CAMBRIDGE, Mass., July 20, 2010 -- The tropics owe their stunning biodiversity to consistent year-round temperatures, not higher temperatures or more sunlight, according to a novel survey of insect diversity at different latitudes and at different points in the planet's history.
The finding, presented this week in the journal Paleobiology by researchers from Harvard University, Simon Fraser University, and Brandon University, may finally answer a question that has dogged scientists for centuries.
It also suggests, intriguingly, that the world is likely far less diverse today than it was tens of millions of years ago, when the entire Earth had consistent year-round temperatures, much like the modern tropics.
"The latitudinal diversity gradient has been recognized for 150 years as one of the most general observations in nature, and has produced more explanatory hypotheses than nearly any other observation," says co-author Brian D. Farrell, professor of biology at Harvard. "We show that when most of today's organisms were diversifying, up through the Eocene, the world lacked pronounced seasonality, more like today's tropics, even in areas where the temperature was low."
"It appears it's not the heat of the tropics that promotes diversity; it's the newer seasons of the temperate zone that depress diversity."
Scientists' explanations for tropical biodiversity have tended to focus on the greater heat and light found closer to the equator, and to a lesser extent the low seasonality of the tropics, where average temperature in the hottest and coolest months may vary by only a few degrees.
"These factors tend to change together as you travel away from the equator toward the poles, leaving it difficult to separate their individual effects on diversity," says lead author S. Bruce Archibald, a research associate at Simon Fraser University, Harvard's Museum of Comparative Zoology, and the Royal British Columbia Mu
|Contact: Steve Bradt|