What is a ‘mass extinction’ and are we in one now?



Humans are probably causing what ice ages and asteroids caused before them.
Keith Roper/Flickr, CC BY-SA

Frédérik Saltré, Flinders University and Corey J. A. Bradshaw, Flinders University

For more than 3.5 billion years, living organisms have thrived, multiplied and diversified to occupy every ecosystem on Earth. The flip side to this explosion of new species is that species extinctions have also always been part of the evolutionary life cycle.

But these two processes are not always in step. When the loss of species rapidly outpaces the formation of new species, this balance can be tipped enough to elicit what are known as “mass extinction” events.




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A mass extinction is usually defined as a loss of about three quarters of all species in existence across the entire Earth over a “short” geological period of time. Given the vast amount of time since life first evolved on the planet, “short” is defined as anything less than 2.8 million years.

Since at least the Cambrian period that began around 540 million years ago when the diversity of life first exploded into a vast array of forms, only five extinction events have definitively met these mass-extinction criteria.

These so-called “Big Five” have become part of the scientific benchmark to determine whether human beings have today created the conditions for a sixth mass extinction.

An ammonite fossil found on the Jurassic Coast in Devon. The fossil record can help us estimate prehistoric extinction rates.
Corey Bradshaw, Author provided

The Big Five

These five mass extinctions have happened on average every 100 million years or so since the Cambrian, although there is no detectable pattern in their particular timing. Each event itself lasted between 50 thousand and 2.76 million years. The first mass extinction happened at the end of the Ordovician period about 443 million years ago and wiped out over 85% of all species.

The Ordovician event seems to have been the result of two climate phenomena. First, a planetary-scale period of glaciation (a global-scale “ice age”), then a rapid warming period.

The second mass extinction occurred during the Late Devonian period around 374 million years ago. This affected around 75% of all species, most of which were bottom-dwelling invertebrates in tropical seas at that time.

This period in Earth’s past was characterised by high variation in sea levels, and rapidly alternating conditions of global cooling and warming. It was also the time when plants were starting to take over dry land, and there was a drop in global CO2 concentration; all this was accompanied by soil transformation and periods of low oxygen.

To establish a ‘mass extinction’, we first need to know what a normal rate of species loss is.
from http://www.shutterstock.com

The third and most devastating of the Big Five occurred at the end of the Permian period around 250 million years ago. This wiped out more than 95% of all species in existence at the time.

Some of the suggested causes include an asteroid impact that filled the air with pulverised particle, creating unfavourable climate conditions for many species. These could have blocked the sun and generated intense acid rains. Some other possible causes are still debated, such as massive volcanic activity in what is today Siberia, increasing ocean toxicity caused by an increase in atmospheric CO₂, or the spread of oxygen-poor water in the deep ocean.

Fifty million years after the great Permian extinction, about 80% of the world’s species again went extinct during the Triassic event. This was possibly caused by some colossal geological activity in what is today the Atlantic Ocean that would have elevated atmospheric CO₂ concentrations, increased global temperatures, and acidified oceans.

The last and probably most well-known of the mass-extinction events happened during the Cretaceous period, when an estimated 76% of all species went extinct, including the non-avian dinosaurs. The demise of the dinosaur super predators gave mammals a new opportunity to diversify and occupy new habitats, from which human beings eventually evolved.

The most likely cause of the Cretaceous mass extinction was an extraterrestrial impact in the Yucatán of modern-day Mexico, a massive volcanic eruption in the Deccan Province of modern-day west-central India, or both in combination.



The Conversation, CC BY-ND

Is today’s biodiversity crisis a sixth mass extinction?

The Earth is currently experiencing an extinction crisis largely due to the exploitation of the planet by people. But whether this constitutes a sixth mass extinction depends on whether today’s extinction rate is greater than the “normal” or “background” rate that occurs between mass extinctions.

This background rate indicates how fast species would be expected to disappear in absence of human endeavour, and it’s mostly measured using the fossil record to count how many species died out between mass extinction events.

The Christmas Island Pipistrelle was announced to be extinct in 2009, years after conservationists raised concerns about its future.
Lindy Lumsden

The most accepted background rate estimated from the fossil record gives an average lifespan of about one million years for a species, or one species extinction per million species-years. But this estimated rate is highly uncertain, ranging between 0.1 and 2.0 extinctions per million species-years. Whether we are now indeed in a sixth mass extinction depends to some extent on the true value of this rate. Otherwise, it’s difficult to compare Earth’s situation today with the past.

In contrast to the the Big Five, today’s species losses are driven by a mix of direct and indirect human activities, such as the destruction and fragmentation of habitats, direct exploitation like fishing and hunting, chemical pollution, invasive species, and human-caused global warming.

If we use the same approach to estimate today’s extinctions per million species-years, we come up with a rate that is between ten and 10,000 times higher than the background rate.

Even considering a conservative background rate of two extinctions per million species-years, the number of species that have gone extinct in the last century would have otherwise taken between 800 and 10,000 years to disappear if they were merely succumbing to the expected extinctions that happen at random. This alone supports the notion that the Earth is at least experiencing many more extinctions than expected from the background rate.

An endangered Indian wild dog, or Dhole. Before extinction comes a period of dwindling numbers and spread.
from http://www.shutterstock.com

It would likely take several millions of years of normal evolutionary diversification to “restore” the Earth’s species to what they were prior to human beings rapidly changing the planet. Among land vertebrates (species with an internal skeleton), 322 species have been recorded going extinct since the year 1500, or about 1.2 species going extinction every two years.

If this doesn’t sound like much, it’s important to remember extinction is always preceded by a loss in population abundance and shrinking distributions. Based on the number of decreasing vertebrate species listed in the International Union for Conservation of Nature’s Red List of Threatened Species, 32% of all known species across all ecosystems and groups are decreasing in abundance and range. In fact, the Earth has lost about 60% of all vertebrate individuals since 1970.

Australia has one of the worst recent extinction records of any continent, with more than 100 species of vertebrates going extinct since the first people arrived over 50 thousand years ago. And more than 300 animal and 1,000 plant species are now considered threatened with imminent extinction.




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Although biologists are still debating how much the current extinction rate exceeds the background rate, even the most conservative estimates reveal an exceptionally rapid loss of biodiversity typical of a mass extinction event.

In fact, some studies show that the interacting conditions experienced today, such as accelerated climate change, changing atmospheric composition caused by human industry, and abnormal ecological stresses arising from human consumption of resources, define a perfect storm for extinctions. All these conditions together indicate that a sixth mass extinction is already well under way.




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The Conversation


Frédérik Saltré, Research Fellow in Ecology & Associate Investigator for the ARC Centre of Excellence for Australian Biodiversity and Heritage, Flinders University and 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

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

You can help track 4 billion bogong moths with your smartphone – and save pygmy possums from extinction



Healesville Sanctuary, Werribee Open Range Zoo

Sally Sherwen, University of Melbourne and Therésa Jones, University of Melbourne

Each year, from September to mid-October, the tiny and very precious mountain pygmy-possums arise from their months of hibernation under the snow and begin feasting on billions of bogong moths that migrate from Queensland to Victoria’s alpine region.

But for the past two springs, moth numbers have collapsed from around 4.4 billion in alpine areas to an almost undetectable number of individuals. And the mountain pygmy-possums went hungry, dramatically affecting breeding success among the last remaining 2,000 that live in the wild.




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This year’s migration of bogong moths to the possums’ alpine home is crucial for the critically endangered mountain pygmy-possums. That’s why we’re asking you to do two simple things: turn off your lights at night, and if you see a bogong moth, take a picture.

What’s happened to the moths?

Bogong moths make an epic migration through Australia every spring.
Credit: Donald Hobern

We don’t know exactly why the moths are not making it to their summer alpine destination. It’s likely extreme drought, pesticides and changes in agricultural practices are all major factors. However, scientists believe that because moths use both the Earth’s magnetic field and visual cues on the horizon to navigate, light pollution from urban centres can confuse the moths and stall their journey.

Some of the greatest beacons on their path are Parliament House and Canberra’s bright surrounds. Both parliamentarians and the general public are being asked to turn unnecessary outdoor lights off from September 1 to October 31, as part of the Lights Off for Moths campaign.

Artificial night lighting has dramatically changed the nocturnal environment. In urban environments, the soft glow of moonlight is overpowered by bright streetlights, security lights and car headlamps. These light sources can be more than 1,000 times as bright as moonlight, and their biological impact is increasingly visible and widespread.

One of the most obvious impacts of artificial light at night is that it can attract animals (sometimes fatally). While a “moth to a flame” may be somewhat poetic, when one moth becomes hundreds, or potentially thousands, the ecological impact may be catastrophic. Current global lighting practices may be creating this very scenario.

Recent evidence links the presence of artificial light at night with large-scale deaths and shifts in nocturnal migration patterns in birds. In insects, artificial night lighting disrupts nocturnal pollination networks and is strongly linked with observed mass declines in insect (and particularly moth) populations.

No moths means hungry possums

When a species like bogong moths decline, it has huge ramifications. Insects in particular are vital pillars supporting whole ecosystems – without bees and other insect pollinators, for example, we risk the extinction of our flowering plants. Many birds, reptiles and mammals depend on insects as part of their diet.

Tiny mountain pygmy possums, like many other animals, depend on the annual bogong moth migration for food.
Tim Bawden

For mountain pygmy possums, the fatty, nutrient-rich bounty of bogong moths arrives right as they are waking up in the spring. They are one of the only Australian mammals that hibernate, and can spend up to seven months sleeping under the alpine snow.

The possums awake ravenously hungry, and devour the bogong moths to regain crucial fat stores. Without the moths there at the right time, the possums struggle to secure enough energy to breed successfully.

Snap that moth

Alongside the Lights Off for Moths campaign, Zoos Victoria has launched Moth Tracker, an app that allows Australians to photograph and log any potential sightings of migrating bogong moths.

Moth Tracker, which can be accessed through any laptop or smartphone, is adapted from the popular Southern Right Whale watching app in collaboration with Federation University and Victorian conversation network SWIFFT.

Bogong moths migrate from their winter breeding grounds throughout Queensland, New South Wales and western Victoria in search of cooler climates for the spring and summer in the Victorian and NSW Alpine regions where the mountain pygmy-possums live.

Before they become moths, the larvae look like tiny, shiny brown capsules and are commonly referred to as cutworm. Migratory bogong moths are dark brown, with two lighter spots on each wing. They are small, only about the length of a paper clip. During the day they’re often seen grouped together like roof tiles. At night, they are more active and flying around.

If you see a bogong moth (or something you think might be a bogong month), we need you to take a photograph and log the location, day and time with Moth Tracker. Scientists will use the data to determine whether any moths are making their way to the precious, and very hungry, possums that are just starting to wake from their winter hibernation.




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The Victorian Mountain Pygmy-possum Recovery Team, together with partner organisations, is also investigating options for interventions in the wild if needed. These may include a world-first airdropping of “bogong balls” to feed the hungry possums, as well as improving habitat connectivity and captive measures to support populations through the breeding season.

But with unnecessary outdoor lights switched off and citizen scientists looking out for bogong moths, there is still hope for the mountain pygmy-possums.The Conversation

Sally Sherwen, Director Wildlife Conservation and Science, Zoos Victoria, University of Melbourne and Therésa Jones, Lecturer in Evolution and Behaviour, University of Melbourne

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

Environment laws have failed to tackle the extinction emergency. Here’s the proof



Koalas are among the threatened native species worst affected by habitat loss.
Taronga Zoo

Michelle Ward, The University of Queensland; April Reside, The University of Queensland; Hugh Possingham, The University of Queensland; James Watson, The University of Queensland; Jeremy Simmonds, The University of Queensland; Jonathan Rhodes, The University of Queensland, and Martin Taylor, The University of Queensland

Threatened species habitat larger than the size of Tasmania has been destroyed since Australia’s environment laws were enacted, and 93% of this habitat loss was not referred to the federal government for scrutiny, our new research shows.

The research, published today in Conservation Science and Practice, shows that 7.7 million hectares of threatened species habitat has been destroyed in the 20 years since the Environment Protection and Biodiversity Conservation (EPBC) Act 1999 came into force.

The Southern black throated finch, one of the threatened native animals worst affected by habitat loss.
Eric Vanderduys/BirdLife Australia



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Some 85% of land-based threatened species experienced habitat loss. The iconic koala was among the worst affected. More than 90% of habitat loss was not referred or submitted for assessment, despite a requirement to do so under Commonwealth environment laws.

Our research indicates the legislation has comprehensively failed to safeguard Australia’s globally significant natural values, and must urgently be reformed and enforced.

What are the laws supposed to do?

The EPBC Act was enacted in 1999 to protect the diversity of Australia’s unique, and increasingly threatened, flora and fauna. It was considered a giant step forward for biodiversity conservation and was expected to become an important legacy of the Howard Coalition government.

A dead koala outside Ipswich, Queensland. Environmentalists attributed the death to land clearing.
Jim Dodrill/The Wilderness Society



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The law aims to conserve so-called “protected matters” such as threatened species, migratory species, and threatened ecosystems.

Clearing and land use change is regarded by ecologists as the primary threat to Australia’s biodiversity. In Queensland, land clearing to create pasture is the greatest pressure on threatened flora and fauna.

Any action which could have a significant impact on protected matters, including habitat destruction through land clearing, must be referred to the federal government for assessment.

Loss of potential habitat for threatened species and migratory species, and threatened ecological communities. Dark blue represents habitat loss that has been assessed (or loss that occurred with a referral under the EPBC Act) and dark red represents habitat loss that has not been assessed (or loss that occurred without a referral under The Act). Three panels highlight the southern Western Australia coast (left), Tasmania (middle), and northern Queensland coast (right).
Adapted from Ward et al. 2019

The law is not being followed

We examined federal government forest and woodland maps derived from satellite imagery. The analysis showed that 7.7 million hectares of threatened species habitat has been cleared or destroyed since the legislation was enacted.

Of this area, 93% was not referred to the federal government and so was neither assessed nor approved.

Bulldozer clearing trees at Queensland’s Olive Vale Station in 2015.
ABC News, 2017

It is unclear why people or companies are not referring habitat destruction on such a large scale. People may be self-assessing their activities and concluding they will not have a significant impact.

Others may be seeking to avoid the expense of a referral, which costs A$6,577 for people or companies with a turnover of more than A$10 million a year.

The failure to refer may also indicate a lack of awareness of, or disregard for, the EPBC Act.

The biggest losers

Our research found that 1,390 (85%) of terrestrial threatened species experienced habitat loss within their range since the EPBC Act was introduced.

Among the top ten species to lose the most area were the red goshawk, the ghost bat, and the koala, losing 3 million, 2.9 million, and 1 million hectares, respectively.

In less than two decades, many other imperilled species have lost large chunks of their potential habitat. They include the Mount Cooper striped skink (25%), the Keighery’s macarthuria (23%) and the Southern black-throated finch (10%).

(a) The top 10 most severely impacted threatened species include those that have lost the highest proportion of their total habitat, and (b) species who have lost the most habitat, as mapped by the Federal Government.
Adapted from Ward et al. 2019

What’s working, what’s not

We found that almost all referrals to the federal government for habitat loss were made by urban developers, mining companies and commercial developers. A tiny 1.3% of referrals were made by agricultural developers – despite clear evidence that land clearing for pasture development is the primary driver of habitat destruction.

Alarmingly, even when companies or people did refer proposed actions, 99% were allowed to proceed (sometimes with conditions).

The high approval rates may be derived, in part, from inconsistent application of the “significance” test under the federal laws.

Hundreds of protesters gather in Sydney in 2016 to demand that New South Wales retain strong land clearing laws.
Dean Lewins/AAP

For example, in a successful prosecution in 2015, Powercor Australia and Vemco] were fined A$200,000 for failing to refer clearing of a tiny 0.5 hectares of a critically endangered ecosystem. In contrast, much larger tracts of habitat have been destroyed without referral or approval, and without any such enforcement action being taken.

Clearer criteria for determining whether an impact is significant would reduce inconsistency in decisions, and provide more certainty for stakeholders.

The laws must be enforced and reformed

If the habitat loss trend continues, two things are certain: more species will become threatened with extinction, and more species will become extinct.

The Act must, as a matter of urgency, be properly enforced to curtail the mass non-referral of actions that our analysis has revealed.

The left pie chart illustrates the breakdown of industries referring their actions by number of referrals; the right pie chart illustrates the breakdown of industries referring their actions by area (hectares). Both charts highlight the agricultural sector as a low-referring industry.
Adapted from Ward et al. 2019

If nothing else, this will help Australia meet its commitment under the Convention on Biological Diversity to prevent extinction of known threatened species and improve their conservation status by 2020.




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Mapping the critical habitat essential to the survival of every threatened species is also an important step. The Act should also be reformed to ensure critical habitat is identified and protected, as happens in the United States.

Australia is already a world leader in modern-day extinctions. Without a fundamental change in how environmental law is written, used, and enforced, the crisis will only get worse.The Conversation

Michelle Ward, PhD Student, The University of Queensland; April Reside, Researcher, Centre for Biodiversity and Conservation Science, The University of Queensland; Hugh Possingham, Professor, The University of Queensland; James Watson, Professor, The University of Queensland; Jeremy Simmonds, Postdoctoral Research Fellow in Conservation Science, The University of Queensland; Jonathan Rhodes, Associate Professor, The University of Queensland, and Martin Taylor, Adjunct senior lecturer, The University of Queensland

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

Plants are going extinct up to 350 times faster than the historical norm



Plant extinctions have skyrocketed, driven in large part by land clearing and climate change.
Graphic Node/Unsplash, CC BY-SA

Jaco Le Roux, Macquarie University; Florencia Yanelli, Stellenbosch University; Heidi Hirsch, Stellenbosch University; José María Iriondo Alegría, Universidad Rey Juan Carlos; Marcel Rejmánek, University of California, Davis, and Maria Loreto Castillo, Stellenbosch University

Earth is seeing an unprecedented loss of species, which some ecologists are calling a sixth mass extinction. In May, a United Nations report warned that 1 million species are threatened by extinction. More recently, 571 plant species were declared extinct.

But extinctions have occurred for as long as life has existed on Earth. The important question is, has the rate of extinction increased? Our research, published today in Current Biology, found some plants have been going extinct up to 350 times faster than the historical average – with devastating consequences for unique species.




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Measuring the rate of extinction

“How many species are going extinct” is not an easy question to answer. To start, accurate data on contemporary extinctions are lacking from most parts of the world. And species are not evenly distributed – for example, Madagascar is home to around 12,000 plant species, of which 80% are endemic (found nowhere else). England, meanwhile, is home to only 1,859 species, of which 75 (just 4%) are endemic.

Areas like Madagascar, which have exceptional rates of biodiversity at severe risk from human destruction, are called “hotspots”. Based purely on numbers, biodiversity hotspots are expected to lose more species to extinction than coldspots such as England.

But that doesn’t mean coldspots aren’t worth conserving – they tend to contain completely unique plants.

We are part of an international team that recently examined 291 modern plant extinctions between biodiversity hot- and coldspots. We looked at the underlying causes of extinction, when they happened, and how unique the species were. Armed with this information, we asked how extinctions differ between biodiversity hot- and coldspots.

Unsurprisingly, we found hotspots to lose more species, faster, than coldspots. Agriculture and urbanisation were important drivers of plant extinctions in both hot- and coldspots, confirming the general belief that habitat destruction is the primary cause of most extinctions. Overall, herbaceous perennials such as grasses are particularly vulnerable to extinction.

However, coldspots stand to lose more uniqueness than hotspots. For example, seven coldspot extinctions led to the disappearance of seven genera, and in one instance, even a whole plant family. So clearly, coldspots also represent important reservoirs of unique biodiversity that need conservation.

We also show that recent extinction rates, at their peak, were 350 times higher than historical background extinction rates. Scientists have previously speculated that modern plant extinctions will surpass background rates by several thousand times over the next 80 years.

So why are our estimates of plant extinction so low?

First, a lack of comprehensive data restricts inferences that can be made about modern extinctions. Second, plants are unique in – some of them live for an extraordinarily long time, and many can persist in low densities due to unique adaptations, such as being able to reproduce in the absence of partners.

Let’s consider a hypothetical situation where we only have five living individuals of Grandidier’s baobab (Adansonia grandidieri) left in the wild. These iconic trees of Madagascar are one of only nine living species of their genus and can live for hundreds of years. Therefore, a few individual trees may be able to “hang in there” (a situation commonly referred to as “extinction debt”) but will inevitably become extinct in the future.

Finally, declaring a plant extinct is challenging, simply because they’re often very difficult to spot, and we can’t be sure we’ve found the last living individuals. Indeed, a recent report found 431 plant species previously thought to be extinct have been rediscovered. So, real plant extinction rates and future extinctions are likely to far exceed current estimates.

There is no doubt that biodiversity loss, together with climate change, are some of the biggest challenges faced by humanity. Along with human-driven habitat destruction, the effects of climate change are expected to be particularly severe on plant biodiversity. Current estimates of plant extinctions are, without a doubt, gross underestimates.




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However, the signs are crystal clear. If we were to condense the Earth’s 4.5-billion-year-old history into one calendar year, then life evolved somewhere in June, dinosaurs appeared somewhere around Christmas, and the Anthropocene starts within the last millisecond of New Year’s Eve. Modern plant extinction rates that exceed historical rates by hundreds of times over such a brief period will spell disaster for our planet’s future.The Conversation

Jaco Le Roux, Associate Professor, Macquarie University; Florencia Yanelli, Researcher, Stellenbosch University; Heidi Hirsch, Postdoctoral research fellow, Stellenbosch University; José María Iriondo Alegría, Catedrático de universidad en el área de Botánica, Universidad Rey Juan Carlos; Marcel Rejmánek, Emeritus professor, University of California, Davis, and Maria Loreto Castillo, PhD Candidate, Stellenbosch University

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