WWF estimates that Earth has [ lost half its wild animals since 40 years ago ]( http://www.theguardian.com/environment/2014/sep/29/earth-lost-50-wildlife-in-40-years-wwf ) . They have been wiped out by human activity and its consequences. I think the count refers to vertebrates only.
Ссылка: https://stallman.org/archives/2014-jul-oct.html#30_September_2014_%28Earth_has_lost_half_its_wild_animals_since_40_years_ago%29