Life lines

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© The Ecological Society of America







Staving off extinction


xtinction is the rule. Survival is the exception.” Carl  

 Sagan’s premonitory words are vindicated by the 

 oft- heard statistic that over 99% of all species that ever 

lived are now extinct. But while his message is clear, it 

might be said to contain a tiny technical flaw, since no 

 species ever became extinct that did not first survive. The 

true exception is not survival, but continued survival

 something that requires a species to show ongoing pluck 

while enjoying continual and timely good luck. Any 

Bramble Cay melomys (Melomys rubicola; WebFig ure 1) or 

Lord Howe Island stick insect (Dryococelus australis) – two 

species that until recently were found only on one small 

oceanic island each – could tell you that.

Bramble Cay is a flat, Australian island in the Torres 

Strait, some 227 km north of Queensland’s Cape York 

Peninsula. It’s tiny: just over 300 m long by 100 m wide, 

less than half of it (an area the size of a soccer field) with 

any vegetation, all low- 

lying. Yet this speck of land, 

where the only fresh water 

is what falls as rain, has 

been home to generations 

of its eponymous melomys. 

In fact, the population of 

these 100- g rodents is esti-

mated to have run, at times, 

into the hundreds (Aust 

Mammal 1983; 6: 77–79). 

How the species appeared 

on the island is a mystery, 

but that it survived and 

prospered is all but a mira-

cle. If ever there was a 

mammal with uncommon 

pluck (read adaptability and tenacity) and incredible luck 

(while it lasted), surely it was this.

A miniscule island, however, is no place to be when 

your luck runs out. Though Bramble Cay is among the 

first places in the world to welcome the New Year, there 

will be no 2017 for its melomys. A June 2016 report to the 

Queensland Government’s Department of Environment 

and Heritage Protection ( records 

not a single specimen captured during a 2014 survey. The 

report’s authors suggest the species to be the first mamma-

lian taxon lost primarily to human- caused climate change

a victim of rising sea levels and more aggressive weather 

salt- lashing the vegetation on which it depended. Maybe. 

But were it not for luck, anything from genetic drift during 

lean times to a few extra days of drought or high ocean 

swell (the island’s maximum elevation is just 3 m) could 

have wiped it out well before now. The authors recom-

mended the species’ status be changed from “endangered” 

to “extinct” in Australia, but only suggested that “possibly 

extinct” be added to its “critically endangered” rating on 

the IUCN Red List – and the Lord 

Howe Island stick insect knows why.

Back in the 1920s, these hand- long 

arthropods were extirpated from their 

home on Lord Howe Island, off Australia’s eastern coast, by, 

ironically, an invasion of the Bramble Cay melomys’ cousin, 

the black rat (Rattus rattus). Descendants of animals that 

jumped ship from the British steamer SS Makambo, which ran 

aground on the island in 1918, the intruders set to work, dec-

imating the stick insects which they found an appealing

crunchy snack. This stroke of rotten luck, it was believed, had 

driven the species to extin ction. But 20 km away, on another 

tiny island (1100 m × 300 m), luck of a different kind was 

holding. Ball’s Pyramid (WebFig ure 2), an almost bare vol-

canic stack reaching over 560 m into the air, could not be 

more different from Bramble Cay. Nor could the fate of the 

few stick insects that somehow got there differ more greatly 

from that of the Bramble 

Cay melomys. In 1964, 

climbers tantalizingly found 

dead specimens on the 

island. Then, in February 

2001, on a rock terrace 65 

m above the waves, resear-

chers discovered two adults 

and a nymph clinging to  

life under a small shrub 

(Melaleuca howeana) (Bio­

divers Conserv 2003; 12

1391–403). Plant debris at 

the base of the shrub 

retained water from a seep, 

and provided their refuge. A 

year later, others were 

found: 24 in all. Like the melomys, no one knows how they 

reached the island. Like the melomys, they lived in precari-

ous isolation. Like the melomys, their survival depended on 

being plucky. But unlike the melomys, they had not stopped 

being lucky. And their luck has since burgeoned; a program 

run by the Melbourne Zoo has bred thousands of them from a 

single pair, aptly named Adam and Eve (

watch?v=Eg3dcYJ2oI4). It is even hoped that one day Lord 

Howe Island may be successfully repopulated. No such luck 

for the Bramble Cay melomys.

Or maybe there is. Maybe out there on some small 

island off Papua New Guinea, perhaps a little higher than 

Bramble Cay and with just enough rain and vegetation, a 

few melo myses are awaiting their rediscovery. I wonder 

what New Year’s advice on continued survival they might 

give us, a species pushing its luck, yet living on an island 

floating in space.

Lord Howe Island stick insect (Dryococelus australis).

Granitehighs; license: CC BY



Adrian Burton

(     @AdrianBurton_)

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