No species lasts for ever, but the current rate of extinction is terrible

Biodiversity is crucial to the working of the ecosystems we humans rely on for our survival, says Kirsty Park

Dr Kirsty Park, The Guardian 15 Oct 08;

'Will the world and humankind be very much the poorer if we lose a thousand or so species?" asks Marcel Berlins (G2, October 8) in response to an International Union for the Conservation of Nature report revealing that 1,141 of the 5,487 known species of land mammal are at risk of extinction.

Berlins acknowledges that he is being deliberately provocative and would genuinely like an answer to this question. As a conservation biologist, I can provide one.

Berlins states: "I passionately believe in saving the whale, the tiger, the orang-utan, the sea turtle and many other specifically identified species." Leaving aside the false notion that there is a single species of whale or sea turtle, who gets to identify these lucky chosen species? On what basis? Berlins seems to confuse the relative importance of conserving any particular species with its emotional appeal to the wider public.

He continues: "What I do not accept is the general principle that all species alive today should carry on existing for ever. We have become so attuned to treating every diminution of animals, insects, birds or fish with concern that we have forgotten to explain why we think it so terrible."

No species exists for ever, and there is no principle that suggests any species should - extinction is a natural process, as the fossil record demonstrates. What is not natural is the rate of current extinctions in comparison to this natural "background" extinction rate. From documented extinctions alone (which are gross underestimates of the true number), the current rate is 100-1,000 times greater than the natural rate. Future extinction rates due to habitat destruction are predicted to be several times higher.

Berlins questions the "usefulness" of some species, saying: "Many species at risk are very close to other species that are not at risk; the differences are so small that only the scientists have any interest in them." Nature is incredibly complex and all species (including humans) are dependent on many others. Several studies have demonstrated that biological diversity is crucial to the sustained functioning of many of the ecosystems that humans rely on for food, materials, medicine, nutrient cycling, etc. It is very difficult to determine the precise detail of a species' "functional role", and impossible to judge with any certainty which species we can "afford" to lose.

There are countless examples of species that may look superficially similar to the casual observer but that are really quite different - the length of a bumblebee's tongue determines which floral species it pollinates, for example. You cannot just substitute one bumblebee species for another without risking the loss of large groups of flowers (including important economic crops) and all of the species that have symbiotic associations with those flowers.

Our preference for certain species bears no relationship at all to their "importance" in the ecosystem, or the morality of any human-induced extinction event. To borrow the words of Aldo Leopold, the great American ecologist: "The first rule of intelligent tinkering is to save all the pieces."

• Dr Kirsty Park is a lecturer in ecology and conservation biology at the University of Stirling