Deforestation, climate change and the dramatic impact human societies have had in reshaping the Earth for the past few thousand years are taking an extraordinary toll on its animal species, which are dying off about 1,000 times faster today than they did before humans arrived.
It all adds up to the sixth mass extinction in the planet's history, the editors of Science Magazine report in a special series of scientific studies released Thursday, which both explore the implications of "anthropocene defaunation" and offer prescriptions for how we might re-colonize animal populations throughout the world.As one study pointed out, over the past four decades Earth's human population has roughly doubled, while during the same period the number of invertebrate species -- like insects, worms, spiders, clams, snails and starfish -- has shrunk by about 45 percent.
"We were shocked to find similar losses in invertebrates as with larger animals, as we previously thought invertebrates to be more resilient." Ben Collen, a research scientist with the U.K.-based University College London and one of the study co-authors, said in an interview with USA Today.Scientists point out that extinctions of individual species aren't uncommon, as more than 99 percent of all the known species ever to have existed on Earth are now gone forever.
What has changed is the speed with which species are going extinct, a phenomenon scientists chalk up to the impact humans have had on the planet for the past two centuries. Many argue we should call the age we're living in the "Anthropocene," or the Age of Man.
That's because the impact humans are having on the planet and its ecosystems -- killing off species by destroying their habitats for building cities and agriculture, hunting them and overfishing them to extinction, and by the industrial pollutants we pump into the atmosphere, and into our lakes, rivers and oceans -- are so dramatic that they constitute a definable geological time scale for the planet like the Holocene or the Pleistocene.Of the roughly 5 million to 9 million animal species living on Earth today, between 11,000 and 58,000 species likely go extinct every year, the Science study notes. Mass extinctions like today's, however, are rare.
Earth has experienced five previous mass extinction events, most caused by giant meteors slamming into the Earth. The best-known of these is probably the one that killed off the dinosaurs, along with 75 percent of all other species, about 66 million years ago. Ninety percent of all animal species were lost in another extinction more than 250 million years ago, which has been called the "Great Dying."What's different about today's extinction? "The underlying driving force for this is not a meteorite or a mega-volcanic eruption; it is one species - homo sapiens," Stanford University's Rodolfo Dirzo, one of the Science studies' lead authors, told USA Today.
The loss of a single species, while seemingly insignificant when compared to the overall number of animal species on Earth, leaves a much bigger hole in its ecosystem than humans know, the Science editors point out."Though for emotional or aesthetic reasons we may lament the loss of large charismatic species, such as tigers, rhinos, and pandas, we now know that loss of animals, from the largest elephant to the smallest beetle, will also fundamentally alter the form and function of the ecosystems upon which we all depend," the study says.
