Endangered reptile species and populations
Without the vociferous public support many other animals enjoy, reptiles may have a tough time weathering the growing threat of extinctions caused by the march of human development.
A brown spider vanishes from its leafy perch, displaced by a flashing white blur - the long, sticky tongue of a chameleon. A foot and a half away, the hunter snaps his mouth shut, then crunches down on his prey several times before swallowing. Splotched with bursts of lime green, kelly green, and white, the chameleon, locked to its leafy perch by clasping fused toes, is a perfectly adapted predator in the forests of Madagascar. But many Malagasies are not aware of the important role chameleons play in their forest habitat. In fact, island taboos erroneously label them as poisonous creatures, and often they are considered harbingers of bad luck. Still others see them merely as a color-changing novelty and revenue source - much in demand by the largely unregulated international pet trade.
More than half of the world's 100-plus chameleon species live only on the island of Madagascar, and most of them in its forests. But the island is also home to a burgeoning, resource-hungry human population of 12 million, which grows by 3 percent every year. Already, more than 80 percent of Madagascar's native forest has been cleared, felled by chainsaws and axes. And as habitat disappears in this crowded country, which is roughly the size of France, chameleons disappear along with it.
The plight of Madagascar's chameleons is only a microcosm of the pressures facing a vast number of reptiles today. Increased human activities have pushed many of these ancient creatures to the verge of extinction. Worldwide, at least 21 reptile species have completely vanished within the last 400 years - and these are likely only the tip of the iceberg. The 1996 World Conservation Union's (IUCN) Red List of Threatened Animals reports that 20 percent of reptiles for which there "is adequate information to assign a conservation status" are threatened with extinction: 3 percent of these are "critically endangered;" 5 percent "endangered;" and 12 percent "vulnerable."
Many reptiles share the plight of the chameleon, in that they engender intense fear or fascination in people - whether through physical encounters or through the archetypal role they play in the legends and lore of human cultures. Some cultures regard reptiles as powerful religious symbols. The cobra plays a prominent role in Hindu religion, representing Shiva, the god of fertility and death; the plumed serpent Quetzalcoatl was the chief object of worship in Aztec culture, representing fertility, death, and resurrection; the turtle generously agrees to support the earth on its shell in Mohawk and other Native American creation myths; and Australian Aborigines associate a giant rainbow serpent with the creation of life. But perhaps the most telling portrayal of reptiles - reflecting a widely prevalent attitude toward reptiles today - is the serpent described in the Book of Genesis that deceived Adam and Eve, and prompted their fall from innocence. This stigma of reptilian evil has retained a strong grip on the popular imagination, as reflected, for example, in the recent Hollywood film Anaconda, a horror-filled tale of a 12-meter-long, human-eating snake. But today, reptiles have much more to fear from humans than humans do from them.
Reptiles tend to keep low profiles - crouching under rocks, crawling through undergrowth, hiding under water, or perching in trees - and often, especially in the case of research and conservation priorities, out of sight has been out of mind. Unlike birds or frogs, reptiles do not burst into song, and they do not capture the attention of as many biologists as charismatic large mammals do. Consequently, the distribution, ecology, and basic biology of most species remain poorly studied. In fact, the scientists who compiled the Red List were only able to fully assess three of the six reptile orders: the crocodilians, the testudines (turtles, tortoises, and terrapins), and the lizard-like tuataras, each of which ranked high in the number of threatened species - 43 percent, 38 percent, and 50 percent, respectively. But the two largest orders - those of snakes and lizards - were not fully analyzed, nor was the order of legless amphisbaenians. Given these research gaps, and the high number of threatened species in the three fully assessed orders, the Red List's authors surmise that "the overall estimate of 20 percent of reptiles species as threatened is probably low for the entire class."
Although relatively little research has been done to reveal the magnitude of their ecological contributions, reptiles are an indispensable part of many ecosystems - helping to assure the health and stability of their habitats. From clothespin-sized anolis lizards hunting on the walls of Caribbean hotels to eight-meter-long pythons living in the jungles of Southeast Asia, reptiles act as critical links in ecological food chains. We are just beginning to appreciate their roles in regulating pest and insect populations, providing habitat for other species, and maintaining the stability of ecosystems as key predators. For example, in North America, owls, foxes, and rat snakes all prey on white-footed mice, but only the rat snake can crawl into a small burrow to catch a mouse and its young. The rat snake, which is common throughout much of the mouse's range, plays a major role in controlling populations of these abundant rodents.
"Reptiles exert significant control pressure on several other animal groups that pose problems for people, notably rodents and insects," says IUCN crocodile specialist Perran Ross. In overgrown areas, in forests, deserts, and even inside homes in the subtropics and tropics, small lizards such as geckos catch innumerable insects and other invertebrates, helping to curtail disease-spreading insect populations. In South America, the alligator-like black caiman has traditionally curbed populations of rodents called capybaras. But plummeting caiman populations have allowed the capybaras to flourish, which in some areas has caused significant damage to croplands. In India, cobras and rat snakes are integral to suppressing pest populations - but the eradication of snakes in some Indian agricultural areas has caused populations of crop-damaging rodents such as rice rats and lesser mole rats to skyrocket. Without the invaluable ecological service of the snakes, notes acclaimed naturalist Guy Mountfort, "India might be unable to feed itself." South America's caimans and Asia's gharials, both crocodilians, have been credited with helping keep fish diversity in balance by feeding on predatory fishes that would otherwise overwhelm other, often more commercially valued, species. In addition, caiman excrement likely recycles nutrients in water, turning otherwise food-poor stretches of Amazonian backwaters into important nurseries for fish fry.
Some of the largest species of reptiles, such as Komodo dragons, boa constrictors, and Nile crocodiles, are top predators - able to drag down and kill wild pigs, deer, and giraffes, respectively. Large tortoises and iguanas inhabiting islands, such as Ecuador's Galapagos Islands, fill niches as top grazers, cropping fragile vegetation but not causing devastation like the goats and cattle that have been introduced into much of their habitat. These iguanas and tortoises are important plant dispersors, facilitating the germination of seeds that pass through the animals' digestive systems.
The American alligator is a prime example of what scientists call a keystone species - one on which other species depend for survival. In Florida's Everglades, these leathery skinned reptiles dig pools for themselves in the dry season and dredge up materials for their mound nests in wet spring months. The "alligator holes" resulting from these excavations become oases where aquatic invertebrates, fish, amphibians, other reptiles, water birds, and mammals such as raccoons ride out the bone-dry months until the rains return, allowing them to disperse again. In addition, alligators' repeated travels over muddy Everglades marshes may also affect drainage patterns by creating shallow streams. The tops of their raised mound nests provide unusually high surfaces that remain dry enough in wet months to support myrtle and other small trees that could not survive in the surrounding low marshes.
The long burrows of the gopher tortoise of the southeastern United States similarly provide homes and shelter for varied animals, including gopher frogs, rodents, and North America's largest serpent, the harmless indigo snake.
While it is not clear exactly how many reptile species are in imminent danger, there is no question about the cause of their decline: as the human population continues to surge, the forests, plains, wetlands, and deserts inhabited by reptiles arc increasingly besieged - chopped down, paved over, built upon, filled in, or plowed under. Following at the heels of human development are the attendant domestic animals - plant-munching goats, sheep, and cows, as well as voracious predators, such as cats, mongooses, and dogs. In addition, many reptiles are threatened by increasing pollution of rivers and waterways, roads bisecting habitats, and a booming exotic animal trade.
From wetlands to deserts, the habitat of reptiles is being steadily taken away, and unlike flying birds or swift-running mammals, most reptiles cannot quickly escape and seek greener pastures when their habitats are destroyed. They simply disappear, destroyed with their homes. The bog turtle of eastern North America has all but vanished from most of its range due in good part to drainage of its wetland habitats, including swamps and wet meadows. One of Great Britain's only two lizards - the sand lizard - is endangered due to development and disturbance of its dune and heathland habitats. Meanwhile, in South Africa, the geometric tortoise has lost all but 10 percent of its arid lowland habitat on the Cape Peninsula. The situation is compounded in tropical rainforests, which contain by far the greatest diversity of reptiles but have received only limited study by scientists doing reptile surveys.
In these forests hundreds of species are threatened. The concentration of diversity, and the subsequent potential for loss is astounding - nearly 75 different snake species have been found in one patch of Peruvian rainforest about the size of a typical city, according to snake specialist Harry W. Greene in his book, Snakes: The Evolution of Mystery in Nature.
Pollution is also taking a toll on reptiles, undermining both the health of the animals and the stability of their ecosystems. For example, a chemical spill into Florida's Lake
Apopka in 1980, combined with the constant infusion of agricultural chemicals from nearby farms, has severely disrupted reproduction in local alligator populations. The spill released dicofol, a pesticide known to be contaminated with DDE, a DDT byproduct. Ongoing studies of the lake's alligators and turtles have found that alligator eggs hatch at less than half the normal rate, and many of those that do manage to break out of their eggs suffer from abnormal sexual development (see "Synthetic Chemicals on the Loose," March/April 1997). Related studies are underway to examine the lake's largemouth bass and water birds, some of which have laid eggs with abnormally thin shells.
A rapidly growing strain on reptiles, especially on rare and endangered species, is the hunting and commercial collecting of skins and animal parts for a poorly regulated international animal trade. The worldwide market for illegally traded plants and animals last year reached an estimated $10 to $20 billion, with reptiles making up a considerable part of that. Evidence of unsustainable exploitation of reptiles is abundant - the wildlife trade watchdog organization TRAFFIC USA reports that around 125,000 rattlesnakes are caught and killed annually in the United States for their meat, skins, gall bladders (to be used in traditional Asian medicines), or to be sold as souvenirs. This unregulated industry centers on "rattlesnake rodeos" held in a number of states, where thousands of snakes are captured and kept in inhumane conditions until they are traded and killed. Supporters claim that these events purge areas of the potentially deadly rattlers. But scientists worry about the possibility of an ecological backlash in the areas where these snakes play an important role in regulating natural conditions, including curbing rodent populations. (Only about six deaths occur each year in the United States due to venomous snake bites.)
With human population and appropriation of resources rising rapidly, many reptiles now face serious threats from multiple sources. Sea turtles - highly vulnerable due to their slow growth patterns - are tangled and drowned by the thousands each year in fishing nets. In just one survey, 5,282 dead olive Ridley sea turtles washed up on the beaches of India's Orissa state between December 1993 and May 1994, virtually all killed by fishing nets located off the shores of their nesting beaches. And on beaches in most parts of their ranges, sea turtle nests are often raided for their eggs and adults dragged off to market and butchered. Meanwhile, in beach resort areas, the nestlings that do hatch and emerge from the sand instinctively clamber toward the first light they see - in many cases the electric lights of the resorts rather than the moonlit sea, a wrong turn that usually kills them.
The Madagascar radiated tortoise, a species that is found only on the island of Madagascar and can live for nearly a century, is now listed by the IUCN as vulnerable-threatened with extinction in the not-too-distant future. Not only are goat herding, road building, and deforestation accelerating the tortoise's loss of habitat, but the spectacular star patterns that adorn its shell are making it a prize for reptile collectors, who will pay up to $10,000 for a single contraband radiated tortoise.
A study of South America's caimans, published in the conservation journal Oryx, illustrates how once-plentiful species have buckled under growing multifaceted pressures. The 1996 survey found that black and common caimans in Brazil have rapidly disappeared from many areas due to the dumping of industrial wastes, including mercury and lead released from gold mining operations, especially in heavily settled states like Rondonia. More than half the animals sampled in the caiman survey had startlingly high levels of lead in their tissues. In addition, the conversion of riverine forest to agricultural and range land has caused increased soil erosion and siltation, which in turn has sullied the wetland habitats that support the caimans. Many hunters also kill the animals for food and for their skins, which are illegally exported for the leather trade. All of these factors have taken a devastating toll: over the course of the survey, which was conducted between 1985 and early 1992, black caimans completely disappeared from 41 of the 47 areas studied, while common caimans vanished from 4 of 39 sites, and declined in many more.
In some cases, human-caused threats to reptiles may be quietly altering their evolution. Researchers from the University of New Mexico found that lava lizards, endemic to the Galapagos Islands, were generally smaller, more difficult to find, and much more skittish on those islands inhabited by introduced cats. These characteristics likely surfaced over the 200 years these exotic feline predators had been present, driving lizards to reproduce at a younger age and at a smaller size, and selecting against lizards with elaborate displays or ornamentation. The researchers concluded that "exotic predators and native prey can coexist. However, the relationship can still result in reduced biological diversity and altered evolutionary trajectories."
The myriad pressures facing reptiles are compounded on islands, where reduced area magnifies the effects of habitat destruction and exploitation. In addition, exotic species introduced to an island often compete with, and prey upon, island endemics, many of which have not evolved to cope with predators. The intensified microcosm of environmental pitfalls on islands offers scientists early warning about the pressures facing reptiles worldwide.
For example, all nine endemic West Indian iguana species - large reptiles that were among the first colonizers on these islands - are threatened with extinction due to predation by introduced mongooses and dogs, along with habitat destruction. And on the Galapagos Islands, scientists have noted a striking absence of young marine iguanas on five islands that are inhabited by feral cats. Left unchecked, these cats may cause the extinction of these populations once the remaining adults die out.
The situation is just as serious for tuatara, which resemble lizards but represent the sole two remaining species of an order that flourished before the heyday of the dinosaurs. Today, tuatara live only on islets off the coast of New Zealand, having been driven out of much of their historical range by introduced rats and habitat destruction wrought by Maori and European settlers. Scientists studying tuatara populations living on small, rocky islands, which are also inhabited by introduced Polynesian rats, believe that the rats compete with the earth-toned, spike-headed tuataras for food, and prey on their young. Costly reintroduction and rat eradication programs are underway to save the last of these primitive reptiles - efforts that also benefit the island's nesting seabirds and other native fauna.
Reversing the decline of reptile populations and restoring them to healthy levels will require developing solutions as diverse as the problems reptiles face and the habitats they need to survive. Most reptiles live in tropical countries that face serious economic and social problems. Wildlife conservation programs are often too costly, or too poorly managed, to be widely effective in many of these countries. Meanwhile, in other countries, booming economic growth has spurred widespread development that is quickly swallowing up valuable habitats outside of designated parks and wildlife refuges.
As healthy reptile habitat continues to dwindle, a small but energetic cadre of scientists is scrambling to preserve priority "hotspots" - areas which contain an unusually concentrated number of species - so as to make efforts to conserve reptiles and other fauna more effective. A report published in 1997 by researchers at the U.S.-based Environmental Defense Fund (EDF) and Princeton University, plotted areas of the United States, county by county, with the highest occurrence of endangered species. The data revealed that analysis of reptiles', amphibians', and birds' ranges can be an especially good way of predicting where other imperiled species might occur. The greatest diversity of endangered reptiles in North America were found to be located in several coastal areas around the Southeast, along the east Texas coast, and in Southern California. By selecting carefully, writes researcher David Wilcove, "we can protect a great many endangered species on a relatively small amount of land."
By mapping hotspots, conservationists have found some significant overlap between classes of animals that offer synergistic preservation opportunities. For example, a 1992 study by BirdLife International reported significant habitat similarities between birds, reptiles, and amphibians in Central America and the Caribbean - especially for endemic species. The rare West Indian snake Chironius vincenti, found only on the island of St. Vincent, has habitat needs that closely match those of the endangered St. Vincent parrot, the national bird of St. Vincent and the Grenadines. Both species are threatened by deforestation, but efforts to protect the parrot by setting aside rainforest habitat, and to educate islanders about the parrot's plight, will also inadvertently benefit the snake.
As on St. Vincent, reptiles in other parts of the world ride on the coattails of high-profile species that require larger expanses of habitat. Some examples include the reptiles protected in sanctuaries for tigers in India and big mammals like elephants in Africa. But incidental protection of reptiles and the preservation of biological hotspots cannot be counted on to work across the board. Localized species, which face the most imminent threat of extinction, are largely found outside existing park or reserve boundaries.
Creating wildlife refuges and setting aside parklands are important links in the diverse strategy that is needed to stabilize reptile populations. But protecting key tracts of land for conservation can often be politically impossible, and purchasing land as well as properly training wardens may prove either prohibitively expensive or difficult if there is not support from local communities. S. K. Eltringham, a British zoologist who has written extensively on wildlife conservation issues, notes: "The problem with wildlife is that the people who wish to preserve it are rarely those who have to pay the cost." In response to these and other concerns, a number of conservationists in recent years have turned away from strict, "protectall" conservation strategies, and many - including those at the IUCN - advocate the sustainable commercial use of wildlife where possible, including the commercial use of some reptiles.
Increasingly, commercially valuable reptiles are being used in ranching operations that legally utilize wild populations. The theory is that by making reptiles a commodity, local communities will view them as a financial asset to be protected and fostered (see "The Price of Habitat," May/June 1997). Together with conservation efforts aimed at protecting less-commercially valuable species, such operations can be part of integrated harvesting programs that combine sustainable use of other products, such as nuts, timber, fruit, and medicinal plants, from the reptiles' habitats.
The dusty scrub jungles and farms of the Chinglepet District, near Chennai (formerly Madras), India, have been the proving ground for a remarkably successful program that integrates the needs of a snake-catching community, its reptile resources, and sustainable commerce. The Irula tribe, now numbering more than 20,000, has subsisted for years on the capture of poisonous snakes and other animals. Traditionally the Irula, who worship the cobra as an incarnation of a deity and believe snakes bring them good fortune, sold the skins of the snakes they captured.
In 1978, the Indian government banned the export of snake skins, which threatened to undermine the tribe's way of life. But herpetologist Romulus Whitaker helped the tribe establish the Irula Cooperative Venom Center as a way of preserving their traditional way of life and well-being. The Tamil Nadu state forest department agreed to allow Irulas to capture such poisonous snakes as cobras and kraits, milk them for their venom, and release them in forest reserves. Today, income generated by the sale of venom, used to produce snake-bite antidote, and admission of tourists to view the venom-milking activities enables the cooperative to cover basic costs and make a profit. It is now the largest venom producer in the country.
Zimbabwe is home to another example of a felicitous marriage between conservation and commerce - a highly successful Nile crocodile ranching program. In the wild, most crocodile eggs succumb to the vagaries of weather or are devoured by monitor lizards, large birds, or other predators. In recognition of this fact, Zimbabwe's national parks department authorized crocodile farmers to collect wild eggs and raise them for profit - with the caveat that they release two percent of their harvest into the wild; the rest are slaughtered for their skins. The country's 50,000-strong wild crocodiles are now thriving, and the captive crocodile population is now about three times the size of the wild population. The program has been a definite success, generating $2.8 million in 1994 alone. The Zimbabwe population of Nile crocodile remains on Appendix II of CITES, the United Nations Environment Program's Convention on International Trade in Endangered Species - its trade carefully monitored, but not banned.
Since 1971, the Nile crocodile and six other crocodilians, including the American alligator and Australia's saltwater crocodile, have been downlisted from endangered status thanks in good part to protective measures and, to a lesser degree, carefully monitored ranching operations. Similar commercial projects have been proposed, or have begun, for fast-breeding, high-demand reptiles such as green iguanas (relished for food and the pet trade), South American tegu lizards (valued for their skin), and Asian geckos (prized in traditional Asian medicine). Such projects, if carefully and responsibly run, could lower demand for wild-caught animals, allowing populations to stabilize. Despite some successes, most of these reptiles arc still heavily harvested in the wild, and some critics accuse ranching proponents of trying to commercially justify trade in declining species.
Other sustainable activities can include, where infrastructure and tourist appeal allow, ecotourism operations. Some of the more popular ecotourism destinations include the Galapagos Islands, where reptiles feature prominently among the photogenic fauna, and the Indonesian islands inhabited by the endangered Komodo dragon. These hotspots bring in many tourist dollars, but fight restrictions on the number of visitors, their access to fragile habitat, and their behavior must be in place for ecotourism to be a benefit rather than a detriment.
Under the mounting pressures of human-driven habitat destruction and destabilization, it is increasingly clear that the future of reptiles and the ecosystems that support them will depend on our ability to make effective conservation and development decisions today. There is a great need to conduct comprehensive surveys of areas - especially in the tropics - to fully assess the current diversity and status of reptiles. The few exhaustive surveys that have been conducted have reaped great rewards. Ongoing work by scientists scouring remaining habitats in Madagascar and Cuba since the mid-1980s has not only revealed much about largely unstudied reptiles, but has also uncovered dozens of previously undiscovered species. These censuses could not have come at a more critical time: both of these island nations have already lost at least 80 percent of their forests, as well as a majority of their wetlands. Further studies can promote conservation of the remaining biodiversity in these and other species-rich countries in the future.
While careful studies and conservation strategies are needed, long-term protection of reptiles can only be assured through successful partnerships between local people, community organizations, and governments. Sound laws and enforcement, coupled with education and, where possible, economic incentives for conservation, may be the best hope for balancing human resource demands with the basic habitat needs of reptiles.
Like a handful of threads in a tattered and fraying tapestry, the decline of reptiles is part of a much larger unraveling - a loss of biodiversity that is placing increasing stress on the earth's ecosystems. As the planet's human population continues to surge, it may be increasingly difficult for many people to appreciate the plodding ways of reptiles - and the parts played by other creatures that connect us to and sustain our ecosystems. In today's fast-paced world, where a computer transmission can seal the fate of a thousand-hectare forest ecosystem in less than a second, it seems we could certainly learn a thing or two from tortoises and their relatives; after all, they have 200 million years of experience on us.
I can do one of three things with these [endangered] boas. I can leave them alone, and not have enough to eat. I can eat them. Or I can sell them to people. I make enough from selling one snake to eat for a month - or more. What would you choose? - A farmer in Madagascar, quoted by Donoran Webster in The New York Times Magazine
The worst thing that can happen - will happen - is not energy depletion, economic collapse, limited nuclear war, or conquest by a totalitarian government. As terrible as these catastrophes would be for us, they can be repaired within a few generations. The one process ... that will take millions of years to correct is the loss of genetic and species diversity by the destruction of natural habitats. This is the folly our descendants are least likely to forgive us. - Edward O. Wilson, Harvard Magazine
Howard Youth, former associate editor of WORLD WATCH, writes frequently on wildlife issues. His work has appeared in WORLD WATCH, the Vital Signs series, Wildlife Conservation, EDF Letter, and other publications. He currently works at Friends of the National Zoo as associate editor of ZooGoer magazine.
©1997 Worldwatch Institute
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