London - Scientists have identified more than 100 new species of frogs inhabiting a small and threatened patch of tropical rainforest in a discovery that underscores our ignorance of the natural world's immense diversity.
The new species are all tree frogs living in the rainforests of Sri Lanka and are the latest additions to the estimated 1,7 million species of animals and plants known to science. However, increasingly scientists believe that the actual number of species on Earth is many times this number - possibly 10 million or more.
An international team of biologists led by Christopher Schneider of Boston University describes up to 140 new frog species they found in a survey of Sri Lankan rainforests published this week in the journal Science. The researchers say that the island is an "amphibian hotspot of global importance" in terms of biodiversity.
"We have only just begun the process of describing them and giving them names. They range in size from about an inch to four inches and come in all colours," Dr Schneider said.
Over recent years, herpetologists have monitored a dramatic global decline in amphibians - frogs, toads, newts and salamanders - so it has come as a surprise to many of them to discover a place where so many tree frogs have survived unnoticed.
"Sri Lanka is well explored and has has been studied by many British naturalists so it has come as a surprise to find so many frogs," Dr Schneider said.
Some of the newly-found frogs lay their eggs in foam nests in trees and bushes overhanging streams. When the tadpoles reach a certain size they drop into the water where they continue their metamorphosis into frogs.
Other species, however, belong to the rhacophorine group of frogs which lay eggs in the forest leaf litter that develop directly into tiny froglets, bypassing the typical aquatic phase of the amphibian lifecycle.
Dr Schneider said this adaptation may explain why these species have managed to survive in a rainforest that in recent decades had dwindled dramatically to just five percent of its original size. "By skipping the aquatic [stage], they may bypass a life stage when they are more vulnerable," he said.
The discovery of so many new species on Sri Lanka increases the number of frogs there by fivefold. The concentration of amphibian diversity on the relatively small island puts the country on a par with much bigger islands, such as Madagascar and Borneo, in terms of biodiversity, the scientists say.
Rohan Pethiyagoda, a researcher at the Wildlife Heritage Trust in the capital Colombo, began a census of Sri Lanka's disappearing species in 1993. To his surprise he kept finding frogs he could not identify during this treks through the 750 square kilometres of Sri Lankan forest - which once covered 15 000 square kilometres.
From studies of about 1 000 specimens the researchers narrowed down the number of possible species to about 200. Subsequent genetic studies and other forms of analysis confirmed that between 120 and 140 were new to science.
The scientists also compared their frogs with other specimens kept in museums and collected more than 100 years ago. They found that upto 100 species that had been collected in Sri Lanka more than 100 years ago were not among the current finds, suggesting they have since gone extinct.
Such research exemplifies the problems facing scientists trying to study and preserve global biodiversity. Animals and plants may be going extinct at a faster rate than they are being documented and classified.
Stephen Blackmore, the Regius Keeper of the Royal Botanic Garden in Edinburgh, says in a separate article in Science that documenting the world's animals and plants represents one of the most important goals following the World Conference on Sustainable Development in Johannesburg this summer.
"The documentation of life on Earth, on which our own well-being ultimately depends, surely deserves to be amongst our most urgent priorities for investment," Dr Blackmore says.
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