Humans have increased animal extinction rates by 1,000 times

(NaturalNews) The current global extinction rate is 1,000 times higher than it was before humans came along, according to a study conducted by researchers from Brown University, Duke University, Microsoft Research and the University of Georgia, and published in the journal Conservation Biology.

"We've known for 20 years that current rates of species extinctions are exceptionally high," senior author Stuart Pimm said. "This new study comes up with a better estimate of the normal background rate -- how fast species would go extinct were it not for human actions. It's lower than we thought, meaning that the current extinction crisis is much worse by comparison."

Ten times worse than previously thought

Biologists agree that the earth is currently in the midst of the sixth mass extinction event in its history. But even knowing current extinction rates, it isn't possible to gauge the severity of the current crisis without understanding what the normal extinction rate is supposed to be. The new study revises an earlier estimate by Pimm in the 1990s, adjusting it upward by an order of magnitude.

Previously, Pimm had estimated that the extinction rate 60 million years ago was approximately one extinction per million species per year. The new estimate shows that extinctions were actually significantly less frequent than previously believed, at a rate of only 0.1 per million species per year.

The current extinction rate is approximately 100 per million species per year. That means extinction rates are now 1,000 times the normal, "background" rate.

In order to improve on prior estimates, the researchers used three different models for calculating background extinction rates. As in prior studies, one of those models involved examining fossil records. The limitation of this approach is that fossils tend to over-represent hard-bodied sea animals and can make identification of individual species difficult.

The second model involved studying DNA to trace how lineages of different plants and animals have changed over time. Tracking rates of genetic change can show the rate at which species have diversified into new forms.

"The diversification rate is the speciation rate minus the extinction rate," co-author Lucas Joppa said. "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 third model involved studying the rate at which species diversity has increased in recent geological history. New species tend to proliferate rapidly before many of them go extinct.

"It's rather like your bank account on the day you get paid," de Vos said. "It gets a burst of funds -- akin to new species -- that will quickly become extinct as you pay your bills."

By comparing rates of proliferation of new species with historic (lower) rates of species proliferation, researchers can get a sense of how many species tend to naturally go extinct over time.

All three models consistently delivered a background extinction rate of 0.1 species per million per year, even when researchers deliberately inserted key faulty assumptions. This shows the robustness of the models used.

Urgent measures needed

In another recent study published in the journal Science, Pimm, Joppa and colleagues found that human consumption of resources was the primary factor driving species extinct, placing them in danger of extinction or confining them to small ranges of land.

The new study shows that the human-driven extinction crisis is even more dire than previously believed, Pimm said.

"This reinforces the urgency to conserve what is left and to try to reduce our impacts," de Vos said. "It was very, very different before humans entered the scene."

Sources for this article include:

https://news.brown.edu

http://onlinelibrary.wiley.com