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Iguanas invade island
Not directly topical but of general interest. From today's New York
Times Online, distributed for "Fair Use" purposes only.
Presumably this kind of inadvertant colonialism could not have
happened with dinosaurs, right? An active metabolism and general
large size would presumably preclude dinosaur journeys of this kind....
* * *
Iguanas Sail From Guadeloupe to Anguilla and Into History
By CAROL KAESUK YOON
Fifteen iguanas on a tangle of waterlogged trees, tossed into the
Caribbean Sea by a hurricane, have apparently sailed 200 miles from
Guadeloupe to Anguilla and into biological history, scientists say.
Their report, being published Thursday in the journal Nature, has
amazed scientists, who have been arguing since early this century
about whether such journeys were even remotely possible, let alone
By documenting the 1995 voyage of the 15 large, land-loving creatures
-- enough to form a new population -- the report provides the first
clear-cut evidence in support of biologists who argue that seemingly
impossible journeys like this could have been an be important avenue
for the dispersal of species around the world.
"It was a major invasion," said Dr. Ellen Censky, a reptile expert who
has worked on Anguilla and was the lead author of the paper.
"I got a phone call saying iguanas had come onto the island," said Dr.
Censky, now director of the Connecticut State Museum of Natural
History at the University of Connecticut. "My first thought was that
that couldn't have happened. Then somebody sent a snapshot. I thought,
'My God, 'that's it, that's it."'
Dr. James Brown, ecologist and biogeographer at the University of New
Mexico, said: "It's a spectacular observation. Some of the things
nature can do are pretty incredible."
The journey of the iguanas began in September 1995 when two powerful
hurricanes moved through the eastern Caribbean. A month later the
iguanas, fearsome-looking creatures up to 4 feet long that resemble
dinosaurs, washed up on Anguilla's shores on an immense raft of trees,
the Nature paper reported.
Dr. Censky said the lizards, which rest in trees, were probably blown
down with them into the sea. She and her colleagues studied the tracks
of the two hurricanes, Luis and Marilyn, and ocean currents and
decided that the lizards probably came from Guadeloupe.
"I was completely surprised to see iguanas coming," Cleve Webster, a
fisherman on Anguilla, said in a telephone interview.
Webster, who witnessed the invasion with his brother while they were
checking lobster traps, said, "One iguana, he was on a log and the
length of his tail was hanging over into the water."
Dr. Censky, along with Dr. Judy Dudley, a U.N. volunteer in Anguilla,
and Karim Hodge, an employee with the Anguilla National Trust,
interviewed eyewitnesses to the iguana landing and then tracked and
monitored the iguanas as they dispersed. Dr. Censky said they were
able to verify 15 animals, but suspected there were more. Identifying
the lizards, known as green iguanas, as outsiders was simple,
researchers said. They have a blue-green coloration and dark rings
around their tails, making them easily distinguishable from the other
iguana species on the island, which is brown and has a plain tail.
Though the arriving iguanas appear to have been weak, dehydrated and,
in some cases, injured, a number survived. In March, researchers said
they found what appeared to be a pregnant female iguana, the last
element of a successful colonization of a new species, which made the
observation of the rafting significant. Because the animals appear to
be reproducing, the researchers said they believed the new arrivals
had established themselves, though other scientists said it was still
too soon to tell.
While some Anguillans are concerned about the possible ecological
impact of the new lizards on the island, Dr. Censky said she was not
because their arrival and any changes brought by them would be
The new study bolsters the claims of those, like Dr. Blair Hedges, an
evolutionary biologist at Pennsylvania State University, who have been
advocating this type of rafting as a major explanation for the
distribution of animals on islands in the Caribbean and elsewhere.
Isolated ocean islands like the Hawaiian islands would be devoid of
terrestrial animals were it not for rafting, or the transportation of
species by people.
"In my mind, it's not unexpected," Hedges said. "If we can see green
iguanas land on Anguilla in 1998, just think of all the storms in all
the millions of years and there is a real probability of getting
anywhere in the world."
Other researchers, like Ross MacPhee, curator of mammalogy at the
American Museum of Natural History, while acknowledging that rafting
clearly can occur, were not sold on its wholesale importance. MacPhee
said he still thought ancient land bridges, stretches of land long
since disappeared that are hypothesized to have connected islands in
the Caribbean to South America, were likely to be a much more
important mechanism for getting animals to islands.
MacPhee said land bridges were particularly important for mammals that
did not tolerate starvation or dehydration as well as reptiles.
"We don't have to infer little drowned rats hanging desperately on to
tree trunks," he said, "to explain why the faunas look the way they
In fact, rafting is just one of a number of seemingly outlandish
mechanisms, which researchers have had to infer to explain how
different creatures have arrived where they are today. Among the
harder-to-believe explanations have been geologically implausible land
bridges or the suggestion that fish might have been swept up in
tornadoes and moved across land to establish themselves in other
bodies of water.
Rafting, for some, was equally hard to believe until now. While there
have been many records of single, usually small, animals drifting
about the ocean, it takes two to set up a new population (unless one
is a pregnant female).
Dr. Censky said, however, that the only previous evidence that
multiple animals might have rafted together was a 30-year-old paper
documenting three toads found floating on a log in the middle of a
lake. "It wasn't even over-the-sea rafting," Dr. Censky said.
But in biogeography, a field that by its very nature seems to invite
wild speculation, the seemingly wild explanations are often confirmed,
as in the report Thursday. Years ago, the suggestion that some species
are where they are because the continents themselves moved was met
with the most intense ridicule. Today it is dogma, leaving the
theory's early proponents with the last laugh. Researchers advice?
Expected the unexpected.
"Over the long term," said Brown of the University of New Mexico,
"improbable events become highly likely. Not everything is going to
get everywhere, but things will definitely end up in surprising
* * *
"There are times when verbal ingenuity is not enough."
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