Sixth mass extinction just around the corner?

Following on from the videos I posted last week, my post today is going to focus on a recent paper by Barnosky et al. (2011).  Barnosky provides a detailed background to previous mass extinctions and also  focuses on arguments surrounding the possibility of a sixth mass extinction.

What is a mass extinction?

The answer lies in the past. Palaeontologists characterise a mass extinction as a short geological period in Earth's history where more than 75% of estimated species become extinct (Jablonski, 1994).  This type of extinction has only happened 5 times in the past 540 million years (Barnosky et al. 2011). The 5 mass extinctions occurred at the end of the Ordovician, Devonian, Permian, Triassic and Cretaceous periods. Will the anthropocene hold the next mass extinction?

Biodiversity of the planet over time, showing the five mass extinctions in history.
Graph adapted from Wilson (1992)

Why do we care about past extinctions?

Scientists are interested in past extinctions because they provide a key to the future. The most famous species extinction was the Cretaceous- Tertiary which occurred 65 million years ago. This is the extinction that is famed for the death of the dinosaurs. One hypothesis for this decline was climatic cooling causing a reduction in hospitable habitats (this is the worry for current global warming). The Permian extinction (248 million years ago) also causes scientists to quake in their boots due to being caused mainly by global environmental change, including methane release from the sea floor, increased sea level and a shift in ocean circulation (Eldredge, 2011). The main concern is that history will repeat itself? Increasingly, academics are recognising contemporary species extinctions as part of an overarching 'sixth mass extinction'. Anthropogenic influences such as habitat fragmentation, disruption by invasive species and changing global climate all directly contribute to the decline of biodiversity. Scientists are now worried that the Earth will, in a few centuries, be under threat from major species decline.

Before we can come to any sort of conclusions, it remains vital to establish the current situation within the context of  previous mass extinctions. There have been many landmark studies that have told of modern extinction rates an order of magnitude higher than than previous extinction rates (Doubleday, 1992; May et al. 1995). The below chart explores the extinction magnitudes of IUCN assessed taxa in comparison to the 75% benchmark (International Union of Conservation Red List, 2010).  The black icons add the species that are currently 'threatened' species to those that have been extinct for over the past 500 years. Therefore, we can see that all species are threatened in the age of the anthropocene. Groupings such as mammals, birds and amphibians, which have had historically the lowest percentages of species extinctions, nowadays have the highest numbers of endangered and threatened species. Could these species be susceptible to catastrophic extinctions? The current numbers show the sixth mass extinction is looming quite far away, however anthropogenic activities are causing more and more species to become increasingly threatened. Barnosky et al. (2011) suggests that if all 'threatened' species disappeared we would be half way towards a possible anthropocene mass extinction.

Extinction magnitudes of IUCN assessed taxa (2010)

It is not just terrestrial species that are vulnerable, marine species are particularly susceptible to mass extinction. At least 830 marine species have been classified as critically endangered, endangered or vulnerable. Assessments for marine species are lagging behind those for terrestrial species. However, the IUCN aimed to have 20,000 marine species assessed by 2012. It is important to understand that the past drivers of extinction in the oceans are the same as the current threats  (as can be seen in the chart below).  Marine scientists that released the State of the Ocean 2013 report on 3rd October 2013, gave a warning stating 'we are entering an unknown territory of marine ecosystem change, and exposing organisms to intolerable evolutionary pressure. The next mass extinction event may have already begun'. The report explains how the ocean is the world's largest carbon sink and the increasing carbon dioxide levels are creating a 'deadly trio of impacts' including ocean acidification, ocean warming and deoxygenation all of which are threatening marine biodiversity. If you want to know more about this , check out The AnthropoSea, a blog dedicated to investigating the 'deadly trio' and its threat to marine biodiversity. 

What is the situation today? 

Today, the rapidly changing atmospheric conditions and warming of above average interglacial temperatures cause species to become vulnerable. With rising carbon dioxide levels, habitat destruction, pollution, overfishing, over hunting and invasive species, the world now has more ecological stressors than many species have ever experienced before. 

Species extinctions rising with increasing human populations.

The worrying question is how will this affect the already threatened species? It seems quite plausible that if humanity carries on living in the same way, it will not be long before the 'sixth mass extinction' is just around the corner.  It is encouraging that there is still much of Earth's biodiversity that can be saved. However, it is daunting that in order to save such species there must be rapid reversal of escalating threats. How realistic is this? 

While I was researching for this blog post I came across a very interesting short film that had just been released called the 'Last Hours'. The film had been produced for presentation at COP21 (the 21st session of the Conference of the parties to the UNFCCC expected to take place in 2015). The film maker was Thom Hardmann, an American radio talk show host and best selling novelist. I watched the film and I have to say although highly dramatised, with a soundtrack that could rival 'the day after tomorrow', it provides an insight into the possibility of another mass extinction.  The film has caused a media outpour, with the likes of Leonardo DiCaprio tweeting his affection for the film (thats the reason we know it is worth a watch!). 

However, the film has also received criticism for its methane hydrates hypothesis. In the recent IPCC 2013 report, many of the catastrophic changes being forecast were described as likely, unlikely or exceptionally unlikely. The melting of permafrost and the subsequent release of huge reservoirs of methane is deemed exceptionally unlikely, therefore the film has to be taken with a pinch of salt. Why not have a look and make your own judgements. 

Do you think we are in a sixth mass extinction, or are we very close to entering one? 

To end this post here is just a snapshot of some news articles that have documented species extinctions and the catastrophic possibility of another mass extinction.

Ananthaswamy, A (2004) 'Earth faces sixth mass extinction', New Scientist. 

Harvey, F (2013) 'Rate of ocean acidification due to carbon emissions is highest for 300 million years', UK Guardian.

IUNC (2009) 'Wildlife crisis worse than economic crisis', IUNC. 

Mccarthy, M (2011) 'Marine life facing mass extinction within one human generation', Independent. 

Pappas, S (2012) ' Earth's ecosystems nearing catastrophic "tipping point" warn scientists', The  Christian Science Monitor. 

Score board update. 

                                    Anthropocene 1- 0 Biodiversity 

The 6th Mass Extinction?

Hope you have all had a good weekend, despite the rain. I am posting a video to hopefully relief the boredom of staying indoors (unless you're outside braving the weather!) My next post will be focused on the arguments surrounding a possible '6th mass extinction'. Therefore, I thought the following video would be a good introduction of what is to come later next week. So grab a cup of tea, snuggle up in the warmth and enjoy.

Are we facing a sixth mass extinction- A short introduction

Invader Intolerance: A presumptuous viewpoint?

As my introductory post touched upon, there are many anthropogenic impacts effecting biodiversity (see below for a comprehensive list!). 

- Habitat destruction and fragmentation

- Agricultural intensification and changes in land use

- Changes in forest management practices

- Overfishing

- Atmospheric pollution

- Water pollution

- Climate change

- Human disturbance

- Invasive species

- Harvesting and collection of species (hunting)

- Ocean acidification

(Natural England, 2011) 

The focus for today is invasive species. Before I start chattering on about zebra mussels and the red squirrel, I believe it is crucial to understand just how scientists define and quantify biodiversity. The term 'biodiversity' originates from conservation biology and was coined by Walter Rosen in 1985. A formal definition was published by the Convention of Biological Diversity (1992) which stated:

'Biodiversity is the variability among living organisms including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems'. 

Biodiversity measures have, however, also taken a battering over the years.  Wilson (1992) discussed the ambiguity surrounding measures of diversity and explored the possibility that biodiversity was in fact restricted by measuring species numbers alone. This has also been reiterated more recently by (McCann, 2007).  Nowadays there is still uncertainty when quantifying biodiversity (scientists can never make up their minds) and therefore this will be considered in much greater detail in a few weeks. 

So now back to the purpose of this post- 'INVASIVE SPECIES'. Although known worldwide as threatening and disruptive, non-native species and their impacts to biodiversity continue to be greatly debated throughout scientific literature. So why do invasive species have such a bad reputation? Invasive, known also as 'alien' and 'non- native' species can have significant effects on the existence of some species and their habitats. An example is the native red squirrel (Sciurus vulgaris) which has become threatened and outcompeted in the UK by the non-native 'grey' squirrel (Sciurus carolinensis). The first evidence of the red squirrel dates back to the end of the last ice age, 10,000 years ago. 

Save our native: The Red Squirrel

However, since the grey squirrel became introduced to the UK in the 19th Century it has replaced the red squirrel throughout most of England, Wales and parts of Scotland and Ireland (Bryce, 1997). The traditional explanation for this reduction in the red squirrel, is the overwhelming competition with the grey squirrel for food resources (Kenward and Holm, 1993). This was not the only reason for their gradual decline, another proposal is the introduction of devastation parapoxvirus (a fatal strand of squirrel "pox") that was brought from North America to the UK by the grey squirrel. The disease spread into the red squirrel population hence the rate of infection was extremely high. This induced a population crash, reducing the crowding pressures on non-native grey squirrels which subsequently increased in numbers (Gurnell et al. 2004). 

Squirrel distribution maps from 1945- 2010 showing the interaction between the red and grey squirrels (RSST, n/d). 

From the above maps, the red squirrel population can be seen to be rapidly declining especially in Northern England and Wales, with the grey squirrel taking over the South of England and the Eastern Coast of Wales. Wales and the the midlands, surprisingly, have habitats which are occupied by both species. From the maps above it is highlighted that urgent steps are needed to address the issue of invasive species in order to save native species. 

It is not just terrestrial ecosystems that can become jeopardised by non-native species, freshwater habitats are also extremely vulnerable. The ICAIS (International conference on aquatic invasive species) 2013 report stated that 'the introduction and spread of invasive species in freshwater and marine environments is a worldwide problem that is increasing in frequency'. A recent example is the invasion of the Asian Carp throughout the river systems of Illinois, USA. They were introduced, from China, into water treatment ponds to remove algae in 1970s. The carp escaped and migrated northwards through the Mississippi and Illinois rivers. Although the carp did not cause any extinctions of native species, there was a decline of certain commercial fish such as the big mouth buffalo (Ictiobus cyprinellus). 

Bigmouth buffalo threatened...

Invasive species (in some cases) are considered such a colossal threat because they have the upper hand when resources become scarce.  CSIRO, Australia's national science agency calls invasive species 'one of the greatest threats to biodiversity and to the ecological and economic well being of society and the planet'.

However... not every scientist shares the same assertive view on invasive species. In fact, only a week ago Professor Phil Roberts from the University of York published a paper which throws all opinions up in the air. This is why I love science, its contestable nature. Roberts (2013) discusses how the Anthropocene could raise biological diversity through the introduction of non-native species causing evolutionary hybridisation. He acknowledges that some invasive species damage ecosystems and can eradicate resident species (as I have already explored). However, his discussion remains focused on how people fail to acknowledge that invasive species can also be positive for biodiversity. On average, less than one native species dies out for each introduced species that becomes established. Roberts (2013) neglects cases of invasive species disruption and instead highlights that, despite the fact that we are losing irreplaceable populations, in some (some being the key word here) regions biodiversity is actually increasing.

I will leave you with Roberts (2013) departing words: 

'we have to rethink our "irrational" dislike of invading species'.

I, on the other hand, do not believe that the negative reputation of invasive species is 'irrational', due to the destruction they can and have previously caused. However, it is vital to understand both arguments in order to judge whether there is still hope for biodiversity, in particular at a regional level, despite the doom and gloom of inevitable global species decline.

Anthropocene 0-0 Biodiversity 

What do you think is in the lead? Suggestions welcome!

 

Biodiversity vs 'The Anthropocene': Let the battle commence

Despite my initial inhibitions, I have finally joined the blogging world (enter applause here). Since this is my first post, I am going to explain the focus of my blog and why I believe it warrants such discussion. As my title, 'Is the grass greener on the other side?' suggests, I will be investigating debates surrounding the Anthropocene and its effect on global biodiversity. Are we entering a 6th mass extinction or is there still hope for the species that roam our planet? Roberts (2013) discusses how the Anthropocene has brought an age of 'ecological transformations' and my blog will explore the impacts of these 'transformations' for global biodiversity. My reasoning for choosing this focus, is probably due to my slight obsession with ecology (I love plants, what can I say). 

So what is the Anthropocene I hear you say? A simple definition can be found in the Oxford English Dictionary:

'relating to or denoting the current geological age, viewed as the period during which human activity has been been the dominant influence on climate and the environment'.

As is suggested, the Anthropocene is unlike any geological period before. The dangerous levels of industrialisation, land use change, ocean acidification, freshwater eutrophication, carbon dioxide and methane emissions are what distinguish this 'Age of the Humans'. Humanity has taken on the role of God and is now pushing the Earth over planetary boundaries. The exact time when the Anthropocene emerged still remains a highly contentious debate. For a VERY basic explanation of the Anthropocene and its implications, feel free to watch the following short video.

Over the course of my blog I aim to cover a wide range of topics including (but not limiting myself to) invasive species, ecosystem resilience, migration of species with climate change, ocean acidification, freshwater eutrophication and the 6th mass extinction. Rather than having a strict agenda, I want my blog to be an engagement with current literary debates and allow my opinions freedom to develop over the next 3 months. 

I hope you enjoy following the battle between biodiversity and the Anthropocene. What will come out on top? Will the grass for biodiversity be greener on the other side? 

Let the battle commence.