Daniel Cressey in Nature:
Earth’s wild vertebrate populations have dropped to one-half the size they were in the 1970s, according to an analysis of more than 3,000 species. Researchers from the WWF wildlife NGO, headquartered in Woking, UK, and the Zoological Society of London (ZSL) aggregated data on 10,380 populations from 3,038 species into an index of the health of the five main groups of vertebrates — mammals, birds, reptiles, fishes and amphibians. Set at 1 in 1970, this index has decreased to 0.48 (meaning by 52%) since then, according to their latest report.
This analysis is the tenth ‘Living Planet Index’ from WWF and ZSL, but this year’s has a crucial difference from previous editions in that it is weighted to take account of the make-up of biodiversity in different areas. Previous versions treated every species on which data were available equally, whereas the new edition attempts to correct for the size of each taxonomic group in a region, for example by giving more weight to fish than mammals in the palearctic. The last index – published in 2012 – showed a 28% decrease between 1970 and 2008. The bleaker picture painted by the 2014 edition comes both from real declines in newer data, and from the new weighting.