North American mammals are well on the way to mass extinction, and it's all our fault.
Each of the world's previous five mass extinctions wiped out more than three-quarters of all species on the planet. And now, North American mammals are one-fifth to one-half the way there, according to a University of California and Pennsylvania State University analysis.
It's been difficult for scientists to estimate how serious the current loss of species is because it's hard to compare species diversity today with the past.
The new analysis is based on combining data from three databases. One lists all mammal fossils and their geographic ranges in the United States between 40,000 and 500 years ago, and another which is a compilation of mammalian fossils dating from 40,000 to five million years ago. The third includes all fossil occurrences in the US between five and 30 million years ago. The databases include all terrestrial mammals from shrews to mammoths, except bats.
"The optimistic part of the study is that we haven't come all that far on extinction in the past 10,000 years," said co-author Anthony Barnosky, UC Berkeley professor of integrative biology. "We have this pulse when humans had their first effect about 13,000 years ago, but diversity has remained pretty steady for about 10,000 years."
The authors expect to see a similar pattern in Europe after the invasion of Homo sapiens some 40,000 years ago.
And the bad news is that we're still at it. In the last 100 or so years, says Barnosky, "We are seeing a lot of geographic range reductions that are of a greater magnitude than we would expect, and we are seeing loss of subspecies and even a few species. So it looks like we are going into another one of these extinction events."
"There is a bit of urgency here, Barnosky said. "By demonstrating that we have already lost 15 to 42 percent of mammalian diversity, the question is, do we really want to lose any more? I think the answer to that is pretty obvious."
The analysis appears in PLoS One.