Extinct megafauna prone to ancient hunger games

14 12 2021

I’m very chuffed today to signal the publication of what I think is one of the most important contributions to the persistent conundrum surrounding the downfall of Australia’s megafauna many tens of millennia ago.

Diprotodon optimum. Artwork by palaeontologist and artist Eleanor (Nellie) Pease (commissioned by the ARC Centre of Excellence for Australian Biodiversity and Heritage)

Sure, I’m obviously biased in that assessment because it’s a paper from our lab and I’m a co-author, but if readers had any inkling of the work that went into this paper, I think they might consider adopting my position. In addition, the injection of some actual ecology into the polemic should be viewed as fresh and exciting.

Having waded into the murky waters of the ‘megafauna debate’ for about a decade now, I’ve become a little sensitive to even a whiff of binary polemic surrounding their disappearance in Australia. Acolytes of the climate-change prophet still beat their drums, screaming for the smoking gun of a spear sticking out of a Diprotodon‘s skull before they even entertain the notion that people might have had something to do with it — but we’ll probably never find one given the antiquity of the event (> 40,000 years ago). On the other side are the blitzkriegers who declaim that human hunting single-handedly wiped out the lot.

Well, as it is for nearly all extinctions, it’s actually much more complicated than that. In the case of Sahul’s megafauna disappearances, both drivers likely contributed, but the degree to which both components played a part depends on where and when you look — Fred Saltré demonstrated that elegantly a few years ago.

Palorchestes. Artwork by palaeontologist and artist Eleanor (Nellie) Pease (commissioned by the ARC Centre of Excellence for Australian Biodiversity and Heritage)

So, why does the polemic persist? In my view, it’s because we have largely depended on the crude comparison of relative dates to draw our conclusions. That is, we look to see if some climate-change proxy shifted in any notable way either before or after an inferred extinction date. If a particular study claims evidence that a shift happened before, then it concludes climate change was the sole driver. If a study presents evidence that a shift happened after, then humans did it. Biases in geochronological inference (e.g., spatial, contamination), incorrect application of climate proxies, poor taxonomic resolution, and not accounting for the Signor-Lipps effect all contribute unnecessarily to the debate because small errors or biases can flip relative chronologies on their head and push conclusions toward uncritical binary outcomes. The ‘debate’ has been almost entirely grounded on this simplistically silly notion.

This all means that the actual ecology has been either ignored or merely made up based on whichever pet notion of the day is being proffered. Sure, there are a few good ecological inferences out there from some damn good modellers and ecologists, but these have all been greatly simplified themselves. This is where our new paper finally takes the ecology part of the problem to the next level.

Led by Global Ecology and CABAH postdoctoral fellow, John Llewelyn, and guided by modelling guru Giovanni Strona at University of Helsinki, the paper Sahul’s megafauna were vulnerable to plant-community changes due to their position in the trophic network has just been published online in Ecography. Co-authors include Kathi Peters, Fred Saltré, and me from Flinders Global Ecology, Matt McDowell and Chris Johnson from UTAS, Daniel Stouffer from University of Canterbury (NZ), and Sara de Visser from University of Groningen (Netherlands).

Read the rest of this entry »

Extinction cascades

3 06 2020

A recent online interview I did on the role of extinction cascades in mass extinctions:

Global warming causes the worst kind of extinction domino effect

25 11 2018

Dominos_Rough1-500x303Just under two weeks ago, Giovanni Strona and I published a paper in Scientific Reports on measuring the co-extinction effect from climate change. What we found even made me — an acknowledged pessimist — stumble in shock and incredulity.

But a bit of back story is necessary before I launch into describing what we discovered.

Last year, some Oxbridge astrophysicists (David Sloan and colleagues) published a rather sensational paper in Scientific Reports claiming that life on Earth would likely survive in the face of cataclysmic astrophysical events, such as asteroid impacts, supernovae, or gamma-ray bursts. This rather extraordinary conclusion was based primarily on the remarkable physiological adaptations and tolerances to extreme conditions displayed by tardigrades— those gloriously cute, but tiny (most are around 0.5 mm long as adults) ‘water bears’ or ‘moss piglets’ — could you get any cuter names?


Found almost everywhere and always (the first fossils of them date back to the early Cambrian over half a billion years ago), these wonderful little creatures are some of the toughest metazoans (multicellular animals) on the planet. Only a few types of extremophile bacteria are tougher.

So, boil, fry or freeze the Earth, and you’ll still have tardigrades around, concluded Sloan and colleagues.

When Giovanni first read this, and then passed the paper along to me for comment, our knee-jerk reaction as ecologists was a resounding ‘bullshit!’. Even neophyte ecologists know intuitively that because species are all interconnected in vast networks linked by trophic (who eats whom), competitive, and other ecological functions (known collectively as ‘multiplex networks’), they cannot be singled out using mere thermal tolerances to predict the probability of annihilation. Read the rest of this entry »

Rich and stable communities most vulnerable to change

16 08 2016

networkI’ve just read an interesting new study that was sent to me by the lead author, Giovanni Strona. Published the other day in Nature Communications, Strona & Lafferty’s article entitled Environmental change makes robust ecological networks fragile describes how ecological communities (≈ networks) become more susceptible to rapid environmental changes depending on how long they’ve had to evolve and develop under stable conditions.

Using the Avida Digital Evolution Platform (a free, open-source scientific software platform for doing virtual experiments with self-replicating and evolving computer programs), they programmed evolving host-parasite pairs in a virtual community to examine how co-extinction rate (i.e., extinctions arising in dependent species — in this case, parasites living off of hosts) varied as a function of the complexity of the interactions between species.

Starting from a single ancestor digital organism, the authors let evolve several artificial life communities for hundred thousands generation under different, stable environmental settings. Such communities included both free-living digital organisms and ‘parasite’ programs capable of stealing their hosts’ memory. Throughout generations, both hosts and parasites diversified, and their interactions became more complex. Read the rest of this entry »

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