When devils and thylacines went extinct

17 01 2018

devil-thylacine-extinctWe’ve just published an analysis of new radiocarbon dates showing that thylacines (Tasmanian ‘tigers’, Thylacinus cynocephalus) and Tasmanian devils (Sarcophilus harrisi) went extinct on the Australian mainland at the same time — some 3200 years ago.

For many years, we’ve been uncertain about when thylacines and devils went extinct in mainland Australia (of course, devils are still in Tasmania, and thylacines went extinct there in the 1930s) — a recent age for the devil extinction (500 years before present) has recently been shown to be unreliable. The next youngest reliable devil fossil is 25000 years old.

So, knowing when both species went extinct is essential to be able to determine the drivers of these extinctions, and why they survived in Tasmania. If the two extinctions on the mainland happened at the same time, this would support the hypothesis that a common driver (or set of drivers) caused both species to go extinct. Read the rest of this entry »

Don’t blame it on the dingo

21 08 2013

dingo angelOur postdoc, Tom Prowse, has just had one of the slickest set of reviews I’ve ever seen, followed by a quick acceptance of what I think is a pretty sexy paper. Earlier this year his paper in Journal of Animal Ecology showed that thylacine (the badly named ‘Tasmanian tiger‘) was most likely not the victim of some unobserved mystery disease, but instead succumbed to what many large predators have/will: human beings. His latest effort now online in Ecology shows that the thylacine and devil extinctions on the Australian mainland were similarly the result of humans and not the scapegoat dingo. But I’ll let him explain:

‘Regime shifts’ can occur in ecosystems when sometimes even a single component is added or changed. Such additions, of say a new predator, or changes such as a rise in temperature, can fundamentally alter core ecosystem functions and processes, causing the ecosystem to switch to some alternative stable state.

Some of the most striking examples of ecological regime shifts are the mass extinctions of large mammals (‘megafauna’) during human prehistory. In Australia, human arrival and subsequent hunting pressure is implicated in the rapid extinction of about 50 mammal species by around 45 thousand years ago. The ensuing alternative stable state was comprised of a reduced diversity of predators, dominated by humans and two native marsupial predators ‑ the thylacine (also known as the marsupial ‘tiger’ or ‘wolf’) and the devil (which is now restricted to Tasmania and threatened by a debilitating, infectious cancer).

Both thylacines and devils lasted on mainland Australia for over 40 thousand years following the arrival of humans. However, a second regime shift resulted in the extinction of both these predators by about 3 thousand years ago, which was coincidentally just after dingoes were introduced to Australia. Dingoes are descended from early domestic dogs and were introduced to northern Australia from Asia by ancient traders approximately 4 thousand years ago. Today, they are Australia’s only top predator remaining, other than invasive European foxes and feral cats. Since the earliest days of European settlement, dingoes have been persecuted because they prey on livestock. During the 1880s, 5614 km of ‘dingo fence’ was constructed to protect south-east Australia’s grazing rangelands from dingo incursions. The fence is maintained to this day, and dingoes are poisoned and shot both inside and outside this barrier, despite mounting evidence that these predators play a key role in maintaining native ecosystems, largely by suppressing invasive predators.

Perhaps because the public perception of dingoes as ‘sheep-killers’ is so firmly entrenched, it has been commonly assumed that dingoes killed off the thylacines and devils on mainland Australia. People who support this view also point out that thylacines and devils persisted on the island of Tasmania, which was never colonised by dingoes (although thylacines went extinct there too in the early 1900s). To date, most discussion of the mainland thylacine and devil extinctions has focused on the possibility that dingoes disrupted the system by ‘exploitation competition’ (eating the same prey), ‘interference competition’ (wasting the native predators’ precious munching time), as well as ‘direct predation’ (dingoes actually eating devils and thylacines). Read the rest of this entry »

Science immortalised in cartoon

1 02 2013

Well, this is a first for me (us).

I’ve never had a paper of ours turned into a cartoon. The illustrious and brilliant ‘First Dog on the Moon‘ (a.k.a. Andrew Marlton) who is chief cartoonist for Australia’s irreverent ‘Crikey‘ online news magazine just parodied our Journal of Animal Ecology paper No need for disease: testing extinction hypotheses for the thylacine using multispecies metamodels that I wrote about a last month here on ConservationBytes.com.

Needless to say, I’m chuffed as a chuffed thing.



No need for disease

7 01 2013

dead or alive thylacineIt’s human nature to abhor admitting an error, and I’d wager that it’s even harder for the average person (psycho- and sociopaths perhaps excepted) to admit being a bastard responsible for the demise of someone, or something else. Examples abound. Think of much of society’s unwillingness to accept responsibility for global climate disruption (how could my trips to work and occasional holiday flight be killing people on the other side of the planet?). Or, how about fishers refusing to believe that they could be responsible for reductions in fish stocks? After all, killing fish couldn’t possibly …er, kill fish? Another one is that bastion of reverse racism maintaining that ancient or traditionally living peoples (‘noble savages’) could never have wiped out other species.

If you’re a rational person driven by evidence rather than hearsay, vested interest or faith, then the above examples probably sound ridiculous. But rest assured, millions of people adhere to these points of view because of the phenomenon mentioned in the first sentence above. With this background then, I introduce a paper that’s almost available online (i.e., we have the DOI, but the online version is yet to appear). Produced by our extremely clever post-doc, Tom Prowse, the paper is entitled: No need for disease: testing extinction hypotheses for the thylacine using multispecies metamodels, and will soon appear in Journal of Animal Ecology.

Of course, I am biased being a co-author, but I think this paper really demonstrates the amazing power of retrospective multi-species systems modelling to provide insight into phenomena that are impossible to test empirically – i.e., questions of prehistoric (and in some cases, even data-poor historic) ecological change. The megafauna die-off controversy is one we’ve covered before here on ConservationBytes.com, and this is a related issue with respect to a charismatic extinction in Australia’s recent history – the loss of the Tasmanian thylacine (‘tiger’, ‘wolf’ or whatever inappropriate eutherian epithet one unfortunately chooses to apply). Read the rest of this entry »

Ghost extinctions

5 07 2012

The Philippine bare-backed fruit bat (Dobsonia chapmani; body size = < 220 mm, < 150 g; IUCN status: ‘Critically Endangered A2cd’) is endemic to lowland rain forests [top habitat image] from Negros and Cebu islands. This species of flying fox had been missing from the 1970s and was declared extinct in 2002 (34). In May 2003, five specimens [one shown in the picture above] were trapped in night nets in the Calatong forest (Negros Island), a ~ 1,000-ha fragment of secondary rain forest and agricultural lands [bottom habitat image] (35). The species is reliant on fruit-bearing vegetation and caves for feeding and roosting, respectively. As with many other Philippine bats, it suffers from habitat degradation and hunting. The family Pteropodidae comprises > 150 species. Despite their Draculian look, they all feed on fruits and nectar, and act as important plant pollinators (36), as well as disease vectors such as Ebola virus (37). Flying foxes are distributed in the tropics and subtropics from the Eastern Mediterranean, through the Arabian Peninsula, Asia, Australia, and many islands of the Indian Ocean. Photos courtesy of Ely L. Alcala.

Jared Diamond (1) coined the expression ‘evil quartet’ for the four main human causes of species extinctions: habitat loss/fragmentation, overkill, introduced species and extinction chains [with climate change and extinction synergies (2), the updated expression would be ‘evil sextet”]. However, one third of ‘extinct’ mammal species has been ‘found’ again. Recent studies reveal that the probability of rediscovery depends on the cause of extinction.

Arriving in a city to search for an old friend, I would first look in the suburb where he lived, the pub where we enjoyed a drink and some music, or the park where we used to play football. But if my friend was an outlaw, or had recently gone through a traumatic experience, my chances of finding him at his favourite spots would shrink.

If, instead of a friend, we are searching for the last survivors of an extinct-declared species, surveys also tend to take place in the habitat in which the species was previously found. Such a strategy rests on the classical hypothesis that, given the spatial distribution of a species, its gradual decline must occur from the periphery to the core of its distribution (‘range collapse’) where, in theory, the habitat should be of better quality and the number of individuals higher (3). In contrast, recent work supports that the trajectory of demise of threatened vertebrates progresses from the core to the periphery (‘range eclipse’) (4), because many perturbations make their way as a progressive wave, e.g, fire, logging or urbanisation.

Diana Fisher (5) supports the ‘range eclipse’ hypothesis for ‘extinct’ mammals which have been rediscovered. She quantifies that 60% of the new records are made from peripheral habitats, mainly when the principal cause of extirpation is habitat loss. Not only that, on average species are rediscovered at altitudes 35 % higher than historical records, and only in 5 % of the cases at the locality where it had been last seen.

Read the rest of this entry »