Earth’s sixth mass extinction has begun, new study confirms

James Dyke, University of Southampton

We are currently witnessing the start of a mass extinction event the likes of which have not been seen on Earth for at least 65 million years. This is the alarming finding of a new study published in the journal Science Advances.

The research was designed to determine how human actions over the past 500 years have affected the extinction rates of vertebrates: mammals, fish, birds, reptiles and amphibians. It found a clear signal of elevated species loss which has markedly accelerated over the past couple of hundred years, such that life on Earth is embarking on its sixth greatest extinction event in its 3.5 billion year history.

This latest research was conducted by an international team lead by Gerardo Ceballos of the National Autonomous University of Mexico. Measuring extinction rates is notoriously hard. Recently I reported on some of the fiendishly clever ways such rates have been estimated. These studies are producing profoundly worrying results.

However, there is always the risk that such work overestimates modern extinction rates because they need to make a number of assumptions given the very limited data available. Ceballos and his team wanted to put a floor on these numbers, to establish extinction rates for species that were very conservative, with the understanding that whatever the rate of species lost has actually been, it could not be any lower.

This makes their findings even more significant because even with such conservative estimates they find extinction rates are much, much higher than the background rate of extinction – the rate of species loss in the absence of any human impacts.

Here again, they err on the side of caution. A number of studies have attempted to estimate the background rate of extinction. These have produced upper values of about one out of every million species being lost each year. Using recent work by co-author Anthony Barnosky, they effectively double this background rate and so assume that two out of every million species will disappear through natural causes each year. This should mean that differences between the background and human driven extinction rates will be smaller. But they find that the magnitude of more recent extinctions is so great as to effectively swamp any natural processes.

Cumulative vertebrate species recorded as extinct or extinct in the wild by the IUCN (2012). Dashed black line represents background rate. This is the ‘highly conservative estimate’.
Ceballos et al

The “very conservative estimate” of species loss uses International Union of Conservation of Nature data. This contains documented examples of species becoming extinct. They use the same data source to produce the “conservative estimate” which includes known extinct species and those species believed to be extinct or extinct in the wild.

The paper has been published in an open access journal and I would recommend reading it and the accompanying Supplementary Materials. This includes the list of vertebrate species known to have disappeared since the year 1500. The Latin names for these species would be familiar only to specialists, but even the common names are exotic and strange: the Cuban coney, red-bellied gracile, broad-faced potoroo and southern gastric brooding frog.

Farewell, broad-faced potoroo, we hardly knew ye.
John Gould

These particular outer branches of the great tree of life now stop. Some of their remains will be preserved, either as fossils in layers of rocks or glass eyed exhibits in museum cabinets. But the Earth will no longer see them scurry or soar, hear them croak or chirp.

You may wonder to what extent does this matter? Why should we worry if the natural process of extinction is amplified by humans and our expanding industrialised civilisation?

One response to this question essentially points out what the natural world does for us. Whether it’s pollinating our crops, purifying our water, providing fish to eat or fibres to weave, we are dependent on biodiveristy. Ecosystems can only continue to provide things for us if they continue to function in approximately the same way.

The relationship between species diversity and ecosystem function is very complex and not well understood. There may be gradual and reversible decreases in function with decreased biodiversity. There may be effectively no change until a tipping point occurs. The analogy here is popping out rivets from a plane’s wing. The aircraft will fly unimpaired if a few rivets are removed here or there, but to continue to remove rivets is to move the system closer to catastrophic failure.

This latest research tells us what we already knew. Humans have in the space of a few centuries swung a wrecking ball through the Earth’s biosphere. Liquidating biodiversity to produce products and services has an end point. Science is starting to sketch out what that end point could look like but it cannot tell us why to stop before we reach it.

If we regard the Earth as nothing more than a source of resources and a sink for our pollution, if we value other species only in terms of what they can provide to us, then we we will continue to unpick the fabric of life. Remove further rivets from spaceship earth. This not only increases the risk that it will cease to function in the ways that we and future generations will depend on, but can only reduce the complexity and beauty of our home in the cosmos.

The Conversation

James Dyke is Lecturer in Complex Systems Simulation at University of Southampton.

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Whips hurt horses – if my leg’s anything to go by

Paul McGreevy, University of Sydney

It’s not just the horses that wear blinkers during the Melbourne Cup, the so-called “race that stops a nation”, which takes place next Tuesday. Perhaps it’s the excitement, the champagne or the extraordinary speed of the race, but most Melbourne Cup Day punters appear blithely unaware that they are actually watching horses being whipped … and hard.

Last year more than 100,000 people attended the Melbourne Cup, with more than 3 million watching the race on TV in Australia alone. This would have to make whipping in horse-racing the most public form of violence to animals in Australia today, but most people don’t seem to notice it.

Some 75% of whip strikes hit the horse’s flank (side of the abdomen), in contravention of the International Agreement on Breeding, Racing and Wagering.
Liss Ralston

To be fair, it was only when I saw high-speed images of whip impact that showed visible indentation of the skin in 83% of impacts I appreciated how likely it was that routine whipping of horses in racing causes pain. As a veterinarian, riding instructor and horse behaviourist, I am ashamed to admit how late this revelation came to me.

That I had to see it to believe it made me consider the extraordinary impact of images in achieving positive change for animals over the centuries, and what modern-day imagery might achieve.

William Hogarth most graphically illustrates the whipping of tired horses in his 1751 engraving The Four Stages of Cruelty: Second Stage of Cruelty (pictured below).

In his Autobiographical Notes Hogarth says the images:

were done in the hopes of preventing in some degree that cruel treatment of poor Animals which makes the streets of London more disagreeable to the human mind …

William Hogarth’s Second Stage of Cruelty in which Tom Nero whips his horse in public.
Wikimedia Commons

Hogarth’s First Stage of Cruelty shows youths already comfortable in their abuse of animals such as dogs, cats and birds. As his series progresses, it becomes apparent society as a whole is either indifferent to or encourages cruelty, and that this augurs very badly.

Hogarth’s images nail the nexus between animal cruelty and human crime and violence, and are as relevant today as they were 263 years ago. Images of horses being whipped on the streets of Victorian England are recognised as a major impetus to the birth of the animal protection movement as we know it today.

These were exhausted work and carriage horses and observers could see they were being thrashed to deliver more effort, where none was possible.

Today horses are still whipped in public, but only in the name of sport. And while there are restrictions on the number of times the whip can be used during a race, the Sport of Kings removes these safeguards in the last 100m, when the horses are tired and unlikely to be able to give any more. As if this isn’t futile enough, there is no peer-reviewed evidence that shows using the whip at any time increases performance.

Indeed, in 2011, my laboratory used cutting-edge imaging technologies to demonstrate the futility of whipping, and was awarded a Eureka Voiceless Prize for this work.

The racing industry assures us that every whip used in racing must be padded and that “when used properly, the whip stimulates a horse and should not cause pain”. However, my analysis of high-speed videography shows that the padding fails to protect horses in 64% of strikes. It also shows that 70% of whip strikes are delivered “backhand”, so are not counted under rules limiting the number of strikes.

While there are plenty of international agreements on whip use, they seem to achieve little. One ruling embraced by more than 40 countries, including Australia, is that horses should not be struck on the flank (the side of the abdomen). When we studied more than 100 strikes with frame-by-frame analysis, we discovered that more than 75% were flank strikes. And yet, to my knowledge, no Australian jockey has ever been penalised for flouting this rule.

Liss Ralston

The use of animals in research in Australia, including to investigate whether whipping a horse hurts, requires compliance with rules adopted under animal welfare legislation. These include the proviso:

Pain and distress may be difficult to evaluate in animals. Unless there is evidence to the contrary, it must be assumed that procedures and conditions that would cause pain and distress in humans cause pain and distress in animals.

Given there is no evidence to show that whipping horses doesn’t hurt, I decided to find out whether having my leg struck with a racing whip, as hard as jockeys whip horses, would cause me pain and distress.

Well, the answer is a resounding “yes”, and the thermographic images I took clearly show heat at the site of impact. In the image below you can see white areas of inflammation in my upper leg 30 minutes after it was struck – only once. And a warning: this material is disturbing.

My view is that – because there is no evidence to the contrary – we must assume that, just as I felt pain and distress from the impact of the padded whip, similar whipping in a horse would also cause pain and distress.

Representatives from the racing industry will doubtless say horses have thick skin and are therefore immune to pain from whip impacts but there is actually no evidence of such pain resistance in horses. Indeed, horses can feel a fly on their skin such that it triggers a characteristic shake called the “panniculus reflex”.

As sports journalist Patrick Smith recently wrote:

if whips didn’t cause pain there would be no use to them.

Unfortunately, the Australian Racing Board has recently advised me that “it will not be participating” in a non-invasive study I proposed using the thermographic camera on horses before and after races to investigate exactly what changes whipping causes to horseflesh.

As a veterinarian and scientist, I believe that when such thermographic images become available, they will remove the public’s blinkers to reveal the unnecessary cruelty caused by whipping in horse racing, just as Hogarth’s engravings did for work and carriage horses.

Since 1888, the winning jockey at the Melbourne Cup has been presented with a golden whip. At the very least, isn’t it time to stop glorifying an instrument of, at best, discomfort and, at worst, pain? You bet it is.

The Conversation is currently running a series looking at the history and nature of violence.

Paul McGreevy is Professor of Animal Behaviour and Animal Welfare Science at University of Sydney.

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Wolf cull backfires as wild canines feast on farm animals

Niki Rust, University of Kent

Wolves, lions and other large carnivores rely on meat for sustenance and there are only so many wild animals to go round. Sometimes, dinner means cow or sheep.

Farmers can use guard dogs or protective fencing to deter predators and protect livestock. But lethal methods such as hunting and trapping are also used to control wild carnivore numbers.

As a livestock farmer in wolf country, it would be reasonable to assume that killing more predators would result in fewer attacks on your animals. However, a new study by Washington State University has turned this assumption on its head by discovering the opposite: the more wolves that are killed (up to a threshold of 25% of the population), the more the remainder preyed on local sheep and cows. Why is this?

Unpicking the pack

The researchers, Robert Wielgus and Kaylie Peebles, point to the nature of the species’ social systems: wolves live in family groups containing a breeding pair (also known as the alpha pair) along with related sub-adults, juveniles and pups. The alphas are the only breeders within the group as they limit reproduction by their subordinates.

Killing one of the alphas disrupts the pack and subordinate wolves, who often outnumber the breeders, are then free to reproduce. This could increase the number of breeding individuals in the area, thereby increasing the population of hungry wolves – maybe farmers who shoot wolves are inadvertently doing more towards conservation than they think!

Wolves take on a Bison.

Conversely, as humans are more likely to shoot youngsters than adult breeding wolves, the alphas may be temporarily be in a more favourable situation. There would be less competition for food, fewer clashes with other wolves and less risk of the transmission of disease. Again, this could result in short-term increases in attacks on livestock.

Wolf packs also have an important educational role, as the experienced wolves pass on their knowledge. Killing them impairs this social learning. If the rest of the pack hasn’t learnt the skills necessary to take on bison or elk they may instead turn towards easier pickings on the farm.

This same behaviour has been seen in lions and cougars (although has not been documented in many other carnivore species).

When culls go wrong

It is interesting to note that this paradoxical finding is not just found in relation to wolves – lethal control of cougars (or mountain lions) also means the remainder kill more cows and sheep as younger, inexperienced cougars are more likely to attack livestock.

Coyote vs sheep.

Coyotes also show increased litter sizes and more frequent breeding in populations that were lethally controlled. Culling programmes could have even exacerbated livestock attacks by taking out younger, less predatory coyotes. Further, state-funded coyote removal campaigns have failed to reduce predation on sheep. Lynx, too, do not significantly reduce livestock attacks until lethal control dramatically reduces total population numbers.

It must be noted that other studies have shown that killing predators can sometimes reduce the numbers of livestock they themselves kill, but this is only temporary, until new populations of predators establish themselves.

What to do about wolves?

If we would like a world where neither livestock nor predators are killed, we are either going to have to take away all the predators or all the livestock. Clearly neither one of these options is viable so we must aim to reduce preying on farm animals to a tolerable level.

Should’ve ordered the lamb.
Denali NPS

Despite proof that changes in livestock husbandry reduces predation, farmers may still not want these creatures living near them as they may feel that the carnivores have “won” or taken over “their” land.

As such, despite scientific evidence showing that predators don’t kill that many cattle anyway, that lethal control usually doesn’t reduce attacks, and that non-lethal methods can almost eliminate attacks, this still may not be enough to sway farmers from their anti-predator mind-sets.

We must therefore start to think outside the box. Much of this conflict between humans and wild predators is not really about protecting livestock, but instead concerns a deeper historic and cultural aversion to wolves, lions and other scary carnivores. This won’t be fixed through simple technical solutions – and we now know it certainly won’t be fixed with a gun.

The Conversation

Niki Rust is PhD candidate in Carnivore Conservation at University of Kent.

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Rewilding isn’t about nostalgia – exciting new worlds are possible

Paul Jepson, University of Oxford

The restoration of natural ecosystems – “rewilding” – ought to be a chance to create inspiring new habitats. However the movement around it risks becoming trapped by its own reverence of the past; an overly nostalgic position that makes rewilding less realistic and harder to achieve.

The recent launch of Rewilding Britain is certainly exciting and timely. However George Monbiot’s vision of bringing back 15 iconic species falls short of the rewilding visions being discussed in universities.

These are emerging from advances in functional ecology and Earth system science. The vision of rewilding is more ambitious: it is about restoring ecological processes through reassembling the species that drive them. For example rooting by wild boars has repercussions throughout a woodland ecosystem. Such animals shouldn’t be reintroduced simply because they were once there, but because they could do something productive in future.

Don’t go native

Monbiot’s quest to restore “lost” species harks back to a past age. However many conservation scientists are more relaxed concerning the question of “nativenes”. They are willing to consider introducing non-native species if they contribute a functional role in ecosystems, and they view the past not as a benchmark to preserve or replicate but as an inspiration for ecosystem restoration.

For instance, “Monbiot’s 15” omits the auroch and tarpan which are classed as extinct. However in the 1980s progressive Dutch ecologists realised that their functional analogues survived as cattle and ponies and their ecological role could be restored through “de-domestication”.

They set about de-domesticating them at the famous Oostvaardersplassen reserve located a 40 minute drive from Amsterdam. This produced a “Serengeti-like” landscape: a type of nature unknown to Europe since humans settled down and started farming.

The auroch (or ‘heck cattle’) is king of the OVP.
Jan Nijendijk, CC BY-SA

The OVP, as it is known, made nature conservation political again and has become a landmark public experiment in ecology. I first visited it with a group of students in 2003 when we travelled to the Netherlands to meet the radical ecologist Frans Vera and engage with the controversies created by rewilding.

The OVP is created on reclaimed land and opponents argued that the fences and flood control created an artifical landscape that undermined any claims to its authenticity as a restored ecosystem. More seriously the policy of allowing the cattle and ponies to die of “natural” starvation enraged animal welfare and farmer groups who believed they should be subjected to the same welfare standards applied to animals in labs, farms and zoos.

The controversies surrounding the experiment, Vera’s hypothesis that Europe’s original vegetation was wood-pasture rather than high-forest, and other radical rewilding visions are inspiring a re-examination of the fundamental premise of nature conservation.

Rewilding’s big chance

I recently published a Rewilding agenda for Europe in the journal Ecography, as my contribution to the European Council’s “fitness check” of its nature legislation. The Birds and Habitats directives under review derive from the science and policy context of the 1970s. They are ageing. Both science and society have moved on.

Any revisions to European nature legislation should support the creation of experimental rewilding sites. Across the UK we could imagine the creation of wild cattle and pony step-lands on the Ridgeway, wild boar and deer-driven woodland ecosystems in Wales, and a Scottish arcadia of bison, moose, wolves and pine forest.

Wild boars in Wales?
vlod007, CC BY

We also need many more OVP-like public rewilding experiments close to urban areas. These would be contained sites that inspire and inform the public about scientific advances, and provoke us all to ask: what sort of nature do we want for the future?

Rewilding might offer fresh solutions to intractable conservation problems. For example, conservationists want to remove pine trees introduced to the Sefton Coast dune system near Liverpool but local residents love them for their scenic grandeur and red squirrels. The famous Formby footprints dating from 2,500 BC show that humans, wild cattle, deer and wolf once inhabited these coastal areas. Suggesting the reintroducing of wild cattle and companion herbivores and seeing what happens might prompt a unified vision for the dunes.

In practice rewilding is constrained by regulations on biohazards, public access and animal husbandry – and rigid and powerful 20th century conservation legislation and agencies which have no real incentive to innovate.

Conservation institutions need to modernise but no one wants to dismantle them and start over. We need designated spaces with regulatory flexibility – experimental rewilding sites – where we can plan future natures that will improve the quality of life for people and the planet.

Ordinary people are disenfranchised. Conservation policy is influenced by a coordinated lobby of a few big charities who have built their organisational models on the institutional structures of the late 20th century. George Monbiot’s vision catches the attention but advocates of rewilding need to develop realistic policy mechanisms to take their ideas forward. Rewilding experiments would give space for wider reflection and debate and give our conservation institutions time to adapt. Crucially they would reinvigorate conservation as a cultural force in the 21st century.

The Conversation

Paul Jepson is Course Director, MSc Biodiversity, Conservation and Management at University of Oxford.

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DNA evidence proves climate change killed off prehistoric megafauna

Chris Turney, UNSW Australia and Alan Cooper

Imagine a world populated by woolly mammoths, giant sloths and car-sized armadillos – 50,000 years ago more than 150 types of these mysterious large-bodied mammals roamed our planet. But by 10,000 years ago, two-thirds of them had disappeared.

Since the end of the 19th century, scientists have puzzled over where these “megafauna” went. In 1796, the famous French palaeontologist Georges Cuvier suggested a global catastrophe had wiped them out. Others were appalled. The great Thomas Jefferson was so against Cuvier’s idea he sent an expedition to try to find vast herds of these animals grazing contentedly in the American interior. The only thing anyone could say with certainty was there should be a lot more of them than we see today.

Alfred Wallace, who wrote the first paper on evolution by natural selection with Charles Darwin, noted that “we live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared”. It’s one of the great historical whodunnits: what happened to the megafauna, and when did they disappear?

The two-tonne glyptodon survived until 10,000 years ago.
Pavel Riha, CC BY-SA

As with any good mystery, there are two main suspects: climate and humans.

The idea that our ancestors may have hunted the huge beasts to extinction has long been a popular view, particularly as the spread of humans around the world appears closely associated with their demise. Several major criticisms continue to be levelled at this theory, the most popular being that many large animals are still present in Africa, despite it having the longest record of occupation by people. Others in turn argue that humans co-evolved alongside megafauna in Africa for millions of years, giving animals time to learn from human behaviour.

The alternative is that a rapidly changing climate caused the habitat of the megafauna to shrink or disappear. As the planet warmed out of the last ice age 12,000 years ago, many animals would have struggled to adapt to the new environment. A major criticism here is that there have been other major climatic changes in the past, some of which have been equally extreme and rapid. What could have been so different with this most recent warming?

In a research paper published in the journal Science, we report new advances in ancient DNA, carbon dating and climate reconstruction that finally give some answers. Previously, as long as species appeared to survive in the fossil record the interpretation had been that nothing significant had happened for tens of millennia.

But thanks to ancient DNA analysis of megafaunal bones we now know that this approach has missed a series of events throughout the past 50,000 years when major parts of a species’ genetic diversity, or even the whole species itself, disappeared. Alongside this, more accurate carbon dating of the fossil remains shows these extinctions did not all happen at a single time but were staggered through time and space.

The authors recently discovered this DNA-filled mammoth vertebrae preserved in ice, while doing fieldwork in northern Canada.
Kieren Mitchell, Author provided

It’s important to realise the backdrop to these extinctions was a wildly fluctuating climate. The ice age of the northern hemisphere was not one long frigid wasteland. Instead, frozen conditions were punctuated by many short, rapid warming periods, known as interstadials, where temperatures would soar from 4 to 16˚C within just a few decades and last for hundreds to thousands of years. They represent some of the most profound climate changes detected in the recent geological past.

When we precisely compared the dates for European and American extinctions with climate records, we were amazed to find they coincided with the abrupt warming of the interstadials; in stark contrast there is a complete absence of extinctions at the height of the last ice age. As temperatures rose during the interstadials, dramatic shifts in global rainfall and vegetation patterns would have placed the megafauna under immense stress. Those that could not adapt to the rapidly changing conditions would have quickly succumbed. The European cave lion, for instance (Panthera leo spelaea in the chart below), survived through periods when much of the continent was covered in ice, only to go extinct during relatively benign conditions around 14,500 years ago.

Megafaunal extinctions mapped against climate change. Temperature history is shown along the bottom; the black and red bars represent 95% confidence ranges. Most animals went extinct during warm interstadial periods (shaded brown), and the last ice age (shaded blue) had almost no effect.
Cooper et al

There seems little doubt humans would have contributed to extinctions, however. While the dramatic climate shifts were the major driver in megafaunal extinction events, humans would have applied the coup de grâce to populations already suffering major stress.

In one likely scenario, humans would have concentrated their hunting efforts along dispersal routes, killing the few bold individuals moving out to re-establish an extinct population, causing localised extinctions to expand into larger and larger areas, that would have eventually led to an irreversible ecosystem collapse. It’s likely the scattered pattern of extinctions and the difficulty of detecting them from fossils alone is why the relationship with warming events has not been detected before.

So what does this mean for the future? Well for a start, rapidly increasing temperatures are not good news for the megafauna that survived the last warming. In many ways the rise of atmospheric CO2 levels and resulting warming effects are expected to have a similar rate of change to the onset of past interstadials, heralding another major phase of large mammal extinctions.

This seems all the more likely thanks to our “success” in developing the planet’s surface, breaking up areas of natural habitat and disrupting any connectivity that once existed between areas. Migration is becoming increasingly less of an option for species struggling to adapt to changing temperatures with little chance of back filling from neighbouring areas for re-establishing populations. Even after all these years, megafauna are providing a precious lesson from the past.

The Conversation

Chris Turney is Professor and ARC Laureate Fellow at UNSW Australia.
Alan Cooper is Director, Australian Centre for Ancient DNA at University of Adelaide.

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