That would be 10 extinctions per 10,000 species per year, or 1,000 times the background extinction
The few species that seem to disappear in the uppermost Maastrichtian may constitute background extinction
pattern, or they could also be interpreted as the remaining Signor-Lipps effect.
Currently evolutionary theory is based almost exclusively on pattersn of background extinctions
, Jablonski says; scientists have assumed that mass extinctions simply accelerate or emphasize trends of background extinctions
so that the same kinds of organisms are wiped out by a mass extinction, only in much greater numbers.
At current levels of destruction, only 5 percent of tropical forests will remain in protected areas within 50 years, says the report, causing the rate of species loss to reach three or four orders of magnitude higher than the natural background extinction
rate of about one species each year.
To show the effect of introducing background extinction
into the process, we summarize the results of one typical simulation study in figure 5.
Both background extinctions
, which represent most extinctions in the history of life, and mass extinctions tend to be clumped into particular evolutionary lineages," Jablonski said.
So too does the author find Gould's accent on the caprice of mass extinctions "very plausible," along with its implied, attendant claim that such calamities are qualitatively distinct from run-of-the-mill background extinctions