Did People Or Climate Kill Off The Megafauna?

Did People Or Climate Kill Off The Megafauna? When freshwater dried up, so did many megafauna species. Centre of Excellence for Australian Biodiversity and Heritage, Author provided

Earth is now firmly in the grips of its sixth “mass extinction event”, and it’s mainly our fault. But the modern era is definitely not the first time humans have been implicated in the extinction of a wide range of species.

In fact, starting about 60,000 years ago, many of the world’s largest animals disappeared forever. These “megafauna” were first lost in Sahul, the supercontinent formed by Australia and New Guinea during periods of low sea level.

The causes of these extinctions have been debated for decades. Possible culprits include climate change, hunting or habitat modification by the ancestors of Aboriginal people, or a combination of the two.

The main way to investigate this question is to build timelines of major events: when species went extinct, when people arrived, and when the climate changed. This approach relies on using dated fossils from extinct species to estimate when they went extinct, and archaeological evidence to determine when people arrived.

Comparing these timelines allows us to deduce the likely windows of coexistence between megafauna and people.

We can also compare this window of coexistence to long-term models of climate variation, to see whether the extinctions coincided with or shortly followed abrupt climate shifts.

Data drought

One problem with this approach is the scarcity of reliable data due to the extreme rarity of a dead animal being fossilised, and the low probability of archaeological evidence being preserved in Australia’s harsh conditions.

This means many studies are restricted to making conclusions regarding drivers of extinction at the scale of single palaeontological sites or of specific archaeological sites.

Alternatively, timelines can be constructed by including evidence across large spatial scales, such as over the entire continent of Australia.

Unfortunately, this “lumping” of the available evidence across many different sites disregards the variation in the relative contribution of different extinction drivers across the landscape.

Mapping extinction

In our research published in Nature Communications, we developed advanced mathematical tools to map the regional patterns of the timing of megafauna disappearances and the arrival of Aboriginal ancestors across south-eastern Australia.

Based on these new maps, we can now work out where humans and megafauna coexisted, and where they did not.

Did People Or Climate Kill Off The Megafauna? Areas of coexistence and non-coexistence between humans and megafauna. F. Saltré

It turns out humans coexisted with the megafauna over about 80% of south-eastern Sahul for up to 15,000 years, depending on the region in question.

In other regions such as Tasmania, there was no such coexistence. This rules out humans as a likely driver of megafauna extinction in those areas.

We then aligned these windows of coexistence and non-coexistence in each part of the landscape with several environmental measures derived from climate simulations over the past 120,000 years. This gave us an idea about which factors best explained the timing of megafauna extinction in each part of the landscape.

Despite a major effect on extinctions in areas where megafauna and people did not coexist, there was nothing at all to explain the timing of megafauna extinctions in places where megafauna and people coexisted.

This surprising result suggested that we had missed something important in our analyses.

Connecting the dots

The major flaw in our approach was to analyse each location independently of its surroundings. Our initial model had failed to take account of the fact that an extinction in one place can affect an extinction in another location nearby.

Once we changed our model to incorporate these effects, the real picture finally emerged. We found that megafauna extinctions in areas were they coexisted with humans were most likely caused by a combination of human pressure and access to water.

In the other 20% of the landscape, where humans and megafauna did not coexist, we found that extinctions likely occurred because of a lack of plants, driven by increasingly dry conditions. This doomed many plant-eating megafauna species to extinction.

Did People Or Climate Kill Off The Megafauna? Relative importance (in %) of variables best describing the timing (first row) and the directional gradient (second row) of megafauna extinction in areas of non-coexistence (first column) and coexistence (second column) of people and megafauna. F. Saltré

Space is key

This is the first evidence that tens of thousands of years ago, the combination of humans and climate change was already making species more likely to disappear. Yet this pattern was invisible if we ignored the interconnectedness of the various regions involved.

This might be just the beginning we need for a new, more nuanced treatment of environmental change in the deep past in other regions of the world.

More importantly, our results reinforce scientists’ stark warning about the immediate future of our planet’s plants and wildlife. Given rising human pressures on the natural world, coupled with an unprecedented pace of global warming, modern species are facing similar ravages.The Conversation

About The Author

Frédérik Saltré, Research Fellow in Ecology & Associate Investigator for the ARC Centre of Excellence for Australian Biodiversity and Heritage, Flinders University; Corey J. A. Bradshaw, Matthew Flinders Fellow in Global Ecology and Models Theme Leader for the ARC Centre of Excellence for Australian Biodiversity and Heritage, Flinders University, and Katharina J. Peters, Postdoctoral Fellow, Flinders University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Related Books

Life After Carbon: The Next Global Transformation of Cities

by Peter Plastrik , John Cleveland
1610918495The future of our cities is not what it used to be. The modern-city model that took hold globally in the twentieth century has outlived its usefulness. It cannot solve the problems it helped to create—especially global warming. Fortunately, a new model for urban development is emerging in cities to aggressively tackle the realities of climate change. It transforms the way cities design and use physical space, generate economic wealth, consume and dispose of resources, exploit and sustain the natural ecosystems, and prepare for the future. Available On Amazon

The Sixth Extinction: An Unnatural History

by Elizabeth Kolbert
1250062187Over the last half-billion years, there have been Five mass extinctions, when the diversity of life on earth suddenly and dramatically contracted. Scientists around the world are currently monitoring the sixth extinction, predicted to be the most devastating extinction event since the asteroid impact that wiped out the dinosaurs. This time around, the cataclysm is us. In prose that is at once frank, entertaining, and deeply informed, New Yorker writer Elizabeth Kolbert tells us why and how human beings have altered life on the planet in a way no species has before. Interweaving research in half a dozen disciplines, descriptions of the fascinating species that have already been lost, and the history of extinction as a concept, Kolbert provides a moving and comprehensive account of the disappearances occurring before our very eyes. She shows that the sixth extinction is likely to be mankind's most lasting legacy, compelling us to rethink the fundamental question of what it means to be human. Available On Amazon

Climate Wars: The Fight for Survival as the World Overheats

by Gwynne Dyer
1851687181Waves of climate refugees. Dozens of failed states. All-out war. From one of the world’s great geopolitical analysts comes a terrifying glimpse of the strategic realities of the near future, when climate change drives the world’s powers towards the cut-throat politics of survival. Prescient and unflinching, Climate Wars will be one of the most important books of the coming years. Read it and find out what we’re heading for. Available On Amazon

From The Publisher:
Purchases on Amazon go to defray the cost of bringing you InnerSelf.comelf.com, MightyNatural.com, and ClimateImpactNews.com at no cost and without advertisers that track your browsing habits. Even if you click on a link but don't buy these selected products, anything else you buy in that same visit on Amazon pays us a small commission. There is no additional cost to you, so please contribute to the effort. You can also use this link to use to Amazon at any time so you can help support our efforts.

 

enafarzh-CNzh-TWdanltlfifrdeiwhihuiditjakomsnofaplptruesswsvthtrukurvi

follow InnerSelf on

facebook-icontwitter-iconrss-icon

 Get The Latest By Email

{emailcloak=off}

LATEST VIDEOS

Five Climate Disbeliefs: A Crash Course In Climate Misinformation
The Five Climate Disbeliefs: A Crash Course In Climate Misinformation
by John Cook
This video is a crash course in climate misinformation, summarizing the key arguments used to cast doubt on the reality…
The Arctic Hasn't Been This Warm For 3 Million Years and That Means Big Changes For The Planet
The Arctic Hasn't Been This Warm For 3 Million Years and That Means Big Changes For The Planet
by Julie Brigham-Grette and Steve Petsch
Every year, sea ice cover in the Arctic Ocean shrinks to a low point in mid-September. This year it measures just 1.44…
What Is A Hurricane Storm Surge and Why Is It So Dangerous?
What Is A Hurricane Storm Surge and Why Is It So Dangerous?
by Anthony C. Didlake Jr
As Hurricane Sally headed for the northern Gulf Coast on Tuesday, September 15, 2020, forecasters warned of a…
Ocean Warming Threatens Coral Reefs and Soon Could Make It Harder To Restore Them
Ocean Warming Threatens Coral Reefs and Soon Could Make It Harder To Restore Them
by Shawna Foo
Anyone who’s tending a garden right now knows what extreme heat can do to plants. Heat is also a concern for an…
Sunspots Do Affect Our Weather But Not As Much As Other Things
Sunspots Do Affect Our Weather But Not As Much As Other Things
by Robert McLachlan
Are we headed for a period with lower Solar activity, i.e. sunspots? How long will it last? What happens to our world…
Dirty Tricks Climate Scientists Faced In Three Decades Since First IPCC Report
Dirty Tricks Climate Scientists Faced In Three Decades Since First IPCC Report
by Marc Hudson
Thirty years ago, in a small Swedish city called Sundsvall, the Intergovernmental Panel on Climate Change (IPCC)…
Methane Emissions Hit Record Breaking Levels
Methane Emissions Hit Record Breaking Levels
by Josie Garthwaite
Global emissions of methane have reached the highest levels on record, research shows.
kelp forrest 7 12
How The Forests Of The World’s Oceans Contribute To Alleviating The Climate Crisis
by Emma Bryce
Researchers are looking to kelp for help storing carbon dioxide far beneath the surface of the sea.

LATEST ARTICLES

Creative Destruction: The Covid-19 Economic Crisis Is Accelerating the Demise of Fossil Fuels
Creative Destruction: The Covid-19 Economic Crisis Is Accelerating the Demise of Fossil Fuels
by Peter Newman
Creative destruction “is the essential fact about capitalism”, wrote the great Austrian economist Joseph Schumpeter in…
Global Emissions Are Down By An Unprecedented 7% — But Don’t Start Celebrating Just Yet
Global Emissions Are Down By An Unprecedented 7% — But Don’t Start Celebrating Just Yet
by Pep Canadell et al
Global emissions are expected to decline by about 7% in 2020 (or 2.4 billion tonnes of carbon dioxide) compared to 2019…
Decades of Unsustainable Water Use Has Dried Up Lakes and Caused Environmental Destruction
Decades of Unsustainable Water Use Has Dried Up Lakes and Caused Environmental Destruction in Iran
by Zahra Kalantari et al
Salt storms are an emerging threat for millions of people in north-western Iran, thanks to the catastrophe of Lake…
Climate Sceptic or Climate Denier? It's Not That Simple and Here's Why
Climate Sceptic or Climate Denier? It's Not That Simple and Here's Why
by Peter Ellerton
Climate change is now climate crisis and a climate sceptic now a climate denier, according to the recently updated…
The 2020 Atlantic Hurricane Season Was A Record-Breaker, and It's Raising More Concerns About Climate Change
The 2020 Atlantic Hurricane Season Was A Record-Breaker, and It's Raising More Concerns About Climate Change
by James H. Ruppert Jr. and Allison Wing
We’re looking back at a trail of broken records, and the storms may still not be over even though the season officially…
Why Climate Change Is Making Autumn Leaves Change Colour Earlier
Why Climate Change Is Making Autumn Leaves Change Colour Earlier
by Philip James
Temperature and day length were traditionally accepted as the main determinants of when leaves changed colour and fell,…
Take Caution: Winter Drownings May Increase As Ice Thins With Climate Change
Take Caution: Winter Drownings May Increase As Ice Thins With Climate Change
by Sapna Sharma
Every winter, the ice that forms on lakes, rivers and oceans, supports communities and culture. It provides…
There Are No Time-Travelling Climatologists: Why We Use Climate Models
There Are No Time-Travelling Climatologists: Why We Use Climate Models
by Sophie Lewis and Sarah Perkins-Kirkpatrick
The first climate models were built on fundamental laws of physics and chemistry and designed to study the climate…