The World Wildlife Fund announced in 2014 that the world has lost over 50% of its vertebrate wildlife (mammals, birds, reptiles, amphibians and fish) in the last 40 years. The cause is primarily due to an exponential growth in human consumption.
Here are two good articles on the subject:
The Guardian Earth has lost half of its wildlife in the past 40 years, says WWF
George Monbiot The Kink in the Human Brain