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Study Deems Tropical Areas Both Cradle and Museum of Biodiversity

You probably know that the world's tropical areas - on land and in the water - are the most biologically diverse places on earth. The fact is there are simply more different life forms near the equator than there are near the poles. But the question is why.

For more than a century, biologists have tossed out competing theories as they debated the reason for the abundance of species in the regions near the equator.

"Are the tropics where all biodiversity originates? Or are the tropics where biodiversity accumulates because the tropics are such relatively stable, benign habitats? So that's what the real fight has been about," says Prof. David Jablonski of the University of Chicago. He and his colleagues set out to settle the debate once and for all.

"And so what we want to do is take a really fresh look at this problem by using the fossil record to pin down both origination - the start of new lineages - and extinction - the persistence of new lineages," said Jablonski. "And now, here's the real key to it all. We wanted to look at how lineages spread over time."

In a paper published this week, Jablonski says they figured it out.

"It turns out that the fight was about a false distinction. Instead, it turns out the tropics are both a cradle and a museum of biodiversity. Our fossil record really pretty clearly shows that lineages do indeed start in the tropics and spread out over time, but they stay in the tropics, too. And so that means the tropics are not only the generator of biodiversity, but they're also an accumulator simultaneously."

To come to their conclusion, the researchers studied the fossil record left by species of bivalves - animals like clams, oysters and mussels. It's an abundant group well represented in museum collections. Jablonski and his colleagues traveled the world to study bivalve fossils in museums - not the exhibits that we would see if we visited, but the research materials curators keep in drawers and cabinets, out of public view.

"Museums are an absolute scientific treasure trove," stressed Jablonski. "They're still being underutilized in terms of the fantastic set of information that we can extract from those museum collections. They represent information that we could never get any other way. And so it was a gold mine for the kinds of work that we were trying to do."

There are many theories to explain the rich biodiversity in tropical areas, compared with colder latitudes. The University of Chicago paleontologist says understanding what scientists call this Latitudinal Diversity Gradient could be key to managing the planet's vital biodiversity.

"It is the single most overarching, major pattern of biological diversity today, and probably deep into the geological past. And one result that our analyses show is that destruction of biodiversity in the tropics will have a truly global impact."

David Jablonski's paper on biodiversity in the tropics was published Friday in the journal Science.