Their heads and bare faces fringed by Bozo the Clown hair, high-flying gibbons are often called the greatest acrobats of the animal kingdom. Using their hands like hooks, these small apes swing through the canopies of Southeast Asian rain forests at breakneck speed, often leaping 30 feet between tree limbs.
Among the few monogamous primates, gibbons are also great vocalizers: their songs and cries carry more than a mile. Yet nearly all nine species of gibbon are imperiled through much of their range -- none more than the silvery gibbon, named for its distinctive color and found only on the Indonesian island of Java.
Experts estimate that in the last 25 years, the number of silvery gibbons has plummeted to fewer than 2,000 and perhaps fewer than 400 from 20,000. The pressure on the surviving animals is enormous, with many barely hanging on in shrinking fragments of forest, said Dr. Don J. Melnick, executive director of the Center for Environmental Research and Conservation and a professor of biology at Columbia University.
Dr. Melnick and a team of researchers from the United States and Indonesia recently completed a genetic study of silvery gibbons and found that the species split around 100,000 years ago into two groups or lineages. The researchers have proposed that wildlife officials manage those two lineages separately to let them follow what appears to be a natural evolution that could ultimately lead to a new subspecies or even a new species, though no one can predict how long that may take.
That approach will also prevent the loss, through interbreeding, of groups of genes that have evolved and now work together to provide each lineage with unique characteristics, like immunity to certain diseases, Dr. Melnick said. (The Indonesian government, preoccupied with political and economic turmoil, has not acted on the researchers' proposal.)Continue reading the main story
While potentially significant for the long-term survival of silvery gibbons, the research also shows the way genetic, demographic, behavioral and ecological studies are increasingly being used to understand the relationships among groups of animals that have become fragmented and genetically isolated through habitat loss and other human activities. Researchers can then plan ways to overcome those problems in the wild, avoiding costly and largely ineffective captive breeding programs.
''A hidden time bomb in today's world is the loss of genetic diversity within species,'' Dr. Melnick said. His conservation genetics laboratory at the research center -- a joint venture of Columbia, the Wildlife Conservation Society, the American Museum of Natural History, the New York Botanical Garden and the Wildlife Trust -- is working to try to keep that bomb from exploding for more than 100 endangered species, from salamanders and toads to Asian elephants and Java rhinos.
Where groups are isolated in dangerously low numbers from other members of their species, the loss of genetic variability through inbreeding becomes a major threat to survival, says Dr. Alan R. Templeton, a professor of biology and genetics at Washington University in St. Louis. Inbred groups can develop dangerous mutations, lose their resistance to infection and disease and easily fall prey to environmental upheaval. Potentially beneficial genetic and behavioral adaptations that appear in the isolated group cannot spread through the species.
When isolated groups cannot be linked through protected wildlife corridors, humans must move animals around to try to restore historic gene flows, said Dr. Keith A. Crandall, an assistant professor of zoology at Brigham Young University. Java and other islands of Indonesia present particular problems for such intervention with a number of species. One of the most densely populated islands in the world, with 115 million people, Java has lost 91 percent of its forests, and the expanding population demands ever more land. Protection of forests and animals is poor, conservationists say.
''Keeping land in Java free from development is very difficult,'' Dr. Noviar Andayani, secretary of the Center for Biodiversity and Conservation Science at the University of Indonesia, said in a telephone interview from Jakarta. ''With the current economic crisis, there are even more problems.''
Dr. Andayani, Dr. Melnick and three collaborators published their analysis of the silvery gibbons' mitochondrial DNA -- that is, DNA inherited through the mother -- and recommendations for saving the endangered apes in the June 2001 Journal of Conservation Biology.
Java's last silvery gibbons are confined to 23 isolated parks and unprotected patches of lowland evergreen rain forests, Dr. Andayani said. Some of those forest fragments hold no more than 10 gibbons, a number that cannot sustain itself. Gibbons are easy prey for people and dogs when they try to cross farms, she added, and an illegal pet trade further depletes their numbers.
The more stable of the two silvery gibbon groups, called the western lineage, numbers in the hundreds and lives in and near Gunung Halimun National Park. The central lineage, also in the hundreds, occupies scattered pockets of forests and parks on the east side of the peaks around Gunung Salak, which can rise above 6,000 feet. (Gunung means mountain.)
Although the reasons for the initial split between the two lineages are still unknown, the researchers suggest that silvery gibbons find the high montane forests around Gunung Salak inhospitable and refuse to enter them. Dr. Andayani plans more detailed studies of the region to make sure no silvery gibbons live there and to try to determine when and why the area became a barrier.
The genetic split in silvery gibbons is ancient enough, at 100,000 years, that the scientists have recommended against a plan to mix the western and central populations unless there is no other way to preserve the species. The researchers propose instead to move animals between forest fragments to increase genetic diversity within the central groups. The plan is to capture young gibbons preparing to leave their families and take them to other carefully selected areas.
The decision to link isolated groups of animals requires a complex analysis of how and why their genetic differences arose. Wildlife biologists must determine whether the differences result from natural processes, like shifts in geology or climate, or from human activities, said Dr. Rodney L. Honeycutt, a professor of genetics at Texas A & M. Researchers should also examine whether the isolated group fills a different ecological niche or exhibits unique behavior, Dr. Honeycutt added.
If the genetic differences result from human activities or are not very pronounced, a number of experts say, the isolated group should be brought back into the greater species gene pool. But if the genetic split appears to be the result of natural processes or the group shows signs of unique behavioral and ecological adaptations, scientists should avoid interbreeding. And the final decision should emphasize preserving as many animals and as much variability as possible, even if that means losing some unique characteristics.
''Philosophically, what we are trying to do is preserve adaptive diversity,'' said Dr. Robert Wayne, an evolutionary biologist at the University of California at Los Angeles, ''and we have to develop a framework for doing that.''
Many experts agree that the most successful genetic recovery program to date involved the introduction of eight Texas cougars to South Florida in 1995 to alleviate intensive inbreeding that was driving the elusive Florida panther to extinction. Wildlife biologists acknowledge that the panthers remain geographically isolated and will probably require infusions of new genes about every 20 years. But for now they have been revitalized.
In recent years the tools for genetic analysis have grown stronger and more complex. Examining DNA, biologists can identify individual animals and their lineage, measure their age and determine whether they are breeding.
In 1995, Dr. Templeton, of Washington University, created a computer program to determine genetic relationships among and within species based on an examination of specific haplotypes, clusters of genes that are inherited as a unit. The program helps researchers determine whether groups of animals have become fragmented because of natural forces or human actions, he wrote in the March 2001 issue of the journal Molecular Ecology.
It is available to other researchers through Dr. Crandall's Web site at Brigham Young. The program also indicates whether a given group of animals represents hybrids between two distinct species or subspecies and, tracking the spread of specific mutations, reveals the historical movement of animals into new territory, Dr. Templeton said. It also points to ''natural and historical forces that contribute to speciation.''
But if sophisticated genetic studies are to become more than academic records of the path to extinction, scientists say, then officials and people concerned about conservation must commit themselves to preserving land and animals, and scientists and conservationists must find ways to increase legal protection and public support for imperiled animals like the acrobatic silvery gibbon.
Providing those ''adorable creatures'' a future in their native habitat, said Dr. Andayani of the University of Indonesia, will also benefit a host of other animals struggling to survive in the vanishing Javan rain forest.Continue reading the main story