Diversity on a Micro Scale

Microbes, which are tiny, microscopic living bodies, are the most diverse family of organisms on the planet, said Green, but we still don't know how microbial life varies across the surface of the Earth. "We had no idea whether or not this gradient of diversity from the tropics to the poles would hold for microbes," she said.

To find out, scientists collected ocean-dwelling bacteria from 57 sites around the world and discovered that there were, in fact, twice as many microbial species at the equator than at the poles, but they still couldn't say why.

So the team tested a couple of popular ecological theories. One claimed that higher levels of "primary productivity" (which is correlated with photosynthesis) in the tropical marine communities provides more energy, which in turn supports larger populations, leading to greater opportunities for variation over time. But a second theory suggested that temperature itself was more important for biodiversity.

Green's team provided the tiebreaker: They found that temperature, not primary productivity, led to increased biodiversity in microbes.

The equator's comparative diversity sparked the imaginations of many great early explorers, including Charles Darwin. This preliminary study merely scratches the surface of a new era of exploration, one that aims to understand biological variation not just for plants and animals, but for all life's domains.

- Chrisanne Beckner

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