Lions used to roam across most of Africa, southern Europe, and the Middle East, all the way to northwestern India. Today, there are fewer than 25,000 lions left in the wild, down from an estimated 400,000 in 1950. They cling to life in the confines of Sub-Saharan Africa, and the wilds of India's Gir forest. The vast majority of the lion population are gone - and their decline is thought to be but one part of a mass extinction event.

What is climate change? The definition, causes and effects Climate Change What is climate change? The definition, causes and effects

Between 1900 and 2015, nearly half of 177 surveyed mammal species lost more than 80 per cent of their distribution. Billions of populations of mammals, birds, reptiles and amphibians have been lost all over the planet, prompting scientists to suggest we have now entered a sixth mass extinction akin to a "biological annihilation".

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Professor Gerardo Ceballos, at the Universidad Nacional Autónoma de México, says that now, "the extinction of mammal populations, although varying from species to species, [is] a global phenomenon".

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His work, published in the journal Proceedings of the National Academy of Science, tracks the significant rate of mammalian extinction across the Earth - describing it as a “frightening assault on the foundations of human civilisation”.

In Earth's history, there have been five mass extinction events. The last, during the Cretaceous–Paleogene period, brought an end to the dinosaurs. A combination of volcanic activity and asteroid impacts resulted in the loss of 75 per cent of life on the planet, 65 million years ago. In the 21st Century, with anthropogenic changes to the climate and landscape of the world, a sixth extinction event could be on the horizon.

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Percentage of local population extinction in 177 species of mammals in 1° × 1° quadrats, as an indication of the severity of the mass extinction crises. The maps were generated by comparing historic and current geographic ranges. Gerardo Ceballos et. al

Large regions in all continents have lost 50 per cent or more of the populations of the evaluated mammals from 1900 to 2015. While the small sample size only covers 177 species, and is biased to larger mammals, this figure can be used to visualise likely trends in global population losses. Assuming that on average each of the 10,000km2 occupied quadrats studied held a single population of the species found within it, Ceballos estimates that roughly 58,000 populations of the 177 mammals examined have gone extinct.

Gerardo Ceballos et. al

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"Earth is now in a period of mass global species extinction for vertebrate animals," Ceballos says, "but the true extent of this mass extinction has been underestimated".

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This underestimation in the level of vertebrate extinction has been linked to the largely overlooked area of studying population shrinkage as opposed to solely species extinction. By focusing on this area, Ceballos doesn't wait until the species has disappeared, but tracks their current changes in population across the world - a method that outlines an overall trend of species decline.

Gerardo Ceballos et. al

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This method has limitations - namely the difficulty in ascertaining the actual average area occupied by a vertebrate population. But even using conservative estimates for smaller species, such as mammals, birds, reptiles, and amphibians, one population every 10km2 would result in hundreds of thousands of population extinctions over a few centuries. Moreover, population extinctions are preludes to larger species extinction.

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Regions exhibiting higher concentrations of species and population decline show a strong correspondence to an intertropical peak, roughly between the Tropics of Cancer and Capricorn. Areas of most devastating loss occur across the African continent, as well as India and Australia - but are prevalent around the globe.

Ceballos' study shows that creatures of all shapes and sizes, both vertebrates and invertebrates, are found to be in states of decline. In the UK, long-term monitoring of insect populations shows that 30 to 60 per cent of species have contracting ranges. The significance of this species loss cannot be understated.

Kenya Wildlife Services (KWS) rangers stand guard around illegal stockpiles of burning elephant tusks, ivory figurines and rhinoceros horns at the Nairobi National Park on April 30, 2016 TONY KARUMBA/AFP/Getty Images

Records covering 4,424 species, collected between 1970 and 2009 by the Centre for Ecology and Hydrology found losses across the UK. Of pollinators such as bees, moths and hoverflies, 28 per cent are in decline. Pest controllers such as ants have seen a 16 per cent loss.

Tom Oliver, an ecologist at the University of Reading who led this study, told the Guardian the consequences of losing wildlife would have stark repercussions on food production and our national ecosystem.

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“We need insects to pollinate our crops – we can’t do it by hand – and if we lose natural pest controls, less food will be available. If we lose those functions, the crops we eat won’t be able to be pollinated so the price of food would go hugely up and certain foods we wouldn’t be able to eat such as fruits including strawberries, raspberries and apples.”

Furthermore, slight changes in the ecosystem could drastically affect our ability to maintain arable land, with the diversity of tree and plant species also in decline.

The main threat to the Gibbon and Sarudung is homelessness which is pushing the species to the brink of extinction. Oil palm cultivation has cleared the vast forest area, removing the protected animal habitats in East Asia that the animals enjoyed. Albert Damanik / Barcroft Media / Barcroft Media via Getty Images

Ceballos' research is not alone in indicating an extinction level threat to biodiversity. 60 per cent of primate species - our closest biological relatives - are now threatened with extinction. Globally, 75 per cent have declining populations. Primates offer critical insights into human evolution, biology, and behaviour, yet it is the anthropogenic activity that is threatening their survival.

Forest loss resulting from regional and global economic pressures, the impacts of hunting, illegal trade, and other anthropogenic threats on global animal populations have led to sustained habitat loss and changes to many ecosystems, from Australia's coral reefs to the Amazonian rainforest.

The likelihood of Earth's extinction lies in the causes of population extinctions, Ceballo says. Rapid loss of animals across the globe and comparable losses in the diversity of plants, indicate a co-extinction of plants. Plants, vital sources of food, medicine and central absorbers of atmospheric CO2, are key to human life. Without them, an extinction level event for humans grows likely.

Ulet Ifansasti/Getty Images

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"Habitat conversion, climate disruption, overexploitation, toxification, species invasions, disease, and (potentially) large-scale nuclear war — all tied to one another in complex patterns and usually reinforcing each other’s impacts," Ceballo says. "Much less frequently mentioned are, however, the ultimate drivers of those immediate causes of biotic destruction, namely, human overpopulation and continued population growth, and over-consumption, especially by the rich."

At a glance, Ceballo's research presents a dark, but conservative insight into global biodiversity. It suggests that as much as 50 per cent of the number of animals that once shared Earth with us are already gone. Given the increasing trajectories of the drivers of extinction, the window for action to move towards a sustainable future is slowly closing.

"The sixth mass extinction is already here and the window for effective action is very short," Ceballo says, "probably two or three decades at most. All signs point to ever more powerful assaults on biodiversity in the next two decades, painting a dismal picture of the future of life, including human life."</s>The disappearance of entire species is not the only factor that contributes to mass extinction, it is also the reduction of populations within species, a new study argues, and calls the current rate of loss of terrestrial vertebrate populations a prelude to the sixth mass extinction.

The study by Gerardo Ceballos, from Universidad Nacional Autónoma de México in Mexico City, and Paul R. Ehrlich and Rodolfo Dirzo, from Stanford University, looked at about half of all known terrestrial vertebrate species — 27,600 birds, mammals, reptiles and amphibians. From within those, the researchers looked at detailed data of 177 mammals that have been well-studied between 1990 and 2015.

Read: 60% Of Primates, Closest Human Relatives, Could Be Extinct In 25 Years

“Using range reduction as a proxy for population loss, the study finds 32 percent of vertebrate species are declining in population size and range. Of the 177 mammals for which the researchers had detailed data, all have lost 30 percent or more of their geographic ranges and more than 40 percent have lost more than 80 percent of their ranges,” a statement on the Stanford site said.

“This is the case of a biological annihilation occurring globally, even if the species these populations belong to are still present somewhere on Earth,” Dirzo said in the statement.

Ehrlich had been part of another study in 2015 that “showed that Earth has entered an era of mass extinction unparalleled since the dinosaurs died out 66 million years ago.” Further, according to data maintained by the International Union for Conservation of Nature, about 41 percent of all amphibian species and 26 percent of all mammals were threatened by extinction, as of March 2016.

The new study, titled “Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines,” seems to substantiate those fears. Much of the blame is ascribed to anthropogenic causes which lead to large scale depletion of habitat for a number of the affected species. The areas worst affected are south and southeast Asia, where all the large mammals have lost over 80 percent of their geographical ranges.

“Anthropogenic population extinctions amount to a massive erosion of the greatest biological diversity in the history of Earth and that population losses and declines are especially important, because it is populations of organisms that primarily supply the ecosystem services so critical to humanity at local and regional levels,” the study says.

Read: First Mass Extinction 450 Million Years Ago Likely Caused By Volcano Eruption

The study’s lead author Ceballos said in the statement: “The massive loss of populations and species reflects our lack of empathy to all the wild species that have been our companions since our origins. It is a prelude to the disappearance of many more species and the decline of natural systems that make civilization possible.”

Giving examples of the importance of animals in any healthy ecosystem and even to humans, such as the pollination of crops by honeybees, Ehrlich said in the statement: “Sadly, our descendants will also have to do without the aesthetic pleasures and sources of imagination provided by our only known living counterparts in the universe.”

The authors cite human overpopulation and overconsumption in their study as the primary reasons driving the loss of individual members of various species, as well as the loss of species (two vertebrate species go extinct every year, on average), and call to undo “the fiction that perpetual growth can occur on a finite planet.” “We emphasize that the sixth mass extinction is already here and the window for effective action is very short, probably two or three decades at most. All signs point to ever more powerful assaults on biodiversity in the next two decades, painting a dismal picture of the future of life, including human life,” the authors conclude. The study appears in the journal Proceedings of the National Academy of Sciences.
• 5 Animals On The Brink Of Extinction Today</s>PARIS: The sixth mass extinction of life on Earth is unfolding more quickly than feared, and amounts to a "biological annihilation" of the planet's wildlife, scientists have warned.

More than 30 per cent of animals with a backbone - fish, birds, amphibians, reptiles and mammals - are declining in both range and population, according to the first global analysis of these trends.

"This is the case of a biological annihilation occurring globally," said Stanford professor Rodolfo Dirzo, co-author of a study published in the peer-reviewed journal PNAS.

Mammals have lost at least a third of their original habitat, the researchers found.

Forty per cent of those mammals - among them rhinos, orangutans, gorillas and many big cats - are surviving on 20 per cent or less of the land they once roamed.

The loss of biodiversity has recently accelerated, the study found.

"Several species of mammals that were relatively safe one or two decades ago are now endangered," including cheetahs, lions and giraffes, it said.

Globally, the mass die-off - the sixth in the last half-billion years - is the worst since three-quarters of life on Earth, including the non-avian dinosaurs, were wiped out 66 million years ago by a giant meteor impact.

On average, two vertebrate species disappear every year.

The study goes beyond extinction to map the dwindling ranges and populations of 27,600 species of animals, including 177 mammal types, between 1990 and 2015.

Tropical regions have seen the highest number of declining species. While fewer species are disappearing in temperate zones, the percentage is just as high or higher.

As much as half of the number of animals that once shared our planet are no longer here, a loss the authors described as "a massive erosion of the greatest biological diversity in the history of Earth."

There is no mystery as to why: our own ever-expanding species - which has more than doubled in number since 1960 to 7.4 billion - is eating, crowding and poisoning its planetary cohabitants out of existence.

The main drivers of wildlife decline are habitat loss, overconsumption, pollution, invasive species and disease.

Climate change is poised to become a major threat in the coming decades, with some animals - most famously polar bears - already in decline due to rising temperatures and changing weather patterns.</s>Earth has supported life for 3.5 billion years, but its hospitality is hardly consistent. Natural disasters have triggered at least five mass extinctions in the past 500 million years, each of which wiped out between 50 and 90 percent of all species on the planet. The most recent occurred about 65 million years ago, when an asteroid ended the reign of dinosaurs and opened new doors for mammals.

Now it's happening again. A 2015 study reported the long-suspected sixth mass extinction of Earth's wildlife is "already underway." And a new study calls the loss of that wildlife a “biological annihilation” and a “frightening assault on the foundations of human civilization.” Researchers from the Universidad Nacional Autónoma de México found that the rate of population loss is extremely high — even among species that are not considered endangered. They also found that up to half of all individual animals have been lost in the last few decades.

A 2016 study published in the journal Science also suggests this sixth mass extinction is killing off large ocean dwellers (like sharks, whales, giant clams, sea turtles and tuna) in disproportionately greater numbers than smaller animals. That's a reversal from past extinctions, when there was a slight connection between smaller size and going extinct.

And while previous extinctions were often linked to asteroids or volcanoes, this one is an inside job. It's caused mainly by one species — a mammal, ironically. The current crisis is the handiwork of humans, and we have a "unique propensity to cull the largest members of a population," the authors of the 2016 study write.

Many scientists have been warning us for years, citing a pace of extinctions far beyond the historical "background" rate. Yet critics have argued that's based on inadequate data, preserving doubt about the scope of modern wildlife declines. To see if such doubt is justified, the 2015 study compared a conservatively low estimate of current extinctions with an estimated background rate twice as high as those used in previous studies. Despite the extra caution, it still found species are disappearing up to 114 times more quickly than they normally do in between mass extinctions.

Here are six important things to know about life in the sixth mass extinction:

Once abundant in eastern North America, passenger pigeons were driven extinct by a surge of hunting and habitat loss. (Photo: Seabamirum/Flickr)

Extinction is a natural part of evolution, having already claimed an estimated 99 percent of all species in Earth's history. But things can get ugly when too many species die out too quickly, creating a domino effect capable of bringing down ecosystems. In the new study, researchers used a background rate of two mammal extinctions per 10,000 species per 100 years (2 E/MSY), which is double the background rate used in many previous studies. When they compared that to a conservative estimate of modern-day extinctions, they found no way to avoid calling this a mass extinction.

"Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 114 times higher than the background rate," the study's authors write. "Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way."

Deforestation is one of the primary threats for endangered species. (Photo: Fedorov Oleksiy/Shutterstock)

The No. 1 cause of modern wildlife declines is habitat loss and fragmentation, representing the primary threat for 85 percent of all species on the IUCN Red List. That includes deforestation for farming, logging and settlement, but also the less obvious threat of fragmentation by roads and other infrastructure.

And even where habitats aren't being razed or divided, they're increasingly altered by other human activities. Invasive species now threaten a variety of native plants and animals around the world, either by killing them directly or by outcompeting them for food and nest sites. Pollution is pervasive in many places, from chemicals like mercury that accumulate in fish to the plastic debris that slowly kills sea turtles, sea birds and cetaceans. Entire ecosystems are now migrating due to climate change, leaving behind less mobile or adaptable species. And in some parts of the world, poachers are obliterating rare species to meet demand for wildlife parts like rhino horn and elephant ivory.

The lemur tree frog is critically endangered and listed on the IUCN Red List. (Photo: G.J. Verspui/Shutterstock)

The number of vertebrate species that have definitely gone extinct since 1500 is at least 338, according to the new study. (That doesn't include the less stringent categories of "extinct in the wild" (EW) and "possibly extinct" (PE), which push the total up to 617.) More than half of those extinctions have occurred since 1900 — 198 in the "extinct" (EX) category, plus another 279 in EW and PE.

Even under the most conservative estimates, the extinction rates for mammals, birds, amphibians and fish have all been at least 20 times their expected rates since 1900, the researchers note (the rate for reptiles ranges from 8 to 24 times above expected). Earth's entire vertebrate population has reportedly fallen 52 percent in the last 45 years alone, and the threat of extinction still looms for many — including an estimated 41 percent of all amphibian species and 26 percent of mammals.

"There are examples of species all over the world that are essentially the walking dead," Ehrlich says.

4. It's probably still worse than we think.

Insecticides can weaken native pollinators like bees, raising concerns about food supplies. (Photo: Bjorn Watland/Flickr)

The new study is intentionally conservative, so the actual rate of extinctions is almost certainly more extreme than it suggests. "We emphasize that our calculations very likely underestimate the severity of the extinction crisis," the researchers write, "because our aim was to place a realistic lower bound on humanity's impact on biodiversity."

The study also focuses on vertebrates, which are typically easier to count than smaller or subtler wildlife like mollusks, insects and plants. As another recent study pointed out, this leaves much of the crisis unexamined. "Mammals and birds provide the most robust data, because the status of almost all has been assessed," write the authors of that study, published June 8 in the Proceedings of the National Academy of Sciences. "Invertebrates constitute over 99% of species diversity, but the status of only a tiny fraction has been assessed, thereby dramatically underestimating overall levels of extinction."

By incorporating data on terrestrial invertebrates, they add, "this study estimates that we may already have lost 7% of [contemporary] species on Earth and that the biodiversity crisis is real.

About 1 billion people rely on fish as their main source of animal protein, according to the World Health Organization. (Photo: Albert Pego/Shutterstock)

Humans are hardly an endangered species, with a global population of about 7.2 billion and growing. But fortunes can change quickly, as we've demonstrated in recent decades with lots of other wildlife. And despite our best efforts to buffer ourselves against the whims of nature, civilization remains reliant on healthy ecosystems for food, water and other resources. Adjusting to mass extinctions would be a challenge under any circumstances, but it's especially daunting in the context of climate change.

"If it is allowed to continue, life would take many millions of years to recover, and our species itself would likely disappear early on," says Gerardo Ceballos of the Universidad Autónoma de México, lead author of the new study. "We are sawing off the limb that we are sitting on," Ehrlich adds.

6. Unlike an asteroid, we can be reasoned with.

An artist's rendering of the asteroid widely credited with wiping out the dinosaurs. (Photo: NASA)

Previous mass extinctions may have been inevitable, but it's not too late to stop this one. While the authors of the new study acknowledge the difficulty of curbing lucrative destruction like deforestation, not to mention climate change, they note it is still possible. It's even gaining momentum, thanks to growing public awareness as well as high-profile attention from governments, corporations and even the pope.

"Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species," the study's authors write, "and to alleviate pressures on their populations — notably habitat loss, over-exploitation for economic gain and climate change."

That won't be easy, but at least it's more of a chance than the dinosaurs got.

Editor's note: This story has been updated since it was originally published in June 2015.</s>New Delhi: Scientists have warned that the Earth, our home planet, is undergoing sixth mass extinction and is more severe than previously thought.

Calling the loss of wildlife a "biological annihilation" that represents a "frightening assault on the foundations of human civilisation", they say billions of regional or local populations have been lost.

Scientists held human overpopulation and overconsumption responsible for the massive loss of wildlife.

Previous studies have shown species are going extinct at a significantly faster rate than for millions of years before, but even so extinctions remain relatively rare giving the impression of a gradual loss of biodiversity.

The new work instead takes a broader view, assessing many common species which are losing populations all over the world as their ranges shrink, but remain present elsewhere.

The scientists found that a third of the thousands of species losing populations are not currently considered endangered and that up to 50 per cent of all individual animals have been lost in recent decades.

Almost half of land mammals have lost 80 per cent of their range in the last century, 'The Guardian' reported.

The scientists found billions of populations of mammals, birds, reptiles and amphibians have been lost all over the planet, leading them to say a sixth mass extinction has already progressed further than was thought.

"The resulting biological annihilation obviously will have serious ecological, economic and social consequences," researchers said.

"Humanity will eventually pay a very high price for the decimation of the only assemblage of life that we know of in the universe," they said.

In the study, researchers analysed the population trends of 27,500 land vertebrate species, including a detailed analysis of 177 species of mammals, and found that the ranges of a third have shrunk in recent decades.

The study has been published in the journal Proceedings of the National Academy of Sciences.</s>Sixth mass extinction already under way

A “biological annihilation” of wildlife in recent decades means a sixth mass extinction in Earth’s history is under way and is more severe than previously feared, according to research.

Scientists analysed both common and rare species and found billions of regional or local populations have been lost. They blame human overpopulation and overconsumption for the crisis and warn that it threatens the survival of human civilisation, with just a short window of time in which to act.

The study, published in the peer-reviewed journal Proceedings of the National Academy of Sciences, eschews the normally sober tone of scientific papers and calls the massive loss of wildlife a “biological annihilation” that represents a “frightening assault on the foundations of human civilisation”.

Prof Gerardo Ceballos, at the Universidad Nacional Autónoma de México, who led the work, said: “The situation has become so bad it would not be ethical not to use strong language.”

Previous studies have shown species are becoming extinct at a significantly faster rate than for millions of years before, but even so extinctions remain relatively rare giving the impression of a gradual loss of biodiversity. The new work instead takes a broader view, assessing many common species which are losing populations all over the world as their ranges shrink, but remain present elsewhere.

The scientists found that a third of the thousands of species losing populations are not currently considered endangered and that up to 50% of all individual animals have been lost in recent decades. Detailed data is available for land mammals, and almost half of these have lost 80% of their range in the last century. The scientists found billions of populations of mammals, birds, reptiles and amphibians have been lost all over the planet, leading them to say a sixth mass extinction has already progressed further than was thought.

The scientists conclude: “The resulting biological annihilation obviously will have serious ecological, economic and social consequences. Humanity will eventually pay a very high price for the decimation of the only assemblage of life that we know of in the universe.”

They say, while action to halt the decline remains possible, the prospects do not look good: “All signs point to ever more powerful assaults on biodiversity in the next two decades, painting a dismal picture of the future of life, including human life.”

Wildlife is dying out due to habitat destruction, overhunting, toxic pollution, invasion by alien species and climate change. But the ultimate cause of all of these factors is “human overpopulation and continued population growth, and overconsumption, especially by the rich”, say the scientists, who include Prof Paul Ehrlich, at Stanford University in the US, whose 1968 book The Population Bomb is a seminal, if controversial, work.

“The serious warning in our paper needs to be heeded because civilisation depends utterly on the plants, animals, and microorganisms of Earth that supply it with essential ecosystem services ranging from crop pollination and protection to supplying food from the sea and maintaining a livable climate,” Ehrlich told the Guardian. Other ecosystem services include clean air and water.

“The time to act is very short,” he said. “It will, sadly, take a long time to humanely begin the population shrinkage required if civilisation is to long survive, but much could be done on the consumption front and with ‘band aids’ – wildlife reserves, diversity protection laws – in the meantime.” Ceballos said an international institution was needed to fund global wildlife conservation.

The research analysed data on 27,500 species of land vertebrates from the IUCN and found the ranges of a third have shrunk in recent decades. Many of these are common species and Ceballos gave an example from close to home: “We used to have swallows nesting every year in my home near Mexico city – but for the last 10 years there are none.”

The researchers also point to the “emblematic” case of the lion: “The lion was historically distributed over most of Africa, southern Europe, and the Middle East, all the way to northwestern India. [Now] the vast majority of lion populations are gone.”

Prof Stuart Pimm, at Duke University in the US and not involved in the new work, said the overall conclusion is correct, but he disagrees that a sixth mass extinction is already under way: “It is something that hasn’t happened yet – we are on the edge of it.”

Pimm also said there were important caveats that result from the broad-brush approach used. “Should we be concerned about the loss of species across large areas – absolutely – but this is a fairly crude way of showing that,” he said. “There are parts of the world where there are massive losses, but equally there are parts of the world where there is remarkable progress. It is pretty harsh on countries like South Africa which is doing a good job of protecting lions.”

Robin Freeman, at the Zoological Society of London, UK, said: “While looking at things on aggregate is interesting, the real interesting nitty gritty comes in the details. What are the drivers that cause the declines in particular areas?”

Freeman was part of the team that produced a 2014 analysis of 3000 species that indicated that 50% of individual animals have been lost since 1970, which tallies with the new work but was based on different IUCN data. He agreed strong language is needed: “We need people to be aware of the catastrophic declines we are seeing. I do think there is a place for that within the [new] paper, although it’s a fine line to draw.”

Citing human overpopulation as the root cause of environmental problems has long been controversial, and Ehrlich’s 1968 statement that hundreds of millions of people would die of starvation in the 1970s did not come to pass, partly due to new high-yielding crops that Ehrlich himself had noted as possible.

Ehrlich has acknowledged “flaws” in The Population Bomb but said it had been successful in its central aim – alerting people to global environmental issues and the the role of human population in them. His message remains blunt today: “Show me a scientist who claims there is no population problem and I’ll show you an idiot.”

A severe ice age led to sea level falling by 100m, wiping out 60-70% of all species which were prominently ocean dwellers at the time. Then soon after the ice melted leaving the oceans starved of oxygen.

A messy prolonged climate change event, again hitting life in shallow seas very hard, killing 70% of species including almost all corals.

The big one – more than 95% of species perished, including trilobites and giant insects – strongly linked to massive volcanic eruptions in Siberia that caused a savage episode of global warming.

Three-quarters of species were lost, again most likely due to another huge outburst of volcanism. It left the Earth clear for dinosaurs to flourish.

An giant asteroid impact on Mexico, just after large volcanic eruptions in what is now India, saw the end of the dinosaurs and ammonites. Mammals, and eventually humans, took advantage.</s>Two vertebrate species go extinct every year on average, but few people notice, perhaps because the rate seems relatively slow - not a clear and present threat to the natural systems we depend on. This view overlooks trends of extreme decline in animal populations, which tell a more dire story with cascading consequences, according to a new study that provides the first global evaluation of these population trends.

"This is the case of a biological annihilation occurring globally, even if the species these populations belong to are still present somewhere on Earth," said co-author Rodolfo Dirzo, a professor of biology.

A 2015 study co-authored by Paul Ehrlich, professor emeritus of biology, and colleagues showed that Earth has entered an era of mass extinction unparalleled since the dinosaurs died out 66 million years ago. The specter of extinction hangs over about 41 percent of all amphibian species and 26 percent of all mammals, according to the International Union for Conservation of Nature (IUCN), which maintains a list of threatened and extinct species. This global disaster scene has the fingerprints of habitat loss, overexploitation, invasive organisms, pollution, toxification and climate change.

The new analysis, published in Proceedings of the National Academy of Sciences, looks beyond species extinctions to provide a clear picture of dwindling populations and ranges. The researchers mapped the ranges of 27,600 species of birds, amphibians, mammals and reptiles - a sample representing nearly half of known terrestrial vertebrate species - and analyzed population losses in a sample of 177 well-studied mammal species between 1990 and 2015.

Using range reduction as a proxy for population loss, the study finds more than 30 percent of vertebrate species are declining in population size and range. Of the 177 mammals for which the researchers had detailed data, all have lost 30 percent or more of their geographic ranges and more than 40 percent have lost more than 80 percent of their ranges. Tropical regions have had the greatest number of decreasing species while temperate regions have seen similar or higher proportions of decreasing species. Particularly hard hit have been the mammals of south and southeast Asia, where all the large-bodied species of mammals analyzed have lost more than 80 percent of their geographic ranges.

The study's maps suggest that as much as 50 percent of the number of animal individuals that once shared Earth have disappeared, as have billions of animal populations. This amounts to "a massive erosion of the greatest biological diversity in the history of Earth," the authors write.

"The massive loss of populations and species reflects our lack of empathy to all the wild species that have been our companions since our origins," said the new study's lead author, Gerardo Ceballos of the National Autonomous University of Mexico. "It is a prelude to the disappearance of many more species and the decline of natural systems that make civilization possible."

Why does the loss of populations and biological diversity matter? Aside from being what the scientists call a prelude to species extinction, the losses rob us of crucial ecosystem services such as honeybees' crop pollination, pest control and wetlands' water purification. We also lose intricate ecological networks involving animals, plants and microorganisms - leading to less resilient ecosystems and pools of genetic information that may prove vital to species' survival in a rapidly changing global environment.

"Sadly, our descendants will also have to do without the aesthetic pleasures and sources of imagination provided by our only known living counterparts in the universe," said Ehrlich.

In the meantime, the overall scope of population losses makes clear the world cannot wait to address biodiversity damage, according to the authors. They call for curbs on the basic drivers of extinction - human overpopulation and overconsumption - and challenge society to move away from "the fiction that perpetual growth can occur on a finite planet."

Dirzo is also the Bing Professor in Environmental Science. Dirzo and Ehrlich are senior fellows at the Stanford Woods Institute for the Environment.

More information: Gerardo Ceballos el al., "Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines," PNAS (2017). www.pnas.org/cgi/doi/10.1073/pnas.1704949114</s>Our planet is experiencing its sixth mass extinction event, and it is much more severe than previously thought, scientists have shown. The decline of many populations of vertebrate species is so dramatic that they call this a biological annihilation.

The loss of biodiversity on Earth is a pressing problem. Over the last century, 200 species of vertebrates have gone extinct – about two species per year.

This however, does not tend to generate a lot of public concern, mainly because many species that have recently disappeared were 'obscure species' with a limited range.

Take for example the Christmas Island pipistrelle, a small bat which went extinct in 2009 – few people even knew of its existence.

Studying these extinctions is important, as these losses are irreversible and can have a profound effect on the whole ecosystem. However, focusing on specific species can lead people to ignore the bigger picture, and to think that Earth's biodiversity is only slowly entering a major extinction episode.

The new study published in PNAS argues that looking at declines in species' populations – groups of organisms belonging to the same species in a given locality - conveys a much better idea of the threats faced by the planet's biodiversity.

The scientists analysed data from the International Union for Conservation of Nature (IUCN) to map the ranges of 27,600 birds, amphibians, mammals, and reptiles worldwide at a 10,000 km2 scale. This represents nearly half of known terrestrial vertebrate species.

They also conducted more detailed geographic analysis documenting population extinctions between 1900 and 2015, in 177 mammal species.

The researchers found that within many different species, the rate of population loss is very high. This is even the case for some species classified by the IUCN as of 'low concern'. In fact, the scientists estimate that about a third of all the species they studied have decreasing populations.

The geographic analyses revealed that between 1900 and 2015, all species had lost at least 30% of their geographic ranges and that more than 40% of the species had experienced more than 80% range reduction.

Hence, the data suggests that beyond global species extinction, our planet is experiencing a huge episode of vertebrate population declines, with a devastating impact on the environment. This can indeed have profound effects ranging from the depletion of Earth's resources to the deterioration of ecosystem function and services.

"Population extinctions are a prelude to species extinctions, so Earth's sixth mass extinction episode has proceeded further than most assume," the researchers write. "We describe this as a 'biological annihilation' to highlight the current magnitude of Earth's ongoing sixth major extinction event."

The causes of these population declines are varied, ranging from habitat loss and over-exploitation to pollution and climate change.

Human overpopulation and ongoing population growth coupled with over-consumption, may also be a problem.

One thing is certain though - robust measures must be taken very urgently to protect vulnerable vertebrate populations.

"We emphasise that the sixth mass extinction is already here and the window for effective action is very short, probably two or three decades at most," the scientists conclude.</s>When plant and animal species go extinct, it's usually a clear sign that humans have messed up. We've over-hunted, destroyed habitats, polluted waterways, and altered the climate by burning fossil fuels, wiping species off the planet for good.

We tend to study extinctions to understand just how much we have disrupted the planet's ecosystems. But in a new scientific study published on Monday, scientists said we're not paying nearly enough attention to the "prelude" to global extinction — as in, the dwindling population sizes and ranges of existing species that can be a warning sign of a bigger extinction event to come.

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As with extinctions, these declines have serious consequences for the natural systems we all depend on for clean air and water, food, and shelter.

"This is the case of a biological annihilation occurring globally, even if the species these populations belong to are still present somewhere on Earth," Rodolfo Dirzo, the study's co-author and a biology professor at the Stanford Woods Institute for the Environment, said in a press release.

For their analysis, published in the Proceedings of the National Academy of Sciences, Dirzo and his colleagues mapped the ranges of 27,600 species of birds, amphibians, mammals, and reptiles worldwide. The sample represents nearly half of all known land-based vertebrate species.

Scientists estimated that, of these species, nearly one-third of the vertebrates are declining in population size and range. Shrinking ranges mean animals — especially migratory species — have less room to hunt, breed, and hunker down.

As ranges decline, population numbers also dwindle, pushing a species closer to the edge of extinction.

Tropical regions saw the greatest number of decreasing species, particularly in south and southeast Asia. In Thailand and Myanmar, for instance, illegal hunting and logging of rosewood trees has drastically reduced the population of Indochinese tigers. Indonesia's Sumatran orangutan has lost roughly 60 percent of its habitat as farmers burn and drain swamp forests to produce palm oil.

Temperate regions had similar or higher proportions of decreasing species compared to tropical regions, according to the study.

Dirzo and his co-authors also looked at 177 well-analyzed mammal species and examined population losses between 1990 and 2015. Within this group, all have lost 30 percent or more of their geographic ranges. Some had been hit especially hard: more than 40 percent of the species have lost over 80 percent of their ranges. "It is a prelude to the disappearance of many more species and the decline of natural systems that make civilization possible," Gerardo Ceballos, the study's lead author and an ecology professor at the National Autonomous University of Mexico, said in the press release. Monday's research adds to the broader scientific debate about the " " — which is likely happening to the planet right now, and might be the biggest mass extinction since the dinosaurs disappeared 66 million years ago. During Earth's 4.5-billion-year history, five major extinction events have wiped out nearly all the species on the planet, the geological record shows. Asteroid strikes, volcanic eruptions, and natural climate shifts were likely to blame for those past events. However, this sixth mass die-off is largely due to human activities, such as population growth, habitat destruction, pollution, and climate change. In their paper, Dirzo, Ceballos, and Stanford professor Paul Ehrlich suggested that billions of animal populations that once roamed the Earth are gone. A separate 2016 study by World Wildlife Fund said global populations of vertebrates have declined by 58 percent between 1970 and 2012. The authors of Monday's paper said their research shows "Earth's sixth mass extinction has proceeded further than most assume." They added that the steep population declines amount to a "massive erosion of the greatest biological diversity" in Earth's history.
Between 1900 and 2015, around 177 species of mammals have lost 80% of their distribution leading to a presumption that the Holocene extinction is accelerating.