World's Smallest Gecko/ Lizard.... Discovered....on Hispaniola....
- Tiny Lizard Illustrates Big Lessons on Habitat
By Guy Gugliotta
Washington Post Staff Writer
Monday, December 3, 2001; Page A09
The world's smallest reptile can sit on a dime and lives on a tiny,
scrub-covered Caribbean island that larger predatory species -- including
humans -- either couldn't find or didn't want.
This little gecko lizard, Sphaerodactylus ariasae, suggests that good
things come in small packages. The Caribbean islands, together about the
size of Oregon, are also home to the Lesser Antillean threadsnake and the
bee hummingbird -- the world's smallest snake and bird, and the Cuban
coqui, the smallest frog in North America.
Islands have been renowned for unique ecosystems since Charles Darwin
visited the Galapagos, but they also provide lessons in the intricate
relationship between habitat and the ability of animals, both large and
small, to survive amid humankind's intrusions.
"Islands get colonized by species that float over on logs or get carried in
a bird's feathers," said biologist Blair Hedges of Pennsylvania State
University. "Some groups never make it, but the groups that do, have more
room to spread out. They don't have competition."
Hedges and University of Puerto Rico biologist Richard Thomas found the
tiny gecko in "leaf litter" surrounding a limestone sinkhole on Isla Beata,
a 16.3-square-mile islet off the Dominican Republic. Their findings, which
are being announced today, are reported in the December issue of the
Caribbean Journal of Science.
The gecko is dark brown, measures six-tenths of an inch and is easily
recognizable as a lizard. "You have to get down on your hands and knees and
root through the forest floor to look for a sudden movement," Hedges said.
"They're very dark and very fast."
Hedges said he and Thomas found eight lizards on Isla Beata and in nearby
Jaragua National Park, on the Dominican mainland, but traces soon vanished
as the searchers moved inland.
"It's a national park, but there are people living there," Hedges said.
"They have to eat, so they cut trees to plant cassava and beans, and to
make charcoal. One family can wipe out acres and acres."
Because of dangers like these, ecologists regard the Caribbean as one of 25
threatened biodiversity "hot spots," areas making up only 1.4 percent of
the Earth's surface but where 44 percent of all plant species and 35
percent of all vertebrate land species can be found.
Besides the Caribbean, hot spots include the islands of Sri Lanka,
Polynesia-Micronesia, Madagascar, New Zealand, Indonesia and the
Philippines. They also include mainland sites such as Panama's Darien Gap,
the Mediterranean coast (including all of Italy and Greece) and the Burmese
Threats can be deliberate -- from poachers or slash-and-burn farmers -- but
can also come from almost incidental human encroachments on fragile
habitat. "The areas that survive are the areas farthest away from roads,"
Yet species endure in the Caribbean, even though only about 10 percent of
the region's virgin forest remains. Isla Beata has a long history as a
pre-Columbian indigenous settlement, a colonial-era pirate hideout, a salt
mine that closed in 1960 and a campsite for today's local fishermen.
Scientists are quick to point out that the isolation of island living does
not ensure species prosperity. "It may be true that as we create an island
world, we may create new species," said Columbia University biologist
Stuart L. Pimm, an expert in species extinction and survival. "But we may
have to wait a few million years for them to evolve."
Also, "islandizing" mainland habitat by accidentally framing chunks of
wilderness with highways or hedgerows is not likely to preserve
biodiversity. "Water is not a threat to a real island," Pimm said. "But as
we create forest fragments, the areas around them become weedy, invasive
and bring in bad species."
Tiny animals like Hedges's gecko may be able to survive in shrinking
habitat, but large animals suffer. "On average, big species become extinct
a lot faster than small species," Pimm said.
This phenomenon -- that bigger species need bigger land masses to survive
-- is the theme of a new study describing the largest land vertebrates at
25 oceanic locations and five continents over the last 65,000 years.
The study, published last week in the Proceedings of the National Academy
of Sciences, found that animal species grew bigger on larger land masses,
that plant-eaters were approximately 10 times as big as carnivores in the
same area, and that cold-blooded animals, with lower metabolism, were much
bigger than warm-blooded creatures, who needed more to eat.
The study examined habitats ranging from the 29-acre Galapagos islet of
Plaza Sur, where the six-pound Galapagos land iguana is king, to the 21
million-square-mile Eurasian land mass, home of the now-extinct,
12,000-pound woolly mammoth.
"Roughly it takes between a thousand [individuals] or a few thousand of
anything to survive," said Jared Diamond, a UCLA Medical School
physiologist and the study's co-author.
Since land requirements are greater for big animals, those are "the most
threatened, because they evolved to occupy the full size of their habitat."
Humans, increasingly, are filling their space.
Diamond said he and his co-authors chose 65,000 years as the study's cutoff
point because that is when modern humans reached Australia. The largest
species on this biggest of islands were marsupials, mammals who nurse
offspring in an external pouch, and the biggest was the 2,500-pound
diprotodon. By 40,000 years ago, however, it had been hunted to extinction.
The biggest marsupial in Australia today is the 190-pound red kangaroo.
A similar fate befell the giants of the Americas after humans crossed the
land bridge from Asia between 13,000 and 20,000 years ago. The Columbian
mammoth, at 13,000 pounds, the sabretooth tiger, at 860 pounds, and the
950-pound American lion are all extinct.
By contrast, today's African lion and elephant, considerably smaller than
their departed American cousins, are still the biggest animals that
continent ever produced over the last 65,000 years. They survive, Diamond
suggested, because they watched modern humans evolve over several million
"Animals had a chance to get more suspicious as humans got more
sophisticated," Diamond said. "Unfortunately for the mammoths, mastodons
and sloths in America, the first humans they encountered were professional