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ducted during a two-year period by 34 researchers in eight European countries. This time, the results were more persuasive. They showed once again that productivity does increase with biodiversity. Many of the experimental runs also revealed the existence of overyielding. Over millions of years, nature's ecosystems engineers have been especially effective in the promotion of overyielding. They have coevolved with other species that exploit the niches they build. The result is a harmony within ecosystems. The constituent species, by spreading out into multiple niches, seize and cycle more materials and energy than is possible in similar ecosystems. Homo sapiens is an ecosystems engineer too, but a bad :;; one. Not having coevolved ~ with the majority of life ~ forms we now encounter 8 around the world, we eliminate far more niches than we create. We drive species and ecosystems into extinction at a far higher rate than existed before, and everywhere diminish productivity and stability. I will grant at once that economic and production values at the ecosystem level do not alone justify saving every species in an ecosystem, especially those so rare as to be endangered. The loss of the ivorybilled woodpecker has had no discernible effect on American prosperity. A rare flower or moss could vanish from the Catskill forest without diminishing the region's filtration capacity. But so what? To evaluate individual species solely by their known practical value at the present time is business accounting in the service of barbarism. In 1973, the economist Colin W. Clark made this point persuasively in the case of the blue whale. Balaenopterus musculus. About 30

To evaluate individual species solely by their known practical value at the present time is business accounting in the service of barbarism .... Of the species known, fewer than one percent have been studied beyond the sketchy anatomical descriptions used to identify them.

A blue whale glides through the eastern tropical Pacific Ocean. Overjishing caused the population to plummet from hundreds of thousands to a few hundred in the 1970s. They remain injeopardy because quick projits are still pitted against conservation for long-term benejits.

science), that the increase in production in particular is truly the result of just an increase in the number of species? Maybe the effect is due to some other factor that just happens to be correlated with species numbers. Perhaps the result is a statistical artifact. For example, the larger the number of plant species present in a habitat, the more likely it is that at least one kind among them will be extremely productive. If that occurs, the increase in the yield of plant tissue-and in the number of the animals feeding on it-is only a matter of luck of the draw, and not the result of some pure property of biodiver-

sity itself. As its base, the distinction made by this alternative hypothesis is semantic. The increased likelihood of acquiring an outstandingly productive species can be viewed as just one means by which the enrichment of biodiversity boosts productivity. (If you draw on a pool of 1,000 candidates for a basketball team, you are more likely to get a star than if you draw on a pool of 100 candidates.) Still, it is important to know whether other consequences of biodiversity enrichment play an important role. In particular, do species interact in a manner that increases the growth of either one or both? This is the process called overyielding. In the mid-1990s, a massive study was undertaken to test the effect of biodiversity on productivity that paid special attention to the presence or absence of overyielding. Multiple projects ofBlODEPTH, as the project came to be called, were con-

Profile for SPAN magazine

SPAN: July/August 2003  

An American Gharana?; Digital Railroad to Fly; Think Tanks & U.S. Foreign Policy; Can Economic Diplomacy in South Asia Work?; Muscle & Magic...

SPAN: July/August 2003  

An American Gharana?; Digital Railroad to Fly; Think Tanks & U.S. Foreign Policy; Can Economic Diplomacy in South Asia Work?; Muscle & Magic...

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