainly by the global food system.