Given the pace of new species discoveries from recent karst surveys, "it is likely that several species on unexplored karsts undergoing quarrying are disappearing right under our noses," Clements added.
The world's smallest mammal, the bumblebee bat, is found exclusively in a small number of karst caves in Thailand.
Other rare mammals associated with the limestone outcrops include Francois's leaf monkey, the serow (a type of goat antelope), and a newly found rodent from Laos that represents the first new mammal family to be discovered in 30 years (see rock rat photo).
The researchers say that 31 karst-living species in Southeast Asia are currently recognized as globally threatened by the World Conservation Union (IUCN). But the true figure is likely to be far higher.
Animals and plants found on karsts are seriously underrepresented in lists of endangered species, "in part as a result of undersampling and data deficiency," the team writes.
As a result, IUCN figures are geographically skewed, Clements says.
"For example, 18 of the 20 threatened karst-associated land snails occur from just one country, Malaysia," he said.
"Given that other scientists have recorded high levels of land snail endemism from other countries such as Thailand and Vietnam, I expect the current figures to be severely underestimated."
Lack of Knowledge
Most cave-dwelling karst species, which include bizarre forms of blind fish, crabs, and crayfish, have not even been subjected to any sort of threat analysis, the study says.
"Cave-dwelling organisms are generally overlooked because they are uncharismatic and difficult to study," Clements said.
"Such organisms are therefore considered as 'data deficient' by the IUCN because very little is known about their basic biology, and it will be hard to make a case for their conservation."
Researchers from Brigham Young University in Provo, Utah, last year reported that just three hours of sampling in a well-known karst cave in Malaysia turned up at least three invertebrate species that are likely new to science.
Since 1988, 13 new fish species have been discovered in karst caves in Southeast Asia, including a blind loach that climbs onto rocks using its fins.
Despite their wealth of unusual fauna, karsts remain poorly studied generally, Clements says.
"You will be hard-pressed to find information on karst ecosystems in ecology textbooks," he said. "Such general apathy, coupled with the difficulty of performing biodiversity studies on the rugged karst terrain, make them unpopular study systems in the scientific community."
Pressure to mine karsts for limestonewhich is used to manufacture commercially valuable products such as cement and marbleis likely to increase, the study warns.
Using mineral statistics spanning 1999 to 2003, the research team estimated levels of limestone quarrying in tropical regionsincluding Africa, South America, and Central America.
Southeast Asia showed the greatest annual average increases in limestone quarrying5.7 percent a year.
Such quarrying rates, the team says, "suggest a bleak outlook for the future of regional karst biodiversity."
"Isolated karsts around densely populated areas with emerging construction industries and reasonable infrastructure are most susceptible," Clements added.
Quarrying should be confined to larger and more extensive karst areas, the researchers say. Small and isolated karsts should not be mined, as they are more likely to harbor unique plants and animals.
While about 13 percent of Southeast Asia's karst area has some level of protected status, protection is still absent or minimal in countries such as Cambodia and Myanmar, the researchers add.
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