Is Another Mass Extinction Imminent?

Candice Gaukel Andrews by Candice Gaukel Andrews | September 27th, 2012 | 2 Comments
topic: Green Living

Pronghorn in Yellowstone National Park

We could be on the brink of a mass extinction — the Earth’s sixth — according to a paper published last year in the journal Nature. First author Anthony Barnosky, an integrative biologist at the University of California at Berkeley, says Earth has experienced five mass extinctions during the past 540 million years, and another extinction could be around the corner. During each of the five previous events, three-quarters or more of the world’s animal species died out. One of the mass extinctions — which occurred 65 million years ago — ended the dinosaurs.

Some say, however, that this isn’t much cause for alarm. Species have always come and gone over long periods of time; and given the five mass extinctions we’ve already had, it’s a natural event. But will this sixth one be a “different animal”? 

The sixth is under way

Frog

The amphibia class has been on the decline for some time. Frogs, in particular, have suffered, having lost an estimated 170 species in the last 10 years, with another 1,900 threatened. ©Cassiano Zaparoli (Zapa)

Barnosky and his colleagues looked at fossil records and calculated the rate at which mammals died off in the past 65 million years. They found an average extinction rate of less than two species per million years. But in the past 500 years, a minimum of 80 of 5,570 species of mammals have gone extinct, a rate above documented rates for past mass extinctions. This means that we’re at the beginning of one.

The situation looks even more dire when all mammals currently classified as endangered or threatened by the International Union for Conservation of Nature (IUCN) are added to the count. If all of those animals disappear within a century, then 334 years from now, 75 percent of all mammal species will be gone. The team extended the same methods of analysis to amphibians, reptiles, birds, plants, mollusks and other forms of life. They found fairly consistent patterns.

H. Richard Lane, program director of the Division of Earth Sciences at the National Science Foundation, which funded this research, says that unlike the previous global mass extinctions, the sixth will be the result of climate change caused by human activities. Conservationists have warned for years that we are seeing a massive, human-caused extinction, with species from frogs to birds to tigers threatened by global warming, loss of habitat and competition for resources with introduced nonnative species.

On the upside

Others, however, point out that Barnosky’s research is based on observations from just a very few “twigs” (the IUCN’s Red List) plucked from the tree of life. And so far, only 1 to 2 percent of all species have gone extinct in the groups looked at in Barnosky’s study. Too, fossil dating is not a precise science, and the fossil records and modern data collected by conservation biologists don’t always match up well. And assuming threatened species will actually go extinct is a problem, since it’s not inevitable.

In addition, the number of unknown species may be in the millions or tens of millions — many times that of what has been discovered. That makes any percentages of how many of the world’s species are in trouble unreliable.

Still a lot to save

But co-author Charles Marshall, also an integrative biologist at UC-Berkeley and director of the university’s Museum of Paleontology, emphasized that the small number of recorded extinctions to date (1 to 2 percent) does not mean we are not in a crisis. He believes that just because the magnitude is low compared to the biggest mass extinctions Earth has seen in half a billion years doesn’t mean it isn’t significant.

Tiger

There may be only 3,200 tigers left in the wild, according to the World Wildlife Fund. ©Toby Sinclair

Despite that, all is not gloom and doom, per the paper’s authors. It’s not too late, they believe, to save endangered animals — and stop short of the tipping point. Of course, that would require dealing with a unique mix of modern threats, including habitat fragmentation, invasive species, diseases and global warming.

Luckily, we’ve still got a lot of biota left to save.

Do you think we’re on the brink of a human-caused mass extinction? Or are such events just a cyclical part of nature? If we are at the threshold, will this mass extinction be more devastating than the ones in the past?

Happy trails,

Candy

Feature photo: More than 80 percent of plant species in grasslands contribute to their effective functioning. Loss of biodiversity puts our environments in jeopardy. This pronghorn buck and doe were photographed in a grassland in Yellowstone National Park. ©Henry H. Holdsworth



Comments

  1. The “Happy trails” sign-off is really apt in this article. I’m enjoying my coffee a little more than I otherwise would right now.

    It’s funny to think about extinction. I feel confronted with global warming on a daily basis but rarely meditate on the end result.

    Travis | September 27th, 2012 | Comment Permalink
  2. We are not on the brink of a human induced mass extinction, we are in the midst of it. It has been happening for several thousand years, and is very unlikely to slow down. We should have no delusions, extinctions will continue, will probably accelerate, until the human population starts to decline. The only things that will be changed will be the identity of species that become extinct. In the past (paleolithic), it was the mega-fauna, now we can conserve a selection of larger species in zoos etc.. Meanwhile hundreds of other species will disappear. Its very simple, for every extra cow, goat or human that appears on the planet, and equivalent biomass will disappear. For every new acre of soya, maize, oil palm etc, another acre of forest, grassland etc will disappear and all its biodiversity. Anyone who thinks otherwise is deluded.

    John | November 2nd, 2012 | Comment Permalink

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