Researcher expands on theory of tropics as biodiversity cradle

The University of Chicago evolutionary expert has refined his theory that the tropics is the key to the biodiversity in the world today.

He is David Jablonski. and much of his study is based on the marine bivalves, clams, oysters and similar.

He studies these because they leave a strong record in fossils and because there are about 8,000 species throughout the world.

An article by the University of Chicago said Monday that  Jablonski has added another chapter to his out of the tropics theory.

That’s a play on words mimicking the out of Africa theory about the development and dispersion of humans.

In research to be published this week, Jablonski describesbridge species that are found in the tropics and also in cooler climates.

In 2006 Jablonski first establishes that most of the marine bivalve lineages worldwide that first appeared in the past 11 million years did so in the tropics.

This suggests that, besides having the most species, the tropics are likely the primary source of diversity elsewhere on Earth. Reported the university:

“The new research corroborates the out of the tropics model that Jablonski and others introduced in a 2006 publication. In fact, the new study documents this dynamic over the past 12 million years — even during the Ice Ages, when the temperature differences between the equator and the poles became more severe. That runs counter to the broadly accepted principle of niche conservatism, which suggests that related species tend to retain the ecological limits of their ancestors, Jablonski said. ‘Most species we studied do adhere to that principle, but the ones that do not are crucial to the deployment of biodiversity on Earth.’

“There are many such bridge species but each evolutionary lineage generally has only one or two. Therefore, bridge species are widespread in an evolutionary sense but rare in terms of overall biodiversity, according to the research. And the fossil record shows that most of today’s bridge species started as tropical species. ‘Somehow they left their tropical cradle, adapting to the colder temperatures and more variable climates of the temperate zones,’ said Jablonski. ‘It’s impressive that they apparently expanded their ability to tolerate these harsher conditions.’

The research is not without a warning.  Jablonski notes that a crisis in the tropics, such as pollution or over exploitation, would have great impact all over the world.

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