Category: Biodiversity

Biodiversity and Mr. Gradgrind

If someone were to ask you how many plants and animals are known to have become extinct since the year 1600, I wonder what you would answer. The general impression given by our media is that human development, including agriculture and hunting, has had a devastating effect on wildlife all round the world. In reality, the figure is tiny, being about 1030, of which 110 were mammals, 103 birds, and 396 higher plants (ferns and flowers).

Even if we do not include viruses and bacteria, we have no accurate idea of the total number of species that might exist today. Estimates range from a low of 2 million to 14 million, and then upwards to a mind-boggling extreme of 80 million. To date, only 1.6 million of these have been physically counted and recognized. If we take the lowest of these estimates, it would still only give us an approximate extinction rate of 0.006 per cent every 50 years. Moreover, this low extinction rate must be offset by the evolution of new species (which we know is happening) and by the fact that species once believed to have been lost forever are being constantly re-discovered. In the Atlantic forests of Brazil, for example, a number of species thought to have become extinct 25 years ago, including six butterflies and several birds, have been re-found recently. And, with much publicity, the ivory-billed woodpecker (1), declared extinct in 1920, has just been spotted in the Big Woods of eastern Arkansas. So the corrected extinction rate will be much less – indeed, for all we know, it might even be negative. Now that is a thought – I bet that doesn’t get into the press!

Yet, for some time now, Green activists have wanted us to believe that we are losing in the order of 40,000 species every year, or 109 species a day. Former US Vice-President, Al Gore, repeated this figure in his book, Earth in the Balance (1992). Amazingly, however, even this hype has now been topped by the media response to a recently-published scientific paper which gave rise to sensational headlines, the broadsheets outdoing each other in their tabloid-like frenzy: “Over a million species will be doomed to extinction owing to the effects of global warming.”

But, as always, the devil is in the detail. It may thus come as a surprise to those of you who were shocked by such lurid headlines to learn that the original study, entirely valid within its own terms, was based on only 1,103 species that were selected from a number of regions around the world – 243 were South African members of a plant family called the Proteaceae, which has some 1,000 species in all. Using, in this instance, the widely-employed media estimate of 14 million species, this would mean that the research sampled 0.008 per cent of the total species on the planet. But, as I have already indicated, we have no idea of the validity of such an estimate. What the original research showed us is that, if the selected climate model were to be correct (an enormous caveat, of course), some 15 to 37 per cent of the 1,103 chosen species, in certain habitats, may be under threat. The rest is virtual extrapolation and speculation – and unfettered media hype. So we have moved, at the flick of a computer button, from around 400 species, or less, to 1.25 million extinct species and to ‘Apocalypse Now’.

Happily, you don’t have to be a scientist to see the flaws in all of this. Common sense is a mighty powerful tool when one is confronted by doomsday headlines. First, if you change the climate model employed, the outcome will be radically altered. There are hundreds of possible scenarios for future climates, and, if you do want to rid the ‘virtual’ Earth of millions of species at the click of a mouse, then try the ‘We-Are-Plunging-Back-Into-An-Ice-Age’ model. Your computer screen should then coldly display mammoth extinctions on a global scale. Secondly, if you adjust the range of plants and animals selected for study, you will likewise achieve a different outcome, and choosing the tiny beasties, from viruses to insects, might well give you an overall increase in biodiversity, certainly for some parts of the globe.

Thirdly, as was most perceptively pointed out by the New York Times of all newspapers, this type of analysis is usually based on a number of steady-state assumptions, such as the ways animals might migrate and respond to climate change. Charles Darwin would have credited the organisms with more dynamic, adaptive nous. Fourthly, the whole approach tends to rest on a biological construct called the ‘species-area relationship’, which is not as robust a model as one might think when approaching the study of extinctions. This construct is used to argue that smaller habitat areas support fewer species. But, as a number of commentators have pointed out, there are many other factors involved. On the island of Puerto Rico, for example, a 99 per cent loss of primary forest cover did indeed cause the loss of 7 out of 60 species of bird, although the whole process of deforestation augmented the total bird numbers on the island to 97, thus increasing the overall biodiversity. Things are never simple.

We should thus ensure that over-enthusiastic media extinction claims become as dead as the proverbial dodo.