(Image: Andrzej Krauze)
SOME 鈥渇acts鈥� are just too good to check. You might hope science would be immune from this sort of pitfall, but it seems not.
In much of ecology, it is taken as read that invasive species were a major culprit in recent extinctions. This is widely stated, despite a lack of evidence for it. While doing research for my latest book, I found the claim being passed on in ways reminiscent of Chinese whispers.
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The UK government鈥檚 Non-native Species Secretariat (NNSS) declares that 鈥�. Its source is the report, published in 2006 by the secretariat of the UN Convention on Biological Diversity (CBD).
They, in turn, say the stat came from a by Cornell ecologist David Pimentel, who was in turn drawing on a by David Wilcove, now at Princeton University.
As is clear from the paper鈥檚 title, 鈥淨uantifying threats to imperiled species in the US鈥�, Wilcove was not talking about actual extinctions but an extinction threat, and in the context of the US (in fact, his data largely related to Hawaii). Wilcove told me his paper was being misused. Although informed of this, the NNSS has kept the claim on its website.
The claim is absent from the most recent Global Biodiversity Outlook report, issued last year, but has been replaced with: 鈥淪pecies introduced into new environments鈥� have contributed to more than half of the animal extinctions for which the cause is known.鈥�
The report cites a 2005 in the journal Trends in Ecology & Evolution, by Miguel Clavero and Emili Garcia-Berthou of the University of Girona, Spain. But that turns out to be just four paragraphs long.
It reports, but gives no details of, an analysis of a quarter of the 680 extinct species in an International Union for Conservation of Nature (IUCN) database.
This work was a riposte to a rather longer by Jessica Gurevitch and Dianna Padilla of Stony Brook University in New York, who looked at the same IUCN database and concluded that just 2 per cent of all extinctions had alien species listed as a cause.
I could go on. Suffice it to say that Gurevitch and Padilla may have been on to something when they concluded that 鈥渁vailable data supporting invasion as a cause of extinctions are, in many cases, anecdotal, speculative and based upon limited observation鈥�.
It seems that even in science, sometimes the facts aren鈥檛 allowed to get in the way of a good story.
This article appeared in print under the headline 鈥淭rial by repetition鈥�
