The Science study underscores the need to avert a tropical diversity crises, its authors said.
"Human-caused extinctions in the tropics will eventually start to affect the biological diversity in the temperate and high latitudes," Roy said. "This is not going to be apparent in the next 50 years, but it will be a long-term consequence."
Noted Valentine: "We should preserve the tropics, because without them, we've lost a key source for diversity in higher latitudes."
The fossil record indicates that the tropics have enjoyed a richness of biodiversity spanning at least 250 million years. Jablonski compared the population of species on Earth to the population of a modern town. To understand how that population mix came about would entail an examination of birth records, cemetery records and immigration records.
The team acquired its data for the Science study by analyzing bivalves, a class of marine life that includes clams, scallops and oysters. "They live everywhere," Jablonski said. "They're found from the Arctic Ocean to the hottest part of the tropics, and they have left a great fossil record."
This record permitted the team to track more than 150 bivalve lineages back through time and answer a series of key questions: Where do they start? How long do they last? Where do they persist? And where do they spread?
As the paleontologists traced the lineages back into geologic time, they found a consistent pattern in each slice of time, regardless of the prevailing climatic conditions. Over the entire 11-million-year period, they found that more than twice as many bivalve lineages started in the tropics than at higher latitudes. M
Contact: Steve Koppes
University of Chicago