News Focus

On Rarity and Richness

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Science  12 Mar 2010:
Vol. 327, Issue 5971, pp. 1318-1319
DOI: 10.1126/science.327.5971.1318

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Microbes aside, upward of nine in 10 species crowd into the 30% of Earth's surface that's dry. It wasn't always that way, say a pair of researchers at the University of California (UC), Davis, who have been studying land and ocean features to understand how evolution proceeds in these two realms. At the Society for Integrative and Comparative Biology meeting, they argued that the difference in diversity is a recent phenomenon. Back in the Devonian period, 400 million years ago, the seas were home to an abundance of species, perhaps even more than on land. But about 110 million years ago, land plants went through a burst of speciation; so did the pollinators, fungi, and herbivores associated with them. These relationships made "rare" species possible, as plants acquired help in dispersing their pollen and seeds, resulting in relatively low population densities for individual species. Quickly, their numbers left marine biodiversity behind. The trigger for this terrestrial explosion, the researchers say, was the evolution of a more efficient way in which land plants use water.