Extinction and evolution are more complicated than formerly assumed

The extinction of species may be a slower and more complex process than scientists at one time expected. Many species find ways to prolong life and even make small comebacks from near-extinction. Species' doggedness at hanging on has become an embarrassment to many ecologists and conservation biologists.

Two decades ago in such studies as the Global 2000 Report, experts were predicting that some 20 percent of the world's species at that time would be extinct by now, mostly because of the human impact on the environment. That hasn't happened, causing scientists to question the methods used to predict extinction.

The main tool now is the species-area curve, which gives an estimate of species lost for a given area of habitat destroyed. Another uses computer models to project trends in a range of conditions affecting isolated populations of a species and calculate the probability of long-time survival.

Some biologists stress that concern over the current turmoil in the natural world should be tempered with the awareness that change – including extinctions and new bursts of speciation – is an essential part of the ferment of life on earth.

Puerto Rico, which lost 97 percent of its forests, is almost completely forested again, with a mix of exotic and native species.

The Gingko tree was nearly extinct in China, and now has spread around the world.

A research and recovery programme may have brought the Puerto Rican parrot back from a total of only 14 birds in the 1970s.

Meanwhile, evolution may be a faster process than once thought. In 1937, sockeye salmon were introduced into a lake near Seattle. In 1992, researchers discovered that the original stock has evolved into two different groups of salmon with slightly different genetic make-ups. The two had stopped interbreeding, the first step toward becoming different species.

Source: Andrew C. Revkin, "Extinction Turns Out To Be A Slow, Slow Process," and Carol Kaesuk Yoon, "Scientists' Hopes Raised for a Front-Row Seat to Evolution," New York Times, October 24, 2000.

For text http://www.nytimes.com/2000/10/24/science/24EXTI.html and http://www.nytimes.com/2000/10/24/science/24SPEC.html

For more on Biodiversity http://www.ncpa.org/pi/enviro/envdex5.html#g