Reptiles are frequently secretive, and knowledge of their biological status often is based on anecdotal information rather than on precise scientific data. Nonetheless, scientists have identified certain characteristics, which make some reptiles particularly vulnerable to changes in their environment. Species that are large; island dwelling; restricted in distribution, habitat, or ecological specialists; require large home ranges; are migratory; or are valued as food or medicine or for their skin are most likely to show population declines when stressed by human activity. In combination, as when a large species used for food lives on an island, these characteristics have made some reptiles extremely susceptible to human influences. In addition to the spatial, size, and behavioral characteristics that make reptiles vulnerable to extinction, certain life history traits, such as delayed maturity, slow growth, a low reproductive output, and high juvenile mortality rate, combine to make recovery difficult for many species. The difficulty arises because these biological traits are the product of a long-term evolutionary history and are slow to respond to rapidly changing conditions brought about by human activity. Because some species have long generation times, they cannot adapt to rapid environmental change or even to well-intentioned conservation management.

It is difficult to determine how many reptiles are endangered worldwide or even to guess at what percentage is threatened. Some groups, such as turtles and tuataras, are declining because they are affected adversely by humans and because they possess the aforementioned life history characteristics that make them exceedingly vulnerable to environmental change. Examples of reptiles in need of the highest-priority conservation efforts include the giant tortoises of the Galápagos and Seychelles, seaturtles, the giant land iguanas of the Caribbean, the Canary Islands giant lizard, several crocodilians (e.g., the Chinese alligator, the Siamese and Philippine crocodiles, the tomistoma, and the gharial), and the two species of tuataras in New Zealand. The following sections provide a broad overview of reptile conservation, the factors that affect reptiles, and the tools available to biologists to reverse declines and to enhance prospects for long-term survival.

Scope of the problem

Of the four reptile lineages, turtles (Chelonia) are the most threatened of the major groups. More than half of the 264 or so recognized species face serious population declines or even extinction. Nearly all tortoises require concerted conservation management, as do the seven species of seaturtles. The regional turtle fauna most endangered is the Southeast Asian turtle fauna: many species are being driven to extinction by the trade for food, traditional medicines, and pets. Turtles everywhere are threatened by habitat loss and the degradation of river and wetland ecosystems.

Although they are feared, crocodilians always have been valued for their skins or as food, and today more than half of the 23 species are endangered or declining. Fortunately, biologists have reversed declines in some of these species through strict legislation, research, and management programs, at least where habitat remains intact. Other species, however, are still extremely vulnerable, because human populations have encroached into their habitats to such a great extent that the crocodilians have no place left to go. Poaching remains a threat, particularly to the rarer species.

The status of squamates (lizards and snakes) generally is less well known than that of turtles and crocodilians, except for some species in commercial trade. Like other reptiles, lizards and snakes are threatened especially by habitat loss. Literally millions of these reptiles are harvested from wild populations for the fashion industry. Some species seem fairly resilient to harvest, whereas other species have declined. Collection for the pet trade and for food is also a source of concern, especially among the chameleons and the attractive and docile snakes. Harvest in certain regions, such as southeastern and eastern Asia, is likewise cause for great concern. Snakes are killed nearly everywhere, even when they pose no threats to humans. Unfortunately, little is known about the basic biology of many squamates that appear to be declining.

There are only two species of tuataras (Rhynchocephalia), both inhabitants of remote New Zealand islands. Although they are lizard-like, they are the sole survivors of an ancient reptile lineage. They are vulnerable to habitat loss, poaching, and especially the introduction of rats onto their small island homes. Both species are strictly protected, monitored, and managed.

Threats to reptiles

The threats that affect reptiles are the same as those that affect biodiversity throughout the world. The primary danger

Turtle eggs, five in each bag, are hanging for sale for about $3 in a village stall by the roadside in Terengganu, eastern Malaysia. Seaturtles have existed virtually unchanged for more than 100 million years. But human activity, including taking eggs, considered an aphrodisiac in some parts of Asia, has helped push several species to the brink of extinction. (Photograph. AP/Wide World Photos. Reproduced by permission.)

Turtle eggs, five in each bag, are hanging for sale for about $3 in a village stall by the roadside in Terengganu, eastern Malaysia. Seaturtles have existed virtually unchanged for more than 100 million years. But human activity, including taking eggs, considered an aphrodisiac in some parts of Asia, has helped push several species to the brink of extinction. (Photograph. AP/Wide World Photos. Reproduced by permission.)

to reptiles probably comes from the direct loss of habitats, whether the habitat is a small patch of temperate forest or the vast rainforest of the Amazon basin. Habitat loss is not confined to the surface of the ground but extends both arboreally and deep underground, depending on the life history requirements of the species. Migratory reptiles, such as seaturtles, face threats in different habitats, sometimes located great distances from one another, as the turtles move between natal, breeding, and feeding grounds. If a beach vital to nesting is destroyed, then the life history of the species may be disrupted, even if migratory pathways and feeding grounds are in excellent condition. Complex life cycles make species vulnerable to habitat change.

The alteration of habitats often is more subtle and less dramatic than outright habitat destruction, but it is equally devastating to reptiles. Whereas habitat destruction is immediate, the effects of habitat alteration may take place over a long time period. Thus, the difference between habitat destruction and alteration is often only a matter of scale and time. Perhaps the most common effect of habitat alteration is fragmentation of remaining habitats into smaller patches. These patches may not contain sufficient amounts of habitat to maintain a reptile population, such as a colony of tortoises or a wide-ranging population of indigo snakes. Habitat fragments may be isolated; may require animals to move (if possible) across unfamiliar ground; increase animals' vulnerability to predation and mortality from humans, especially as roads are crossed; and are more susceptible to random environmental events, such as hurricanes. Reptiles living in habitat fragments are exposed to disturbance from predators and competitors living on the edge of the fragment.

Unsustainable use, whether trade for skins, food, or pets, may devastate certain reptiles, because reproduction cannot keep pace with the loss of animals. Selective harvesting of even a portion of the population may have severe consequences. For example, female seaturtles are particularly vulnerable as they nest. They are easily captured, and the loss of this vital half of the adult population eliminates the chances of recovery. In general, little research has been undertaken on the effects of trade on reptiles, except for seaturtles and croco-dilians, because wildlife management agencies traditionally are concerned with popular and charismatic mammals and birds rather than reptiles.

Environments around the world are awash in chemicals whose effects are both direct and indirect. Pollution destroys reptile habitats by changing environmental conditions, by causing direct toxicity to an animal or its prey, or by subtle effects on reptile biophysical or physiological requirements. In contrast, long-term sublethal exposure makes reptiles more vulnerable to predators and disease. For example, such contaminants as PCBs have been shown to mimic the activity of estrogen, an important hormone that plays a part in sex determination. When these chemicals are present, abnormal development takes place, resulting in intersexes and in reduced reproductive ability (by affecting morphologic features), success, and survivorship. The populations of alligators and turtles in certain Florida lakes have declined as a result of endocrine-mimicking chemicals dumped into their habitats years ago.

There are hosts of other factors that affect reptile survivorship, including the overabundance of subsidized predators (e.g., ravens and raccoons), disease, adverse effects from nonindigenous animals and plants (e.g., mongooses, fire ants, and invasive vegetation), malicious killing, and even climate change. For example, certain predators have increased dramatically in proximity to humans. Raccoons are now without natural predators throughout much of their range, and they are subsidized by human garbage and feeding in both urban and rural areas. As their populations increase, they are capa-

Galen Rowell Corbis
Confiscated snakeskin shoe. (Photo by Galen Rowell/Corbis. Reproduced by permission.)

ble of destroying nearly every turtle nest and neonate reptile in their vicinity, and they can seriously threaten adults.

Disease (both viral and bacterial) has become a growing problem, particularly affecting seaturtles and tortoises. Disease outbreaks often are associated with polluted or environmentally stressed habitats, and pathogens may be transmitted through the release of diseased captive animals into the wild. Invasive or nonindigenous species, such as imported fire ants, directly kill reptiles and destroy eggs or modify habitats so that native species can no longer survive there. People everywhere kill harmless snakes and other reptiles for no reason at all, except pure meanness or fear.

Finally, little is known about how reptiles might respond to climate change, although it is certain that barriers between existing fragmented habitats would limit movement to new areas. In addition, global warming might have a more subtle effect. Since the temperature during egg incubation determines the sex of many reptiles, an increase in nest temperatures could produce fewer male and more female turtles and more male and fewer female crocodilians and could have a mixed result among some other species. Changes in rainfall patterns undoubtedly would affect reptiles, although increased ambient temperatures actually might benefit some species.

Conserving reptiles

The best way to conserve reptiles is to protect their habitats. This does not call solely for the creation of parks or preserves, since such areas are not isolated from the environmental effects surrounding them. Scientists realize that habitat protection is complex, bringing to bear knowledge of the interrelationships of land, water, air, and biotic components. Likewise, people surrounding protected areas must have a stake in the success of the park or preserve, because reptile conservation usually involves "people management" more than "reptile management." Additionally, there are other ways to protect habitats rather than putting them solely in public trust, as through land easements and conservation agreements, tax incentives, land banking, and private acquisition. Habitat protection must encompass the spatial needs of the species or ecosystem to be conserved, whether it is a regional landscape, a linear river or stream, or an underground aquifer.

Knowing the biotic requirements of a species helps in planning reserve design and management. There are no truly pristine areas on Earth, and all ecosystems must be managed at some level to ensure reptile survival. Management must work within the requirements of both the species and the available human resources. If either set of requirements is ignored, efforts to conserve reptiles are unlikely to succeed. Consideration of habitat restoration and manipulation, such as revitalizing ponds for bog turtles or building dens for wintering snakes, increasingly is being included in recovery and conservation plans. Both management and restoration require detailed knowledge of natural history to predict how a species will respond to change and to determine which management approaches benefit the species.

A KwaZulu-Natal Nature Conservation Service staff member cuts notches into the carapace of a loggerhead turtle hatchling (Caretta caretta) as part of a research project. (Photo by Roger De La Harpe: Gallo Images/Corbis. Reproduced by permission.)

There are several ways to curb habitat fragmentation. Planning could minimize the extent of lands affected, maximize patch size, and reduce the distances between patches. Development plans could allow for corridors between patches, protection of migratory habitats, and construction of ecopassages over or under roads and other transportation routes. For example, barrier walls and culverts have been used successfully in Florida to cut down mortality rates and to facilitate movement under a major highway across a state preserve. Deaths of alligators, turtles, and snakes declined significantly after the ecopassages were built. Effective management of habitat patches might include the removal of subsidized predators and the maintenance of natural disturbances, such as fire.

If the problem affecting reptiles leads to the loss of individuals, such as through habitat destruction or trade, legal protection is appropriate. For example, the American alligator and other crocodilians have made a remarkable comeback after legal protection and vigorous law enforcement prevented unsustainable trade. Protection of individual animals without protection of their habitat or without research designed to understand the cause of their decline will be ineffective, however, and, in some cases, counterproductive. In addition, the presence of an animal on protected lands does not mean that it is protected. For years venomous snakes were killed on sight in some U.S. national parks as part of government policy.

In many countries there are laws that restrict or curtail pollution, but pollution continues to affect ecosystems throughout the world. If reptiles are to be conserved, particularly in aquatic ecosystems, these laws must be enforced and extended vigorously. Measuring sublethal or indirect effects of chemical

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A newborn leatherback seaturtle (Dermochelys coriacea) makes its way into the ocean in Jupiter, Florida, USA. The nest produced about 200 turtles overall. If the turtle survives, it could grow to a weight of about 350 lb (158 kg); however, only about 10% of the turtles that are born each year survive to adulthood. (Phototograph. AP/World Wide Photos. Reproduced by permission.)

contamination is much more difficult, especially with the variety and number of chemicals released each year. Endocrine-mimicking chemicals have the potential to devastate wildlife populations, because they work in trace amounts. The demonstrated effects of some of these chemicals on reptiles, especially as factors affecting development, reproduction, and survival, should bring into question their impacts on humans. In addition, much research needs to be done toward understanding diseases in reptile populations, that is, their causes, the way they spread, the factors that stress immune systems, long-term effects on wild populations, and methods of treatment and management.

A few declining reptiles have benefited enormously from advances in husbandry at zoos and aquariums and even by private individuals. Zoos and aquariums serve as refugia for threatened reptiles, allowing scientists to learn much about reptile biology as a prerequisite to the restoration of wild populations. Programs for giant tortoises, crocodilians, and some of the larger lizards, in particular, hold much promise. In addition, zoos and other organizations participate in the formation of "assurance colonies," where animals seized in illegal trade are rehabilitated and held until conservation plans can be developed for their ultimate return, if possible, to natural habitats. Asian turtles currently maintained in assurance colonies offer promise that these species can be saved from extinction.

Ultimately, reptiles and the ecosystems on which they depend can be conserved only via the partnership of research, management, and public support. In this regard, education helps build appreciation for the beauty and functional value of reptiles to ecosystems, whether they control mammal pests or serve as sentinels of environmental health. The public needs to be encouraged to leave reptiles in the wild, to avoid buying products made from declining species, to refrain from keeping as pets any animals caught in the wild, and to support habitat conservation both at home and in exotic lands of wide diversity. Finally, resource managers must rely on proven management techniques, rather than opting for quick-fix "solutions" to complex problems. All conservation efforts must have a solid biological foundation so that self-sustaining and viable populations of reptiles may persist.

New tools for conservation.

At the turn of the twenty-first century exciting methods rapidly were becoming available to assist in the conservation of reptiles, including research techniques that allow for greater knowledge of natural history requirements (such as telemetry and other tracking methods), molecular biology (which helps define populations and measure diversity and re-latedness and is critical in the new field of forensic herpetol-ogy), landscape ecology (GIS technology, remote sensing and satellite imagery, all of which define large-scale distribution patterns and help scientists understand how land use affects reptiles), and new biometrical research, especially for taking inventory of communities, monitoring populations, and understanding population biology. The wealth of technological and theoretical advances makes reptile conservation a challenging and rewarding field of biology.



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