Cleaning up the rubbish: Australian megafauna extinctions

15 11 2013

diprotodonA few weeks ago I wrote a post about how to run the perfect scientific workshop, which most of you thought was a good set of tips (bizarrely, one person was quite upset with the message; I saved him the embarrassment of looking stupid online and refrained from publishing his comment).

As I mentioned at the end of post, the stimulus for the topic was a particularly wonderful workshop 12 of us attended at beautiful Linnaeus Estate on the northern coast of New South Wales (see Point 5 in the ‘workshop tips’ post).

But why did a group of ecological modellers (me, Barry Brook, Salvador Herrando-Pérez, Fréd Saltré, Chris Johnson, Nick Beeton), ancient DNA specialists (Alan Cooper), palaeontologists (Gav Prideaux), fossil dating specialists (Dizzy Gillespie, Bert Roberts, Zenobia Jacobs) and palaeo-climatologists (Michael Bird, Chris Turney [in absentia]) get together in the first place? Hint: it wasn’t just the for the beautiful beach and good wine.

I hate to say it – mainly because it deserves as little attention as possible – but the main reason is that we needed to clean up a bit of rubbish. The rubbish in question being the latest bit of excrescence growing on that accumulating heap produced by a certain team of palaeontologists promulgating their ‘it’s all about the climate or nothing’ broken record.

I’m talking about that so-called ‘debate’ about megafaunal extinctions: the ‘it’s all humans’ versus ‘it’s all climate change’ polemic that has stymied palaeo-ecological progress in Australia and elsewhere for decades.

One of the main reasons the polemic has persisted – particularly in Australia – is that the foundational data on which pet hypotheses rest are so full of holes and rotting timbers that any scientific structure built upon it is shaky to say the least.

Why (and again, focussing particularly on Australia here)? It mainly comes down the number and quality of dated fossil specimens (and associated material) from which extinction timelines can be inferred. In our response to the aforementioned excrescence, we highlighted many of these problems, including insufficient numbers of dated specimens from which extinction times can be inferred (believe it or not, the ‘climate champions’ actually took single [or two] dates to infer an extinction time!), no accounting for the Signor-Lipps effect (incomplete records likely missing actual extinction times) and utterly useless dates derived from archaic, supplanted, too-imprecise or inconsistent methods.

I’m not suggesting that all the available data are utterly useless, but one has to be very, very careful about how they are used. So one of our main tasks at Linnaeus was to pour over all the best-quality time series and develop a set of objective criteria for rating the validity of each date. Next, we started a process of modelling to account for things like Signor-Lipps and Lazarus (assuming extinction occurred at the terminal date, when in fact it could have easily persisted past this time) effects (see our work the GRIWM as an example). Finally, we started pulling together the best palaeo-climate data for Australia, and seriously challenging the broad-brush use of inappropriate climate proxies that have plagued Quaternary studies in Australia for quite some time.

Of course, one cannot create better data (although we can refine dates and ultimately collect more specimens), so there are limitations to relying solely on fossil records. That is why other lines of evidence are also required. We have been involved in several of these over the last few years, including incorporating data on clade shifts from ancient DNA, using indices of dung fungus spores to indicate the relative abundance of now-extinct fauna, reworking archaeological data, statistical approaches and modelling the likelihood of certain phenomena from well-established ecological first principles (see here and here).

We are using all of these approaches and available information to redefine how we understand pre-historic extinctions. So stay tuned for some high-level outputs originating from this workshop (and others in the near future) and easily one of the best teams I’ve worked with in years. Thanks to Dizzy, Bert, Zenobia, Barry, Salva, Fréd, Michael, Nick, Chris, Chris, Gav, Alan and our newest database manager, Marta. I also thank my team at The Environment Institute and the great people at Linnaeus for a wonderfully smooth and convivial experience. As such, I’m excited about the future of palaeo-ecology in Australia!

CJA Bradshaw


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4 12 2013
Biowealth: all creatures great and small | ConservationBytes.com

[…] at sparrow’s on Monday, then drove a hire car down to The ‘Gong to follow up on some Australian megafauna databasing & writing with Bert Roberts & Zenobia Jacobs. On Tuesday morning we then flitted over to Canberra where […]

18 12 2013
Rubenature

Reblogged this on 4thenature'sake and commented:
A month ago I published this post: http://4thenaturesake.wordpress.com/2013/11/04/climate-change-not-human-activity-led-to-megafauna-extinction/ about how climate change drove megafauna to extinction and not the human activity.
There is now an excellent reply to this idea. Hope you will enjoy as much as me with this debate.

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