sixth mass extinction event

Earth has entered into a sixth mass extinction event

Animal populations across the planet have decreased by as much as 80 per cent since 1900 - an event akin to "biological annihilation". The consequences for humans could be severe

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.


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".
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".

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.

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.
"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".

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.

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.

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.

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.

“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.

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

"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."





http://www.wired.co.uk/article/sixth-mass-extinction-humans-animals-conservation

http://www.pnas.org/content/early/2017/07/05/1704949114