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Running Out of Reptiles
August 15, 2000
Reptile eye (crocodile?)

For more than 100 million years reptiles ruled the Earth, as dinosaurs of one type or another dominated every ecosystem on the planet. But around sixty-five million years ago the giant reptiles suffered a major setback, and the dinosaurs’ reign ended, sparing only the few species that gave rise to the lizards, snakes and turtles of today.

Now the reptiles are experiencing another spell of bad luck. According to a new report published in the journal BioScience, reptiles are experiencing a worldwide decline of cataclysmic proportions.

A sign of things to come?

"Modern reptiles are indeed going the way of the dinosaurs," says J. Whitfield Gibbons, a professor of ecology at the University of Georgia’s Savannah River Ecology Lab in Aiken, South Carolina. "[Extinction] would be the forecast if things continue the way they are." According to Gibbons, who authored the study, reptiles are dying out even faster than their distant cousins, the amphibians, whose mysterious decline has been met with global concern. There are about 270 species of reptiles on the International Union for the Conservation of Nature’s list of endangered species—three times the number of amphibian species.

The Southern Hognose Snake once thrived in the southeastern U.S., but no one has found one in the wild for the last 18 years.

Although reptiles and amphibians respond in different ways to environmental pressures that could cause them to die out, they both occupy similar habitats. The majority live in wetlands and forests, the same ecosystems that are most threatened by man. This means many of the underlying reasons for reptile and amphibian decline are the same, according to Gibbons. Moreover, because reptiles and amphibians are more sensitive to disturbance than other groups of animals, they could be pointing toward a larger trend: "They are an indicator of our environmental condition, and that’s reason to be concerned," Gibbons says. "If the amphibians are disappearing, if the reptiles are disappearing, who’s next?"

Climate change, habitat loss, exploitation by humans, pollution and disease are just some of the reasons behind the decline [see page 2 of this article]. Crocodiles, alligators and turtles are particularly sensitive to climate change because, by a quirk of evolution, the sex of their offspring is determined by the temperature at which their eggs incubate. Sudden changes in global temperature could cause a massive increase in numbers of one sex and a decrease in the other, causing a crash in their population. This mechanism was even proposed as one of the possible reasons for the dinosaurs dying out.

Gibbons says that exploitation of reptiles by humans is another serious threat to their future. "An excellent example is the leatherback sea turtle," he notes. "In 1980, 115,000 leatherback sea turtles nested on beaches around the world.... In 1995 there were only 35,500." The reason for their decline is the demand for sea turtle eggs and meat, which is easy to harvest from beaches where the adult turtles congregate to mate and lay eggs.

A call to action

Alligator or crocodile

Yet not enough is known about reptiles and how they interact with the environment to be certain of what’s causing their decline. "There are many threats to reptiles that are obvious... but there are mysteries also," says Gibbons. "Mysteries and potential threats that we haven’t done the studies to know." One example is the impact of this summer’s wildfires in the western U.S. on reptiles. He says the fires possibly contribute to the decline, "[but] the studies haven’t been done." In fact, the connection between human exploitation of leatherback turtles and their massive decline only came to light, says Gibbons, because of three large studies of the giant reptiles.

Gibbons says the purpose of his recent paper is to highlight the problem, but that is only the beginning: "We don’t have to lose our reptiles. We can prevent the loss of reptiles around the world by first identifying the problem—that’s been done—then communicating this problem to the scientific community and the general public."

But even then, much more will have to be done to stem the disappearance of the reptiles, one of which is a shift in opinion "We’re in the driver’s seat, humans are," says Gibbons. "We’re the ones who have to make sure that our actions aren’t detrimental to these other organisms. This is not a new message, but I think the reptiles are showing that it’s happening everywhere."

Why are they dying?

Just like the reasons for amphibian decline, the global trends that are causing reptiles to disappear are complex and interconnected. Here are some of the main contributing factors outlined in the new study.


Habitat Loss and Degradation - Possibly the main contributing factor to the decline, wetlands and woodlands are especially vulnerable. The disappearance of bogs in the eastern United States has led to a decline in bog turtles. Loss of 97 percent of the southeastern longleaf pine forest has put the eastern indigo snake on the endangered list.

Introduced Invasive Species - The introduction of rats and pigs to the Galapagos Islands has led to the near extinction of the giant Galapagos tortoise. These animals eat the tortoises eggs and compete with them for food.

Environmental Pollution - Wetlands are particularly vulnerable to pollution carried in runoff water. Male American alligators in lake Apopka, Florida have been found to have low testosterone levels and deformed reproductive organs due to chemical contamination in the water.

Disease - Environmental factors like changes in habitat, climate and pollution are thought known to make many animals more susceptible to disease. A bacterial upper respiratory tract infection is thought to be responsible for declines of desert tortoises in the southwest and gopher tortoises in the southeast United States.

Unsustainable Use/Exploitation - As well as sea turtles fresh water turtles are also threatened. A recent report finds that most turtles in Vietnam and southern China are endangered and that turtles can no longer be found in the wild in Vietnam, they have been collected to satisfy China’s insatiable appetite for turtle meat.

Southern Hognose Snake (close-up)

Global Climate Change - Changes in habitat resulting from significant climate change would impact reptile populations the most. Because reptiles do not disperse rapidly, unlike many mammals and birds, they may be unable to move with shifting habitat as the world warms up.

Mysteries - Many reptiles are disappearing for no apparent reason. The southern hognose snake (above, right) has not been seen in it’s native Alabama and Mississippi for more than 18 years even though large areas of it’s habitat remain untouched by man. Only by studying long tem changes in reptile populations can such mysteries be solved, says the report.

Elsewhere on the web:

Partners in Reptile & Amphian Conservation

Society for the Study of Amphibians and Reptiles

Conservation International

Canadian Amphibian and Reptile Conservation Network

A Guide to Amphibian and Reptile Conservation

TRAFFIC—Policing trade in endangered species

by Tom Clarke

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