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Island species are more vulnerable to extinction
on 17 May 2005
David Quammen can't tell us about the song of the dodo because it's a too late. The bird is extinct - they were all exterminated by 1690. Dodos were an island species - a big, flightless sort of pigeon. Sailors despised their apparent 'stupidity'. This stupidity or 'tameness', as we might also mistakenly think of it, is now recognised by modern naturalists as the naivety of animals that live on islands, which results from having no previous experience of predators. They didn't know they should avoid people or run away when approached, so it didn't take long to kill enough of them to ensure their extinction. Introduced species helped to bang the last few nails into the dodos' coffin lid. David Quammen could hardly have chosen a more symbolic creature than the dodo, for the title of his book on "island biogeography in an age of extinctions".
The author has a nice, laid-back writing style and has arranged some uncomfortable facts into an easy read. Here's an example. The voracious appetites of growing populations and industry put our natural environment under enormous pressure and cause habitats to be destroyed or divided into smaller and smaller pieces. So he asks us to imagine a fine Persian carpet - then to imagine it being chopped into pieces. What would happen? The edges would unravel and the bits that were left wouldn't be nearly so useful or so beautiful as the whole carpet had been. That's what happens to ecosystems when they're chopped into small pieces, like 'islands'. They unravel and decay. Island biogeography used to be just about proper islands - the sort that are surrounded by water - but it's now applicable to the islands scattered within continents. Continents have been criss-crossed by roads and rails, buried under cities, industrial estates, farms, quarries and so on, leaving tiny pockets of natural habitat isolated from other natural areas, like islands in a sea of agriculture or urban sprawl. From the point of view of the animals and vegetation that still manage to exist in these 'island' patches, the surrounding areas amount to a barren waste that cannot be crossed.
Quammen is understandably critical of the destructiveness of our species. He refers to the 'background' rate of extinction and the 'normal' rate of extinction, meaning: what the rate of extinction would be if it were not being driven by Homo sapiens. He says, for instance, it's estimated that the rate of extinction of birds and mammals alone, is about one hundred times the background level. And if that figure isn't staggering enough, he points out that Edward O Wilson's studies suggest the current loss of rainforest species, particularly invertebrates, is "at least a thousand times above normal". Quammen believes it would take this planet's ecosystems ten or perhaps even twenty million years to recover to previous high levels of diversity, if our species were to stop driving up extinction. He says that the difference between a normal extinction rate and the present human driven extinction rate is like the difference between having a pilot light permanently burning in the basement furnace and the house being on fire.
It's a big book (almost 700 pages), packed with interesting stories and information. There are ripping yarns (all true and documented!) about the intrepid chaps who started it all: Charles Darwin and Alfred Russel Wallace. And there are stories of the scientists who are working on island biogeography today, that are just as hair raising. I recommend this book to everyone who's interested in natural history and the environment.