Has the Earth’s 6thmass extinction already arrived?
Barnosky, et al. 2011. Nature 471: 51-57
Blog by Willow
Authors (first 3 only)
Anthony Barnosky
PhD 1983 U.Washington
Prof. Biology at Stanford (since 2018), Prof. Emeritus at UC Berkeley (1990-2016)
“Ever-increasing numbers of people, climate change, and transformation of half of the planet’s land to serve humans are among the many pressures that are hallmarks of the unique time in which we now live, the Anthropocene. My current work focuses on understanding how to guide biological systems such that they maintain vibrancy in the face of unusually rapid human-caused global changes.”
Nicholas Matzke
PhD 2013 UC Berkeley
Discovery Early Career Award Research Fellow at the Australian National University
Wishes to “reintegrate” ecological and historical biogeography by looking at how environmental and ecological controls on dispersal have affected geographic range evolution through time and through phylogeny.
Susumu Tomiya
PhD 2013? UC Berkeley
Postdoc Des Moines University, previously Field Museum
"I study the fossil record of North American mammals, to understand how mammalian 'communities' are assembled and how they respond to major environmental changes at the macroevolutionary time scale of millions of years."
Paper Summary
Main Question
Do current rates and magnitudes of extinction qualify as a mass extinction compared to the Big Five?
Background
Mass Extinction- 75% of species disappear within 2 million years
Rate- # of extinctions/time
Magnitude- % of species that have gone extinct
Data biases
Geography- fossils don’t preserve everywhere, so you can’t compare everywhere
Sampling- only taxa with identifiable hard parts fossilize, and only animals we know are threatened get studied and not all consistently
Taxonomy- fossil species are usually morphological, modern species have a much wider range of definitions resulting in many more species than possible in fossils
Underestimating extinctions- the last fossil to appear is certainly not the last individual to go extinct, not all modern species are described let alone analyzed
Time- the fossil record is highly time-averaged compared to the modern, so all modern rates must be super-scaled up
Methods
Calculated rate, magnitude, and total extinction rate (rate plus magnitude) for the Big Five extinctions
Calculated rat, magnitude, and total extinction rate for the modern at a variety of assumptions and time scales
Results/Discussion
Modern rates of extinction is higher than background rates regardless of which IUCN animals go extinct. We are going extinct much faster than normal.
Modern magnitudes of extinction are at 20-43% of Big Five levels. We are not currently in a mass extinction.
Combined rates of extinction indicate we are going extinct slower to almost as fast as the Big Five.
If extinction rate continues, we could hit the 6thmass extinction between 240-540 yrs (worst case scenario). Conservative estimates place the 6thmass extinction between 4500-11000 yrs.
Conclusions
Technically, we are not yet in a mass extinction.
If we lose the “critically endangered” species, we will be in a mass extinction.
We have “primed the pump” of extinction and, without human mitigation efforts, stressors will increase in the future and intensify the already terrifying extinction looming ahead.
Remarks
This was nice and scary for just after Halloween. I liked how this paper was set up. I found Table 1 to be very interesting. The K-Pg extinction (dinosaurs) is usually everyone’s favorite extinction, so I’ve never really read about the others. First time I read the causes, I found too many similarities with projected climate change, so I also enjoyed the section about “Perfect Storms.”
This was really interesting to consider the requirements to be considered mass extinctions and the magnitude of them. It also gives me more appreciation to the amount of species lost during a mass extinction when comparing it to what we see today when the species being lost already seems critical.
ReplyDeleteI'm going to play devil's advocate here... Should we really be spending our time debating whether or not humans are causing a sixth mass extinction, or should we be spending that time, energy, and money, actively pursuing solutions? There are certainly many important things to learn from the past. However, I don't see how projecting current extinction rates is useful.
ReplyDeleteI agree with Willow about the qualifications of a "perfect storm" seeming more likely, even in the 7 year since Barnosky wrote the paper. It is all very disconcerting, and even if the recent species loss doesn't fit the 75% to hit a "mass extinction", it still reflects a huge amount of biodiversity lost. Also, I think this type of research is critical to getting people serious about pursuing solutions. Recently, the WWF report (https://www.bbc.com/news/science-environment-46028862?ocid=socialflow_facebook&ns_source=facebook&ns_mchannel=social&ns_campaign=bbcnews) made the rounds with its most recent survey of human impact globally. While headlines and news agencies might inflate results to get attention, the key issue is that attention still needs to be gathered, especially in the US.
ReplyDeleteIt's pretty interesting how we always talk about loss of species in recent years but it is not even comparable to the mass extinctions. But it is pretty useful to emphasize on it, or else not many people would be interested in conservation. Figure 2 is really cool. It puts many groups next to each other to show where they are compared to the 75% bench mark.
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ReplyDeleteThe sixth extinction will have more precise data with a greater explanation of how it gets to that point. All of these previously recorded extinctions have their unique and different extinction reasons, but climate change has a significant role behind all of these outcomes. I like to think of what exactly happens when extinction conditions met to each species or populations. Also, I like to view this as a parasitological perspective. This paper is great.
ReplyDeleteCommenting on Maria's question, I think papers like this are necessary. Acting just for acting because we know it is important won't necessarily make it important to others. But analyses like this help to understand where we stand and how important our actions are, especially to convince people who might not be aware (or even interested) in this kind of things.
ReplyDeleteI personally enjoyed the paper, because for me that was the case: it help me gain a little more perspective on where we currently stand in terms of extinction impacts.
I also think these kind of papers are very important, it shows the scale of the biodiversity crisis we are facing.
ReplyDeleteI had never though of mass extinctions in terms of low origination rates (the authors mention this could have been important in the Devonian and Triassic extinctions). I wonder what would be the effect of anthropogenic activities on origination rate and if in the long term this might have some role in biodiversity dynamics.
In the same vein as Lam's comment, I was also surprised at the sheer amount of extinctions for it to be considered mass extinction. Interesting that it sure seems like we're causing one but technically not yet. I liked comparing the proposed causes in Table 1, it seems like CO2 manipulation is the one factor that links all 5- CO2 is also the factor that we are strongly influencing today. Hmm.
ReplyDeleteResearching to bring light to a potential but under recognized issue is a good focus in a project. I think it’s smart how they were able to point out (somewhat) obvious errors of human kind then back their ideas and views of the world now with data from previous mass extinctions. I like the importance they put on trying to keep the ‘critically endangered’ species alive as well! Not that they are the only way we can avoid mass extinction but that they are important in postponing how soon it happens. Overall, interesting read!
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