In the late 1930s, a small group of guanacos, native South American camelids, was shipped from southern Patagonia to Staats Island, a remote, treeless Falklands island.
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group → ship → Island
Only fifteen animals founded the entire herd.
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animals → found → herd
Roughly twenty-five years later, a cull reduced it from about 300 animals to between 10 and 20.
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cull → reduce → 10
Such a herd would be expected to lose much of its genetic variety.
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herd → expect → variety
Yet scientists who studied the herd more than six decades after its founding found something truly surprising.
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who → study → something
Their analysis showed the island herd still holds genetic diversity comparable to most mainland populations, despite two severe population crashes.
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diversity → show → crashes
Why John Hamilton shipped fifteen guanacos to Staats Island in the late 1930s
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Hamilton → ship → 1930s
According to a 2014 study, ‘
Maintenance of Genetic Diversity in an Introduced Island Population of Guanacos after Seven Decades and Two Severe Demographic Bottlenecks: Implications for Camelid Conservation’ by Benito González, Pablo Orozco-terWengel, Rainer von Borries, Warren Johnson, William Franklin and Juan Marín in the journal PLOS One, guanacos were brought to the Falkland Islands, also known as Islas Malvinas, in the late 1930s by John Hamilton.
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guanacos → accord → Hamilton
He introduced them, together with several other Patagonian species, in an attempt to diversify the local economy.
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He → introduce → economy
The researchers explain that young animals were plausibly captured near Rio Gallegos in Argentina or Pali-Aike in Chile, then shipped to the islands.
Eleven went to Sedge Island and fifteen to Staats Island.
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Eleven → explain → Island
Only the Staats Island animals survived.
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animals → survive → ?
The island covers about 500 hectares at the far western edge of an archipelago of 750 islands, roughly 600 kilometres from the South American coast, and its guanacos have stayed isolated from other populations for more than seventy years.
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guanacos → cover → years
Guanaco sharing a habitat with Magellanic penguins, Punta Tombo (Image: Wikipedia)
How a cull in the late 1950s cut the Staats Island guanaco herd from 300 animals
The herd prospered at first.
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herd → share → animals
According to the study, attempts were later made to eradicate it, to reduce overgrazing and convert the island to sheep farming.
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attempts → accord → farming
This severe culling in the late 1950s drove the population down from 300 animals to its smallest size, between 10 and 20 individuals, in the early 1960s.
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culling → drive → 1960s
The animals were then allowed to recover, with only sporadic, low levels of poaching and culling.
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animals → allow → poaching
By 2004, the herd numbered about 400.
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herd → number → 400
The researchers therefore described a population that had passed through two severe bottlenecks, the founding event and the cull, each time falling below 20 animals.
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that → describe → animals
They expected low genetic diversity as a result.
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They → expect → result
What scientists measured in guanacos from eight localities
To test that expectation, the authors compared the island herd with guanacos from the adjacent mainland and from Tierra del Fuego, using samples from eight localities.
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authors → measure → localities
They studied two kinds of genetic information, variation in the mitochondrial genetic material and variation at microsatellite markers in the nuclear genetic material.
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They → study → material
Six research expeditions visited Staats Island between 1999 and 2008, and the island samples were collected in 2004 and 2005.
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samples → visit → 2004
They came from faeces and carcasses, so no animals had to be captured or handled there.
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animals → come → faeces
The authors also ran computer simulations of the herd's history, using a simulated mainland population of 10,000 animals that was reduced to fifteen.
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that → run → fifteen
They compared the real genetic results with those simulations.
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They → compare → simulations
Guanacos near the La Silla Observatory, 2400 meters above sea level (Image: Wikipedia)
Staats Island guanacos match most mainland herds
The results contradicted the expectation.
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results → match → expectation
The researchers report that the genetic variation on Staats Island was comparable to most mainland populations and greater than that on Tierra del Fuego.
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variation → report → Fuego
The study notes that Tierra del Fuego holds a large population of more than 80,000 guanacos.
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Fuego → note → guanacos
The expected differences in the nuclear markers were not statistically significant between the island herd and the mainland as a whole.
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differences → expect → whole
The authors explain the contrast with Tierra del Fuego by history.
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authors → explain → history
That island's guanacos were isolated thousands of years ago, roughly 8,000 years before the study, so drift has had far longer to act, whereas the Staats Island herd has existed for only about 65 years.
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herd → isolate → years
The mitochondrial markers did show that the island herd had drifted further from the mainland populations than the mainland populations differ from one another.
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populations → show → one
Genetic evidence points to Monte León in southern Patagonia
The study also asked where the founders came from.
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founders → point → where
Of the 23 mitochondrial haplotypes found across all samples, the Staats Island herd carried only three.
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herd → find → three
All three were shared with the Monte León population on the coast of southern Patagonia, the only mainland population that held all of them together.
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that → share → them
The island's most common haplotype appeared on the mainland only at Monte León.
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haplotype → appear → León
Assignment tests supported this.
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tests → support → this
The authors report that 19 of the 20 Staats Island animals tested grouped with the southern Patagonian cluster.
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19 → report → cluster
Monte León lies about 150 kilometres north of Rio Gallegos, the port the animals were shipped from.
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animals → lie → Gallegos
The guanaco population that once lived near Rio Gallegos has since disappeared locally or moved elsewhere.
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that → live → Gallegos
…and 16 more, not listed.
The Aporia
