Barnosky et al. 2011 - by R. Kiat

Barnosky et al. 2011

Barnosky, A. D., Matzke, N., Tomiya, S., Wogan, G. O., Swartz, B., Quental, T. B., ... & Mersey, B. (2011). Has the Earth/'s sixth mass extinction already arrived?. Nature, 471(7336), 51-57.

blog by Rebecca Kiat

Paper Authors (Full list):

Anthony D. Barnosky, Nicholas Matzke, Susumu Tomiya, Guinevere O. U. Wogan, Brian Swartz, Tiago B. Quental, Charles Marshall, Jenny L. McGuire, Emily L. Lindsey, Kaitlin C. Maguire, Ben Mersey & Elizabeth A. Ferrer.

First three authors (info from personal websites):

Anthony D. Barnosky:

“Research revolves around calibrating past planetary changes and what they mean for understanding today’s global change. Current projects focus on the extinction crisis, climate change, the Anthropocene, and conservation biology, with the goal of understanding the state of the planet today and how we can guide it toward a future we want, rather than one that inadvertently happens to us.”

Nicholas Matzke:

“Biogeography is the study of where species live, and why. Traditionally, the "why" has been divided into "Ecological Biogeography" and "Historical Biogeography." Ecological Biogeography has focused on environmental and ecological controls on distribution, such as temperature and precipitation.  "Historical Biogeography" has focused on how geographic ranges evolve on geological timescales and across phylogenetic trees, primarily dealing with rare dispersal and vicariance events.

I believe that it is high time that these two traditions were re-integrated, not just in verbal models and interpretation, but with formal probabilistic models, using the computational tools of statistical phylogenetics. My work focuses on building these tools, and using them to answer Big Questions in evolution and biogeography.”

Susumu Tomiya:

"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."

Press release in ScienceDaily:

https://www.sciencedaily.com/releases/2011/03/110302131844.htm

Paper Summary:

Barnosky et al. 2011 is a review paper that seeks to address the question: “Has the Earth’s sixth mass extinction already arrived?”.

“Thus, mass extinction, in the conservative paleontological sense, is when extinction rates accelerate relative to origination rates such that over 75% of species disappear within a geologically short interval—typically less than 2 million years, in some cases much less…”

The big five extinction events were distinct in having spiked levels of extinction rates (a decrease in origination rates for Devonian and Triassic events has also been suggested) compared to background extinction rates and in their magnitude (with over ~75% if species estimated to have been loss). It has been already suggested that humans might be driving a sixth mass extinction via e.g. fragmenting habitats, introducing non-native species, changing global climate etc.

In this paper, Barnosky et al. synthesize previous knowledge as well as the many issues and disparities in data and in analysis in attempting to answer this question using fossil data and modern data in order to evaluate comparative extinction rates accurately. For example, certain taxa, such bivalves, are better preserved and dominate the fossil record, but these species are poorly assessed or under-sampled today. Analyses of fossils are often done at genus level where similar morphologies are grouped together even if they may be distinct, while modern taxa are analyzed at the level of species. Extinction rates can also vary dramatically based upon the length of time measured – using a short time frame could yield a rate that is markedly faster or slower than the long-term average million-year rates. Barnosky et al. address these concerns and others in this paper (Box 1), along with possible comparative techniques that could help address these issues.

For their own approach, Barnosky et al. used a conservative approach in assessing extinction rates and in their comparisons (Table 2 for specifics). They found that recent extinctions according to their conservative analysis do not qualify (as of yet) for a mass extinction if using Big Five as a benchmark for a mass extinction (Fig 1. For comparative extinction rates depending on time intervals and Fig. 2 for comparative extinction magnitude). However, if species currently in the ‘threatened’ or in the ‘critically endangered’ categories as evaluated by IUCN went extinct within the next century and extinction rates remain the same, the sixth extinction event could be underway (Figure 3 – hypothetical; if extinction events were scaled to a length of 500 years).

Questions:

I was curious about current origination rates. If more recent research suggest that the Devonian and Triassic events were more a result of a decrease in origination rates, how is it taken into account here? (Note: This is mentioned in the notes for Table 2: diversification rates)