John Pickrell
for National Geographic News
October 10, 2002
An ecological treasure trove of brightly colored and diverse
new frog species has been discovered on the tea-plantation-covered
island of Sri Lanka. The discovery of more than a hundred
new rain-forest species makes the country a new center of
frog diversity and increases the urgency for protecting what
little forest it retains.
The new finding increases the island's previously known
tree frog diversity more than fivefold to over 100 species.
Sri Lanka's status as an amphibian biodiversity hotspot now
challenges that of other tropical islands, including Borneo,
Madagascar, and New Guinea which are ten times or more as
large, yet have similar numbers of frog species.
"The simultaneous discovery of more than 100 species
is…astonishing news," said David Skelly of Yale
University's School of Forestry and Environmental Studies
in New Haven, Connecticut. "Sri Lanka is relatively small
and relatively well known compared to much of the tropics,"
he said. The discovery "is testimony to how little we
know about the distribution of biodiversity."
Five of the new species are tree frogs that lay eggs in homespun
foam baskets suspended above water—from whence the tadpoles
take their first dip. The remainder are all species that produce
young on the forest floor in robust eggs. These direct-developing
young avoid being tadpoles and emerge as fully fledged, if
tiny, versions of their parents.
The new species have a variety of remarkable body forms,
said Christopher J. Schneider, a biologist at Boston University.
These species run the gamut from tiny leaf-litter dwellers
to large tree-living types. Some live on rocks and have leg
fringes and markings that help disguise them as clumps of
moss, he said.
Global Free Fall
The discovery is good news considering the recently documented
declines in amphibian numbers worldwide. "The discovery
of these species is just an indication that we are losing
some of the world's most important resources before we even
know what those resources really are," said John W. Wilkinson,
International Coordinator for the Declining Amphibian Populations
Task Force at the Open University in Milton Keynes, England.
Around 5,000 amphibian species, including frogs, toads, newts,
and salamanders are thought to exist today. These often semi-aquatic
animals live in environments ranging from wetlands and forests
to savannas and deserts.
Since the 1950s many species of amphibians have experienced
plummeting numbers associated with habitat loss and other
adverse human activities. However, since the late 1980s biologists
began reporting an escalation in these declines worldwide—often
with no clear cause, and even severely affecting species in
otherwise pristine habitats such as national parks and nature
reserves.
Scientists have been at a loss to find a single factor responsible
for the declines that have caused the extinction of many species.
Possible causes include pollutants such as pesticides, diseases
such as fungal infections, climate change, and more ultraviolet
radiation due to thinning ozone layers.
Declining amphibian populations are a concern, said Wilkinson,
because they indicate general environmental degradation—with
implications for the health of other animals, humans included—and
because amphibian species, like vanishing rain-forest plants,
are a potential source of new drugs. "Many frogs produce
chemicals [and poisons through their skin] which could have
huge applications in healthcare and medical treatment,"
he said.
Specimens of the newly discovered species were first collected
in 1993 when Rohan Pethiyagoda, founder of Sri Lanka's Wildlife
Heritage Trust based in Columbo, arranged to survey animal
biodiversity in the nation's surviving rain-forest patches.
The island has lost 95 percent of the rain forests it once
had, with remaining patches covering around 750 square kilometers
(290 square miles)—less than 2 percent of the island.
Many of the forests were cleared during the British colonial
period, when the island was known as Ceylon, to make way for
rubber, coffee, and tea plantations.
Remarkable Discovery
Pethiyagoda and his team collected over 1,000 frog specimens
at 300 sites during the course of their extensive survey.
When they attempted to identify the species they had collected
they ran into considerable difficulty matching the animals
to Sri Lanka's known frogs, said Schneider. International
experts later confirmed that the researchers had turned up
many previously undescribed species, said Schneider.
Subsequent work comparing the relationships among the species
with the use of physical appearance, ecological similarity,
frog vocalizations, and genetics helped confirm the novel
nature of the animals. Pethiyagoda, and his team also compared
the animals to Sri Lankan frog specimens in museums worldwide,
to ensure none of the species had been previously described.
Pethiyagoda, Schneider and their colleagues detail the discovery
in the October 11 issue of the journal Science.
The fragmented nature of Sri lanka's rain forests, which
are separated by grassland in some places, may have contributed
to the large number of species, said Wilkinson. As direct-developing
frogs are effectively stranded in habitats which have high
humidity, the animals may have been divided into distinct
breeding groups that over time diverged into separate species.
This remarkable discovery could mean that there are other
vertebrate species waiting to be found across the tropics,
said Schneider. "No other tropical rain-forest region,
apart from Australia, is likely to have been as thoroughly
surveyed as the Sri Lankan rain forests," he said. "Therefore
we expect that there is substantial unknown diversity in tropical
regions worldwide."
Copyright
National Geographic
Reprinted from http://news.nationalgeographic.com/news/2002/10/1010_021010_srilankafrogs.html
