According to a study published in today’s issue of Nature, preserving the earth’s biodiversity is not just a nice idea—it is necessary to ensure ideal functioning of the planet’s ecosystems. Michel Loreau of the Ecole Normale Superieure in Paris and Andy Hector of Imperial College in London analyzed data collected from BIODEPTH, an international experiment run on more than 500 grassland sites located in seven European countries, to calculate the relative importance of complementary interactions between plant species.
In the mid-1990s, researchers planted BIODEPTH sites with varying numbers and types of plant species and functional groups— classifications used by ecologists to describe the role species play in an ecosystem—to mimic the effects of species extinction. Loreau and Hector, borrowing techniques from evolutionary genetics, devised a new equation to isolate the effects of two competing mechanisms to explain the effects of species diversity on ecosystem productivity. The first, the "sampling," or "selection," effect, states that as the number of species increases, the probability that a random sample will include a more productive species also increases. In other words, certain individually productive species are what's important. The second effect is based on species complementarity—it says that the more species present, the more likely it is that cooperation between species will lead to the most efficient use of resources.
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