As explorers investigated the world in centuries past they began pondering a puzzle called the ‘latitudinal diversity gradient’.
That’s science talk for: The farther you go from the tropics, the fewer different kinds of plants and animals there are. The question became, is it because more species originate in the tropics, or because older ones can persist there longer? In other words, are the tropics a cradle of diversity or a museum? The answer: It’s both.
A team of palaeontologists studied a large group of marine animals - oysters, clams, scallops and other bivalve molluscs. About three-quarters of today’s types of these creatures originated in the tropics and spread outward toward the poles, while only one-quarter originated at higher latitudes, they report in Friday’s edition of the journal Science.
The researchers found that as they traced the marine animals back in time over an 11 million-year period there was a consistent pattern with twice as many originating in the tropics as other areas. And while only 30 varieties that lived only in the tropics went extinct, 107 that lived outside the tropics died out.
“I think we’ve killed the idea that the tropics are either a cradle or a museum of biodiversity. They’re both,” said co-author James Valentine, professor emeritus of integrative biology at the University of California, Berkeley.
“The tropics are the engine for global biodiversity,” added co-author Kaustuv Roy, associate professor of biology at the University of California, San Diego.