Randolph E. Schmid, Associated Press
March 15, 2007 — Do more species develop in warm, tropical climates or cooler, temperate areas? It turns out the longtime answer — the tropics — may be wrong.
True, more different types of animals exist there than in places farther from the equator.
But new research suggests that is because tropical species do not die out as readily. Cooler regions have a higher turnover rate, with more species developing but also more becoming extinct.
"It's a surprising result," Jason T. Weir of the zoology department at the University of British Columbia said in a telephone interview.
The findings by Weir and Dolph Schluter are published in Friday's issue of the journal Science.
They compared sister species from the Americas. Sister species are the most closely related species that share a common ancestor.
By analyzing the DNA of 618 mammal and bird species that lived in the past several million years, they were able to determine that new species develop more readily farther away from the tropics.
"It would take one species in the tropics 3 to 4 million years to evolve into two distinct species, whereas at 60 degrees latitude (two-thirds of the way toward either pole), it could take as little as 1 million years," Weir said.
"In other words, there's a higher turnover of species in places like Canada, making it a hotbed of speciation, not the Amazon," said Schluter.
That, however, is balanced by a higher extinction rate in colder climates, so the tropics still have more diversity.
It also raises the question of whether a more variable climate causes more rapid evolution.
