The new study next examined evidence from the evolutionary family trees phylogenies of numerous plant and animal species. Phylogenies, constructed by studying DNA, trace how groups of species have changed over time, adding new genetic lineages and losing unsuccessful ones. They provide rich details of how species have diversified over time.
"The diversification rate is the speciation rate minus the extinction rate," said co-author Lucas Joppa, a scientist at Microsoft Research in Redmond, Wash. "The total number of species on earth has not been declining in recent geological history. It is either constant or increasing. Therefore, the average rate at which groups grew in their numbers of species must have been similar to or higher than the rate at which other groups lost species through extinction."
The work compiled scores of studies of molecular phylogenies on how fast species diversified.
For a third approach, de Vos noted that the exponential climb of species diversity should take a steeper upward turn in the current era because the newest species haven't gone extinct yet.
"It's rather like your bank account on the day you get paid," he said. "It gets a burst of funds akin to new species that will quickly become extinct as you pay your bills."
By comparing that rise of the number of species from the as-yet unchecked speciation rate with the historical trend (it was "log-linear") evident in the phylogenies, he could therefore create a predictive model of what the counteracting historical extinction rate must have been.
The researchers honed their models by testing them with simulated data for which they knew an actual extinction rate. The final models yielded accurate results. They tested the models to see how they performed when certain key assumptions were wrong and on average the models remained
|Contact: David Orenstein|