Soon to be gone - Endangered Species

by: Jessica Ward - January 2005

With regard to your question about the current rate at which we are losing species worldwide, the short answer is that nobody really knows. As a M.Sc.candidate in biology, I have attended several talks on this topic including one by Lord Robert May (Chief Scientific Adviser to the British Government). In recent scientific discussion of this question, our inability to accurately answer it has largely been attributed to the fact that we still don't even know how many species there ARE (estimates run from about 5 to 80 million or more).

The preface of the book "Extinction Rates" (edited by John Lawton and Robert May, Oxford University Press, 1995) states that "tropical deforestation is extinguishing roughly one species every hour, or maybe even one every minute". Since these rates are estimated from only one cause of extinction in one environment (tropical deforestation), the total rate must be far greater.

In his book "The Future of Life" (published by Alfred A. Knopf, 2002), Edward O. Wilson states that extinction is today "between one and ten thousand times the rate before human beings began to exert a significant pressure on the environment". This is a bit misleading, though, since extinction rates have certainly varied throughout the Earth's history (see http://www.af-info.or.jp/ eng/honor/gif/2001/03-e.jpg for a graph), so this statement is really based on an average across tens of millions of years. He then goes on to explain how different methods used by biologists to estimate current rates of extinction produce different numbers (starts on page 99 if you can find a copy of the book). In summary, estimates based on counts of actually observed extinctions in well-studied groups like birds and flowering plants, as well as estimates based on the IUCN Red List which take into account those species thought to be "committed" to extinction in the near future, are too low because they fail to consider acceleration in extinction rates due to the intensification of extinction causes nor can they possibly account for the extinction of undiscovered or understudied species. Three other methods have all estimated current extinction rates as one thousand to ten thousand species per million per year. These methods are based on (1) species-area relationships and current rates of habitat destruction, (2) tracking the descent of species through the IUCN Red List categories over time, and (3) population viability analysis (PVA).

E. O. Wilson goes on to state that "If the decision were taken today to freeze all conservation efforts at their current level while allowing the same rates of deforestation and other forms of  environmental destruction to continue, it is safe to say that at least a fifth of the species of plants and animals would be gone or committed to early extinction by 2030, and half by the end of the century. If, on the other hand, an all-out effort is made to save the biologically richest parts of the natural world, the amount of loss  can be cut by at least half".