More than four decades ago, field ecologists set out to quantify the diversity of trees on a forested plot on Barro Colorado Island in Panama, one of the most intensively studied tracts of tropical forest on the planet. They began counting every tree that had a trunk wider than a centimeter. They identified the species, measured the trunks, and calculated the biomass of each individual. They put ladders up the trees, examined saplings, and recorded it all in sprawling spreadsheets. As they looked at the data accumulating year after year, they began to notice something odd. With some 300 species, the tree diversity on the tiny 15-square-kilometer island was staggering. But the distribution of trees among those species was also heavily lopsided, with most of the trees belonging to only a few species. Since those early studies, that overstuffed, highly uneven pattern has been seen repeatedly in ecosystems around the world, particularly in rainforests. The ecologist Stephen Hubbell of...
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