Are WWF doing things by halves? (2)

The recently released WWF report claims that “in less than two human generations, population sizes of vertebrate species have dropped by half” but what does it really mean? In the previous post I showed that the jump in “population sizes” from 28% reported by WWF in 2012 to 52% in 2014 was due to a change in the assessment methodology. Does anything else in the WWF report look dodgy?

Well, I am a bit puzzled by the way WWF are counting the animals. If I understand their statistical methodology correctly they do not tally up all vertebrates alive to track how the total has changed over the last 40 years. What they do instead is look at the individual “populations” understood as species inhabiting a certain geographical area. For the 2014 report they assessed 10,380 populations belonging to 3,038 species to see what had changed since 1970. They then assign different “weighting” to the ratios of gain & loss for the groups of populations to (quoting from the report):

account for the fact that the population trends for each taxonomic group and biogeographic realm in the LPI database are not a perfect representation of the number and distribution of vertebrate species that exist in the world.

The tables of weightings for the taxonomic groups are as follows:


But the data manipulation does not end here as the sub-totals from different realms are then weighted to produce the bottom-line average population size change. The weightings table for the realms is as follows:


When I see complex tables full of numbers used as input I instinctively distrust the output. Why is the weighting of mammals 10% of the birds weighting in the tropics but 40% in the Antarctic? I do not doubt that there is some justification for the weightings WWF have used but I am equally sure that substantially different numbers could just as easily be justified.

It is also intriguing how they have accounted for the farm animals. Some news items imply the WWF report is a headcount of wildlife only:

Half of Global Wildlife Lost, says new WWF Report

Earth has lost half of its wildlife in the past 40 years, says WWF

Does it mean that the cows, chicken and pigs have not been counted? So if an area of bog has been drained and converted to dairy farming we are lamenting the demise of frogs rather than celebrating that more cows produce more milk to feed the kids?

But perhaps I am just being paranoid and the report’s claims are actually well justified. What do others have say about the WWF conclusions? Let us start with the comments by Stuart Pimm, a biology professor at Duke University and prominent expert in animal extinction:

What it shows is that the variety of life on earth is in trouble — and that broad conclusion is absolutely correct, but the problem with this particular index is that it lumps all sorts of things together, and doesn’t do it in a way that is terribly helpful. (…) [The notion of “critical tipping points” suggested in the report] is a complete fabrication. It’s an attempt to grab attention to a particular view of the world. There is simply no evidence that there is some point below which biodiversity cannot go.

And now a succinct quote from an opinion piece by Ivo Vegter:

Even if the recent claim by the WWF, that the world’s animal population has declined by 52% since 1970s, were true, it would be a misleading statistic to report. Masters at fund-raising propaganda, the WWF turned out a gem of quotable nonsense.

As usual, one should make one’s own mind who to believe.



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