What killed off the giant beasts, climate change or man?

By Robin McKie for The Guardian,

Earth’s ‘megafauna’ vanished as tribes spread. Now palaeontologists are asking if early humans were the cause

Humans might have played a role in the extinction of the woolly mammoth. Photograph: Andrew Nelmerm/Getty Images/Dorling Kindersley

They were some of the strangest animals to walk the Earth: wombats as big as hippos, sloths larger than bears, four-tusked elephants, and an armadillo that would have dwarfed a VW Beetle. They flourished for millions of years, then vanished from our planet just as humans emerged from their African homeland.

It is one of palaeontology’s most intriguing mysteries and formed the core of a conference at Oxford University las 20th of march when delegates debated whether climate change or human hunters killed off the planet’s lost megafauna, as these extinct giants are known.

“Creatures like megatherium, the giant sloth, and the glyptodon, a car-sized species of armadillo, disappeared in North and South America about 10,000 years ago, when there were major changes to climates – which some scientists believe triggered their extinctions,” said Yadvinder Malhi, professor of ecosystem science at Oxford, one of the organisers of the conference, Megafauna and Ecosystem Function.

“However, it is also the case that tribes of modern humans were moving into these creatures’ territories at these times – and many of us believe it is too much of a coincidence that this happened just as these animals vanished. These creatures had endured millions of years of climate change before then, after all. However, this was the first time they had encountered humans.”

Modern humans emerged from Africa around 70,000 years ago, travelled across Asia and reached Australia 50,000 years ago, a time that coincides with a wave of extinctions of creatures there, including the diprotodon, a species of wombat that grew to the size of a modern hippopotamus. By about 14,000 years ago, humans had reached North America by crossing the land bridge that then linked Siberia and Alaska. Then they headed south.

By 10,000 years ago, Homo sapiens had conquered North and South America at a time that coincided with major megafauna extinctions, including those of the giant sloth and the glyptodon.

“We think of Africa and south-east Asia – with their lions, elephants and rhinos – as the main home of large animals today, but until very recently in our planet’s history, huge creatures thrived in Australia, North America and South America as well,” said Professor Adrian Lister of the Natural History Museum in London. “The question is: why did they disappear in the new world but survive in the old world?

“Some believe it is because large animals in Africa and south-east Asia learned to become wary of human beings and decided to avoid them at all costs. However, I also think climate change may have been involved in the Americas and Australia and that humans only finished off these big animals when they were already weakened by loss of habitats and other climate-related problems.”

The idea that humans were involved in any way in eradicating dozens of species of giant animal when we were still hunter-gatherers has important implications in any case. It was thought, until relatively recently, that it was only when humans invented agriculture several thousand years ago that our species’ relationship with the natural world become unbalanced. Until then, humans had a close affinity with nature. But if ancient hunter-gatherers played a part in wiping out these species of huge animals as long as 50,000 years ago, humanity’s supposed innate harmony with the living world appears misplaced.

More to the point, humanity is still paying the price for the disappearance of the megafauna of the Americas and Australia, the Oxford conference will hear. “There is now a lot of evidence to suggest that large herbivores like gomphotheres, a family of elephant-like animals that went extinct in South America around 9,000 years, played a key role in spreading nutrition in areas like the Amazon. They would eat fruit in the forest, including avocados, and their excrement would then fertilise other areas. That no longer happens and places like the Amazon are today affected by low nutrition as a result,” Malhi said.

Another example is provided by the giant wombat, the diprotodon, which some scientists have argued browsed bush across Australia and kept biomass levels very low. When the diprotodon vanished, plants and shrubs across the outback grew unhindered. The result was major bush fires which, archaeologists have discovered, became a serious problem just after the giant wombat disappeared from Australia.

Drastic population fluctuations explain the rapid extinction of the passenger pigeon

The number of passenger pigeons went from billions to zero in mere decades, in contrast to conventional wisdom that enormous population size provides a buffer against extinction. Our understanding of the passenger pigeon’s extinction, however, has been limited by a lack of knowledge of its long-term population history. Here we use both genomic and ecological analyses to show that the passenger pigeon was not always super abundant, but experienced dramatic population fluctuations, which could increase its vulnerability to human exploitation. Our study demonstrates that high-throughput–based ancient DNA analyses combined with ecological niche modeling can provide evidence allowing us to assess factors that led to the surprisingly rapid demise of the passenger pigeon.

To assess the role of human disturbances in species’ extinction requires an understanding of the species population history before human impact. The passenger pigeon was once the most abundant bird in the world, with a population size estimated at 3–5 billion in the 1800s; its abrupt extinction in 1914 raises the question of how such an abundant bird could have been driven to extinction in mere decades. Although human exploitation is often blamed, the role of natural population dynamics in the passenger pigeon’s extinction remains unexplored. Applying high-throughput sequencing technologies to obtain sequences from most of the genome, we calculated that the passenger pigeon’s effective population size throughout the last million years was persistently about 1/10,000 of the 1800’s estimated number of individuals, a ratio 1,000-times lower than typically found. This result suggests that the passenger pigeon was not always super abundant but experienced dramatic population fluctuations, resembling those of an “outbreak” species. Ecological niche models supported inference of drastic changes in the extent of its breeding range over the last glacial–interglacial cycle. An estimate of acorn-based carrying capacity during the past 21,000 y showed great year-to-year variations. Based on our results, we hypothesize that ecological conditions that dramatically reduced population size under natural conditions could have interacted with human exploitation in causing the passenger pigeon’s rapid demise. Our study illustrates that even species as abundant as the passenger pigeon can be vulnerable to human threats if they are subject to dramatic population fluctuations, and provides a new perspective on the greatest human-caused extinction in recorded history.

This article contains supporting information online at http://www.pnas.org/content/suppl/2014/06/13/1401526111.DCSupplemental/pnas.1401526111.sapp.pdf

Reference:

Chih-Ming Hung, Pei-Jen L. Shaner,Robert M. Zink, Wei-Chung Liu,Te-Chin Chu, Wen-San Huang, Shou-Hsien Li

Drastic population fluctuations explain the rapid extinction of the passenger pigeon PNAS 2014 ; published ahead of printJune 16, 2014,

http://www.pnas.org/content/early/2014/06/11/1401526111?

Long lives, big impacts: human life expectancy linked to extinctions

by Dominic Rowland 

Since the arrival of Homo sapiens, other species have been going extinct at an unprecedented rate. Most scientists now agree that extinction rates are between 100 and 1000 times greater than before humans existed. Working out what is driving these extinctions is fiendishly complicated, but a new study by scientists from the University of California, Davis and the Nebraska Cooperative Fish and Wildlife Research Unit suggests that human life expectancy may be partly to blame. 

“Increased life expectancy means that people live longer and affect the planet longer; each year is another year of carbon footprint, ecological footprint, use of natural resources, etc.,“ the authors write. “The magnitude of this impact is increased as more people live longer.” 

The study used a computer model to examine human impacts on birds and mammals. By comparing the number of invasive and endangered species between countries, the researchers examined the effects of many human variables such as gross domestic product (GDP), pesticide use, tourism, agriculture, wilderness protection, global trade, regulation and life expectancy. 


The Stephens Island Wren (Xenicus [Traversia] lyalli) was a flightless, nocturnal bird limited to one small island off the coast of New Zealand. It was driven to extinction by cats in the late 1800s. 

“It’s not a random pattern,” said lead author Aaron Lotz, a postdoctoral scholar in the Department of Wildlife, Fish and Conservation at UC Davis. “Out of all this data, that one factor — human life expectancy — was the determining factor for endangered and invasive birds and mammals.” 

The study also looked at the effects of wealth, with GDP per capita strongly linked to increased numbers of both invasive and endangered bird and mammal species. 

“Humanity’s global influence is orders of magnitude greater than that of any other species, primarily because of the large human population size, anthropogenic CO2 production, biomass consumption, energy use and geographical range size,” the writers state in their paper. 

When comparing countries, New Zealand came off as the worst with a dramatic decline in biodiversity since human colonization. This is partially because its absence of native land mammals has meant that native fauna has evolved in insolation from many types of predators. Once introduced by human colonists, these invasive animals ravaged the country, driving many native species to extinction. African countries, by contrast, had the fewest invasive species, partially explained because lower levels of international trade introduced fewer exotic stowaways 

“Even though the analysis in this study does not determine mechanisms, the patterns observed in this study clearly suggest that there is a relationship between humans (i.e., living longer and thus having a longer negative impact on the planet) and the loss of endangered species,” Lotz said. 

“We must continue to make direct links between people and nature and give people incentives, tools, and the capacity to manage ecosystems sustainably. Some studies have this view that there’s wildlife and then there’s us. But we’re part of the ecosystem. We need to start relating humans to the environment in our research and not leave them out of the equation. We need to realize we have a direct link to nature.” 


Average human life expectancies of countries around the world. Courtesy of Creative Commons Attribution-Share Alike 3.0.Click to enlarge. 

Citations:

• Lotz A, Allen CR. Social-Ecological Predictors of Global Invasions and Extinctions. Ecol Soc. (2013)18(3).

Source: http://news.mongabay.com/2014/0415-rowland-life-expectancy.html

Dingos May Have Outfoxed Tigers

New evidence suggests that thylacines were driven to extinction on the mainland by dingo attacks rather than competition for food, as previously thought.

Thylacines flourished widely until around 3500 years ago. Their disappearance from areas other than Tasmania co­incided with the arrival of the dingo, which never reached Tasmania.

It is common for predators to kill smaller species that might represent competition. However, this was once dismissed as a possible explanation for the thylacine’s mainland disappearance since the Tasmanian tiger was larger than dingos.

Dr Mike Letnic of the University of NSW says this view ignores Bergmann’s Rule – the observation that animals are larger in colder climates – so Letnic and colleagues at the University of Sydney compared the size of thylacine and dingo bones from similar areas. They found a substantial overlap in size, but some adult thylacines were much smaller than any dingoes.

Evidence from Tasmania shows that thylacines were highly sexually dimorphic, with the females much smaller than the males. Although it is not possible to identify the sex of most of the fossils, it seems likely that male thylacines were of similar size to dingoes while females were not much larger than foxes.

“Recent studies have shown that foxes are suppressed in areas that have many dingoes, and it appears that the dingoes kill the foxes. Hence we believe that the same mechanism occurred 3500–5000 years ago with dingoes killing thylacines,” says Dr Mathew Crowther of Sydney University’s School of Biological Sciences.

Male thylacines may have been large enough to fight off dingos, but the females would probably have succumbed, leaving the species unable to breed.

In PloS One the researchers argued that direct attacks by dingoes may have wiped out the thylacines. “Recent analysis has found the evidence for competition as a driver of extinction is weak,” Letnic says. “It can have a big effect on abundance, but usually a species can find a location in which it can survive. Direct killing is harder to avoid, particularly with an introduced species, which the smaller animal may lack adaptations to avoid.”

Letnic acknowledges that the theory lacks direct evidence, such as dingo bite marks on thylacine fossils. However, he says finding this would be “like looking for a needle in a haystack”.

The paper also raises the possibility that changes in Aboriginal culture and economy, coinciding with the dingo’s arrival, may have contributed, as might the dingo’s greater tendency to hunt in packs.

Source: http://www.australasianscience.com.au/article/issue-julyaugust-2012/dingos-may-have-outfoxed-tigers.html

Paper conclusion:
Dingoes were similarly sized to male thylacines but were considerably larger than female thylacines on mainland Australia during the Holocene. Small size may have made female thylacines particularly susceptible to direct killing by dingoes and such killing could have driven thylacines to extinction. Due to their lower metabolic rate and convergent morphology, thylacines would have also been susceptible to resource competition with dingoes, but competition is generally thought to be a weaker extinction threat than predation. Our results provide support for the hypothesis that direct killing by larger dingoes contributed to the extinction of the thylacine on mainland Australia. However, attributing the extinction of the thylacine to just one cause is problematic because the arrival of dingoes coincided with another potential extinction driver, the intensification of the human economy.

Access to the paper: http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pone.0034877&representation=PDF

Humans have always been the nemesis of the planet’s wildlife

By George Monbiot, published in the Guardian 25th March 2014

A dead elephant in the Hwange National Park, Zimbabwe, thought to have died after poachers poisoned a salt lick with cyanide. Photograph: Aaron Ufumeli/EPA

You want to know who we are? Really? You think you do, but you will regret it. This article, if you have any love for the world, will inject you with a venom – a soul-scraping sadness – without an obvious antidote.

The Anthropocene, now a popular term among scientists, is the epoch in which we live: one dominated by human impacts on the living world. Most date it from the beginning of the industrial revolution. But it might have begun much earlier, with a killing spree that commenced two million years ago. What rose onto its hindlegs on the African savannahs was, from the outset, death: the destroyer of worlds.

Before Homo erectus, perhaps our first recognisably-human ancestor, emerged in Africa, the continent abounded with monsters. There were several species of elephants. There were sabretooths and false sabretooths, giant hyaenas and creatures like those released in The Hunger Games: amphicyonids, or bear dogs, vast predators with an enormous bite.

Professor Blaire van Valkenburgh has developed a means by which we could roughly determine how many of these animals there were(1). When there are few predators and plenty of prey, the predators eat only the best parts of the carcass. When competition is intense, they eat everything, including the bones. The more bones a carnivore eats, the more likely its teeth are to be worn or broken. The breakages in carnivores’ teeth were massively greater in the pre-human era(2).

Not only were there more species of predators, including species much larger than any found on earth today, but they appear to have been much more abundant – and desperate. We evolved in a terrible, wonderful world – that was no match for us.

Homo erectus possessed several traits that appear to have made it invincible: intelligence, cooperation; an ability to switch to almost any food when times were tough; and a throwing arm that allowed it to do something no other species has ever managed – to fight from a distance. (The increasing distance from which we fight is both a benchmark and a determinant of human history). It could have driven giant predators off their prey and harried monstrous herbivores to exhaustion and death.

Artist’s rendition of a prehistoric mastodon. Photograph: Bettmann/Corbis

As the paleontologists Lars Werdelin and Margaret Lewis show, the disappearance of much of the African megafauna appears to have coincided with the switch towards meat eating by human ancestors(3). The great extent and strange pattern of extinction (concentrated among huge, specialist animals at the top of the food chain) is not easy to explain by other means.

At the Oxford megafauna conference last week, I listened as many of the world’s leading scientists in this field mapped out a new understanding of the human impact on the planet(4). Almost everywhere we went, humankind erased a world of wonders, changing the way the biosphere functions. For example, modern humans arrived in Europe and Australia at about the same time – between 40 and 50,000 years ago – with similar consequences. In Europe, where animals had learnt to fear previous versions of the bipedal ape, the extinctions happened slowly. Within some 10 or 15,000 years, the continent had lost its straight-tusked elephants, forest rhinos, hippos, hyaenas and monstrous scimitar cats.

In Australia, where no hominim had set foot before modern humans arrived, the collapse was  almost instant. The rhinoceros-sized wombat(5), the ten-foot kangaroo, the marsupial lion, the monitor lizard larger than a Nile crocodile(6), the giant marsupial tapir, the horned tortoise as big as a car(7) – all went, in ecological terms, overnight.

A few months ago, a well-publicised paper claimed that the great beasts of the Americas – mammoths and mastodons, giant ground sloths, lions and sabretooths, eight-foot beavers(8), a bird with a 26-foot wingspan(9) – could not have been exterminated by humans, because the fossil evidence for their extinction marginally pre-dates the evidence for human arrival(10).

Artist’s rendition of a pack of dire wolves and two mammoths. Photograph: Stocktrek Images/Alamy

I have never seen a paper demolished as elegantly and decisively as this was at last week’s conference. The archaeologist Todd Surovell demonstrated that the mismatch is just what you would expect if humans were responsible(11). Mass destruction is easy to detect in the fossil record: in one layer bones are everywhere, in the next they are nowhere. But people living at low densities with basic technologies leave almost no traces. With the human growth rates and kill rates you’d expect in the first pulse of settlement (about 14,000 years ago), the great beasts would have lasted only 1,000 years. His work suggests that the most reliable indicator of human arrival in the fossil record is a wave of large mammal extinctions.

These species were not just ornaments of the natural world. The new work presented at the conference suggests that they shaped the rest of the ecosystem. In Britain during the last interglacial period, elephants, rhinos and other great beasts maintained a mosaic of habitats: a mixture of closed canopy forest, open forest, glade and sward(12). In Australia, the sudden flush of vegetation that followed the loss of large herbivores caused stacks of leaf litter to build up, which became the rainforests’ pyre: fires (natural or manmade) soon transformed these lush places into dry forest and scrub(13).

In the Amazon and other regions, large herbivores moved nutrients from rich soils to poor ones, radically altering plant growth(14,15). One controversial paper suggests that the eradication of the monsters of the Americas caused such a sharp loss of atmospheric methane (generated in their guts) that it could have triggered the short ice age which began 12,800 years ago, called the Younger Dryas(16).

And still we have not stopped. Poaching has reduced the population of African forest elephants by 65% since 2002(17). The range of the Asian elephant – which once lived from Turkey to the coast of China – has contracted by 97%; the ranges of the Asian rhinos by over 99%(18). Elephants distribute the seeds of hundreds of rainforest tree species; without them these trees are functionally extinct(19,20).

Is this all we are? A diminutive monster that can leave no door closed, no hiding place intact, that is now doing to the great beasts of the sea what we did so long ago to the great beasts of the land? Or can we stop? Can we use our ingenuity, which for two million years has turned so inventively to destruction, to defy our evolutionary history?

http://www.monbiot.com

References:

1. eg Wendy J. Binder and Blaire Van Valkenburgh, 2010. A comparison of tooth wear and breakage in Rancho La Brea sabertooth cats and dire wolves across time. Journal of Vertebrate Paleontology. http://www.tandfonline.com/doi/abs/10.1080/02724630903413016#.UzBUcM40uQk

2. http://www.eci.ox.ac.uk/news/events/2014/megafauna/valkenburgh.pdf

3. Lars Werdelin, 2013. King of Beasts. Scientific American. http://www.scientificamerican.com/magazine/sa/2013/11-01/

4. http://oxfordmegafauna.weebly.com/

5. Diprotodon.

6. Megalania.

7. http://www.wired.com/wiredscience/2010/08/last-giant-land-turtle/

8. Castoroides ohioensis

9. The Argentine roc (Argentavis magnificens).

10. Matthew T. Boulanger and R. Lee Lyman, 2014. Northeastern North American Pleistocene megafauna chronologically overlapped minimally with Paleoindians. Quaternary Science Reviews 85, pp35-46. http://dx.doi.org/10.1016/j.quascirev.2013.11.024

11. http://www.eci.ox.ac.uk/news/events/2014/megafauna/surovell.pdf

12. Christopher J. Sandom et al, 2014. High herbivore density associated with vegetation diversity in interglacial ecosystems. Proceedings of the National Academy of Sciences, vol. 111, no. 11, pp4162–4167. http://www.pnas.org/cgi/doi/10.1073/pnas.1311014111

13. Susan Rule et al, 23rd March 2012. The Aftermath of Megafaunal Extinction: Ecosystem Transformation in Pleistocene Australia. Science Vol. 335, pp 1483-1486. doi: 10.1126/science.1214261. https://www.sciencemag.org/content/335/6075/1483.full

14. Christopher E. Doughty, AdamWolf and Yadvinder Malhi, 11 August 2013. The legacy of the Pleistocene megafauna extinctions on nutrient availability in Amazonia. Nature Geoscience vol. 6, pp761–764. doi: 10.1038/ngeo1895. http://www.nature.com/ngeo/journal/v6/n9/full/ngeo1895.html

15. Adam Wolf, Christopher E. Doughty, Yadvinder Malhi, Lateral Diffusion of Nutrients by Mammalian Herbivores in Terrestrial Ecosystems. PLOS One, doi: 10.1371/journal.pone.0071352. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0071352

16. Felisa A. Smith, 2010. Methane emissions from extinct megafauna. Nature Geoscience 3, 374 – 375. doi:10.1038/ngeo877. http://www.nature.com/ngeo/journal/v3/n6/full/ngeo877.html

17. Fiona Maisels, pers comm. This is an update of the figures published here: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0059469

18. http://www.eci.ox.ac.uk/news/events/2014/megafauna/campos.pdf

19. http://www.eci.ox.ac.uk/news/events/2014/megafauna/campos.pdf

20. http://www.eci.ox.ac.uk/news/events/2014/megafauna/galetti.pdf

Sources: http://www.monbiot.com/2014/03/24/destroyer-of-worlds/

http://www.theguardian.com/commentisfree/2014/mar/24/humans-diminutive-monster-destruction?

How long have humans been transforming the planet?

A call goes out for a new global effort to puzzle out humanity’s ecological history over the last 50,000 years or more By David Biello

Want to know when the Anthropocenestarted exactly? It will only cost an entirely revamped scientific effort in archaeology, ecology and paleontology, among other disciplines, at an unprecedented planetary scale, according to a new paper calling for such a scheme.

The putative start date for what scientists have begun to call the Anthropocene—a newly defined epoch in which humanity is the dominant force on the planet—ranges widely. Some argue that humans began changing the global environment about 50,000 years back, in the Pleistocene epoch, helping along if not outright causing the mass extinctions of megafauna, from mammoths to giant kangaroos, on most continents. Others date it to the emergence of agriculture some 7,000 years ago. The most definitive cases to be made coincide with the start of the industrial revolution and the dawn of the atomic age. The beginnings of burning fossil fuels to power machines in the 19th century initiated a change in the mix of atmospheric gases , and the first nuclear weapon test on July 16, 1945, spread unique isotopes across the globe.

There is little doubt from the archaeological record that humans have been altering ecosystems on a local scale for at least 50,000 years if not longer, but the extent of that alteration remains unknown. Recent work by ecologist Erle Ellis of the University of Maryland, Baltimore County, and others suggests that for at least 3,000 years hunting, farming and burning have shaped most landscapes on the planet, based on computer models.

To definitively prove that with field evidence would require the kind of archaeological and ecological effort the world has never seen, a scheme Ellis and co-authors lay out in a paper in the inaugural issue of the new open-access journal Elementa, devoted to the Anthropocene. That plan, they say, would have to be global in scale—to eliminate the bias in current research toward the most accessible archaeological sites—as well as unusually open. Few scientific disciplines are as secretive as archaeology, paleontology and paleoecology, given that careers are made (or not) based on access to specimens.

The payoff would be a true historical baseline for what is “natural” for the first time, complementing efforts like the Long Term Ecological Research Network and the newNational Ecological Observatory Network, among others. “What is a natural system has a cultural history as part of its constitution,” says archaeologist Dorian Fuller of University College London, a co-author of the paper and a supporter of “Big Archaeology,” who notes that the ecosystems of Amazonia, Europe and even the western U.S. are all products of at least millennia of human activity.

Prospects for such a global effort are, admittedly, dim, not least because it is unclear who would fund such work. But a global, synthetic effort is the only way to answer the question: How long have humans been terraforming? “This is great scientific work that can be done and needs to be done,” Ellis argues. “It will help us define the role of humans in shaping the Anthropocene and will mark a scientific triumph for humanity: a full empirical account of our rise to global stewardship of the biosphere.”

Source: http://www.scientificamerican.com/article.cfm?id=length-of-human-domination&WT.mc_id=SA_CAT_EVO_20131209

Collapse of the Sahara’s megafauna

By Dr. Sarah Durant, Zoological Society of London, Wildlife Conservation Society, and National Geographic’s Big Cats Initiative

There are few landscapes more evocative and beautiful than the sweeping sands and majestic mountains of the Sahara desert. This land used to be widely populated by large animals uniquely adapted to the harsh and unpredictable desert environment. Their ability to roam freely across a vast landscape following sparse rainfall and forage is key to their survival in an unforgiving habitat.

However, over recent times, there has been a catastrophic decline in wildlife in the Sahara. In a new article  that documents the status of large animal species in the region, we show that, out of 14 species historically found in the Sahara, most have been eradicated from 90% or more of their historical range.

Species such as the Addax used to roam widely across the Sahara, but now number only a couple of hundred individuals – the recently established Termit and Tin-Toumma National Nature Reserve in Niger is one of their last strongholds. Photograph by Thomas Rabeil/Sahara Conservation Fund.

Several species have disappeared entirely. The last known photograph of the iconic Scimitar horned oryx was taken in 1982 by John Newby (photo below), and the species was declared extinct in the wild in 1999 (it only survives now in captivity).

This photo, taken by John Newby from the Sahara Conservation Fund in 1982, is thought to be the last of scimitar-hornedoryx in the wild. Photograph by John Newby/Sahara Conservation Fund.

Less information survives on the precise time of disappearance of another three species that have been eradicated from the region: the lion; bubal hartebeest;  and the African wild dog. Critically endangered addax, dama gazelle and Saharan cheetah cling on in tiny fragmented populations, while endangered populations of slender-horned and Cuvier’s gazelles are not faring much better.

You might think that such a catastrophic collapse of an entire megafauna would be making headlines, and that something would be done to stop it, but it has gone ahead largely unnoticed and unreported.

Deserts have become almost invisible on the conservation agenda. World attention has, understandably, focused on the rich biodiversity found in hotspots, which are often in tropical forests. However, deserts actually harbour surprisingly high levels of biodiversity, able to thrive in a harsh and highly variable environment.  This biodiversity hides a wealth of adaptations that enable species to tolerate water stress and extreme temperatures; information that may prove critical as we are forced to adapt to a changing climate.

Unsustainable hunting and past and ongoing insecurity have undoubtedly played a key role in the loss of Saharan wildlife, but it is difficult to avoid the conclusion that more attention might have helped prevent some of the declines. Rare antelope and Saharan cheetah can still be found in remote and inaccessible corners of the Sahara, in vast landscapes possessing a silent peace and unforgettable beauty.

There are also some good news stories—Niger has just established a massive 97,000km2reserve—Termit and Tin Toumma National Nature Reserve, which harbours most of the world’s 200 or so remaining wild addax and one of a handful of surviving populations of dama gazelle and Saharan cheetah. While there is hope that we may yet see scimitar horned oryx back in the wild in the Ouadi Rimé-Ouadi Achim Game Reserve, with the support of the Chadian government.

2014 is the halfway point in the United Nations Decade for Deserts and the Fight against Desertification and the fourth year of the United Nations Decade for Biodiversity. It is an opportune time for the world to focus on securing the sustainable management of desert ecosystems, to the benefit of people and wildlife. The world will be a poorer place if the unique biodiversity of the Sahara and other deserts is allowed to disappear.

Saharan landscapes, such as found in the Ahaggar Cultural Park photographed here, are stunningly beautiful. Photograph by Sarah Durant/Zoological Society of London.

Source: http://newswatch.nationalgeographic.com/2013/12/03/117914/

Access to the scientific paper:

http://onlinelibrary.wiley.com/doi/10.1111/ddi.12157/abstract

More about it:

http://www.scienceworldreport.com/articles/11354/20131204/catastrophic-decline-in-sahara-s-wildlife-population-study-cautions.htm

 

Climate change, not human activity, led to megafauna extinction

Most species of gigantic animals that once roamed Australia had disappeared by the time people arrived, a major review of the available evidence has concluded.

The research challenges the claim that humans were primarily responsible for the demise of the megafauna in a proposed “extinction window” between 40,000 and 50,000 years ago, and points the finger instead at climate change.

An international team led by the University of New South Wales, and including researchers at the University of Queensland, the University of New England, and the University of Washington, carried out the study. It is published in the Proceedings of the National Academy of Sciences.

“The interpretation that humans drove the extinction rests on assumptions that increasingly have been shown to be incorrect.  Humans may have played some role in the loss of those species that were still surviving when people arrived about 45,000 to 50,000 years ago – but this also needs to be demonstrated,” said Associate Professor Stephen Wroe, from UNSW, the lead author of the study.

“There has never been any direct evidence of humans preying on extinct megafauna in Sahul, or even of a tool-kit that was appropriate for big-game hunting,” he said.

About 90 giant animal species once inhabited the continent of Sahul, which included mainland Australia, New Guinea and Tasmania.

“These leviathans included the largest marsupial that ever lived – the rhinoceros-sized Diprotodon – and short-faced kangaroos so big we can’t even be sure they could hop. Preying on them were goannas the size of large saltwater crocodiles with toxic saliva and bizarre but deadly marsupial lions with flick-blades on their thumbs and bolt cutters for teeth,” said Associate Professor Wroe.

The review concludes there is only firm evidence for about 8 to 14 megafauna species still existing when Aboriginal people arrived. About 50 species, for example, are absent from the fossil record of the past 130,000 years.

Recent studies of Antarctic ice cores, ancient lake levels in central Australia, and other environmental indicators also suggest Sahul – which was at times characterised by a vast desert – experienced an increasingly arid and erratic climate during the past 450,000 years.

Arguments that humans were to blame have also focused on the traditional Aboriginal practice of burning the landscape. But recent research suggests that the fire history of the continent was more closely linked to climate than human activity, and increases in burning occurred long before people arrived.

“It is now increasingly clear that the disappearance of the megafauna of Sahul took place over tens, if not hundreds, of millennia under the influence of inexorable, albeit erratic, climatic deterioration,” said Associate Professor Wroe.

Media Contacts: Deborah Smith,  UNSW Science +612 9385 7307, + 61 478 492 060,

 

Cheetahs on the brink

Over the course of several thousand years, the cheetah served as an important status symbol in numerous civilizations including the Egyptian, Persian, Mughal, and Frankish Empires. Akbar the Great was said to have kept 1,000 cheetahs on his palace grounds, and Emperor Haile Selassie of Ethiopia had an affinity for keeping them as pets.

But like many large African and Asiatic mammals, cheetahs are now threatened by a loss of habitat, genetic issues, poaching, and a range of other problems. The fastest land animal on earth is now threatened by extinction and is in a race against time as its numbers dwindle, with just over a few thousands remaining in the wild.

Photographer Frans Lanting and filmmaker Christine Eckstrom have spent years documenting the natural world and teaching people how they can coexist with wildlife. In the following film from National Geographic Live, Lanting and Eckstrom explain how they documented rare cheetahs in Africa and in Iran and what challenges lay ahead for these elusive felines.

Global cheetah populations have plummeted over the past century, from an estimated 100,000 cheetahs in 1900 to fewer than 10,000 today. And once upon a time, cheetahs roamed the deserts of Iran. But international scientificsurveys recently confirmed what Iranian biologists already suspected– today there are fewer than 100 Asiatic cheetahs left on earth.

The Iranian Cheetah Society, founded in 2001, has started using social media, including their youtube channel, to promote awareness about endangered Asiatic cheetahs in Iran. The organization posts short video clips from their research in northeastern Iran, both in the Miandasht Wildlife Refuge and the Behkadeh Reserve, featuring rare Iranian cheetahs in the wild.

The dwindling population of Persian gazelles, devastated by heavy poaching in previous decades, has negatively impacted Iran’s cheetahs. Poachers are a serious threat to many endangered species across the Middle East.

A recent picture we featured of Lebanese bird hunters and their kill in a national park sparked fiery debates on social media. And in the case of Iran, both their cheetah and leopard populations are teetering on the brink of extinction.

According to Wikipedia The Asiatic Cheetah is a critically endangered subspecies of the Cheetah found today only in Iran, with some occasional sightings in Balochistan, Pakistan.

It lives in its vast central desert in fragmented pieces of remaining suitable habitat. Although once common, the animal was driven to extinction in other parts of Southwest Asia from Arabia to India and Afghanistan.

Estimates based on field surveys over ten years indicate a remaining population of 70 to 100 Asiatic Cheetahs, most of them in Iran.

Source: http://www.greenprophet.com/2012/11/cheetahs-iran/

A small drop in one species’ population can drive others to actually die out

by Kate Shaw Yoshida

US Fish and Wildlife Service

When we think of extinction, we often picture the last individual of its kind leading a solitary life until its death marks the species’ disappearance from the face of the Earth. Called “numerical extinction,” this is the traditional concept of extinction, and it forms the basis for many conservation decisions.

But there is another type, called “functional extinction,” which takes a more ecological approach. Some scientists argue that the threshold for extinction should not be the complete disappearance of a species, but instead the point at which there aren’t enough individuals left in that species to perform whatever roles it was playing in the ecosystem. A species can be considered functionally extinct when its dwindling numbers cause another species in the same food web to disappear from the natural community first. These extinctions are important to understand since a species can go functionally extinct well before the population is small enough to put it in danger of a numerical extinction.

A recent theoretical paper in Nature demonstrates that functional extinctions occur at a surprisingly high frequency. The paper suggests that they should be considered when making conservation decisions and setting environmental policy.

Using both natural and computer-generated food webs, the researchers ran analytical models to examine how often functional extinctions happen and to identify the circumstances in which they occur. The model food webs were generated based on roles that species tend to play in real food webs, and they followed general rules common to most ecosystems (such as large animals being less abundant than smaller animals). In each web, the relationships between each species—such as who eats what, how much they eat, and how often—was either known (in the case of the natural webs) or calculated (in the case of the model webs).

To investigate what happens in a food web when a particular population declines, the researchers focused on each species separately and increased its mortality rate until an extinction occurred. If the species they manipulated was the one that disappeared, the extinction could be considered a numerical extinction; if a different species in the ecosystem disappeared as a result of the manipulation, the extinction was functional. The researchers found that functional extinctions happened at a surprisingly high rate: the probability of a functional extinction, compared to a numerical one, was 0.49 in the natural food webs and 0.72 in the model webs. In the authors’ words, “a species’ ecological functionality is often lost long before its existence is threatened.”

Furthermore, a species doesn’t have to be down to its last few straggling survivors in order to lose its ecological effectiveness. More than a quarter of the species in the natural food webs and more than half of those in the computer-generated webs became functionally extinct after losing just thirty percent of their population. That’s a pretty frightening statistic: a die-off of less than a third of a species’ members can unbalance an ecosystem enough to trigger the complete extinction of another species in the community.

Food webs are incredibly complicated and nuanced, and the results demonstrate the delicate balance of ecological communities. In the study, many of the species that disappeared as a result of a functional extinction weren’t even directly linked to the dying species in the food web. In other words, they were driven to extinction by a small decline in a species they don’t eat (and which doesn’t eat them).

Of course, this study was a simplistic representation of what goes on in actual ecological communities. However, if anything, it’s probably a conservative estimate of the damage that increasing mortality rates and decreasing population sizes can cause. In all likelihood, the effects of a changing world—including climate change, decreasing forest cover, and human-wildlife conflict—can wreak even more havoc on ecosystems than this study suggests.

The bright side is that understanding functional extinctions can inform our decisions about managing and conserving species. For instance, the researchers found that there is an inverse relationship between a species’ body mass and its tendency to go numerically, rather than functionally, extinct; the bigger an animal is, the more likely it is that increasing its mortality rate will drive another species to extinction. This type of knowledge could help prioritize where conservation efforts and resources should go. However, to make this type of information useful, scientists must continue to investigate extinction in a more ecological sense, and policymakers must be willing to take the results into account.

Nature, 2013. DOI: 10.1038/nature12277  (About DOIs).

Source: http://arstechnica.com/science/2013/07/not-yet-gone-but-effectively-extinct/