What's the Fuss About Frogs?

Now you see them. Now you don't. Such is the game frogs seem to be playing with herpetologists (scientists who study amphibians) worldwide. Except that this game is not fun.

The gastric brooding frog, for example, was first discovered in 1973 in a small area of the Australian rain forest. “The frog had the most amazing method of reproduction,” says James Hanken, professor of herpetology at Harvard University in Cambridge, MA. After mating, the female ate her fertilized eggs and incubated as many as 25 young in her stomach. After several weeks, she burped or vomited up tiny, fully formed frogs.

Although the brooding frogs were never very common, scientists could always locate them. Then, about 1981, the species completely disappeared. “People don't know what happened, to this day,” says Hanken. “Some people suspect that it may have been the result of a disease, but no one knows for sure.”

Mysterious disappearing-frog stories like this are being heard all over the world. But not just frogs are disappearing: All forms of amphibians are on the decline, including toads, newts, salamanders, and a legless variety known as caecilians.

Canary in the Environmental Coal Mine

Amphibians occupy an important position in the community ecology for many reasons, says Hanken. First, they are a significant food source for other vertebrates such as snakes, birds, and small mammals. Plus, they eat insects such as mosquitoes, providing a natural pest control.

Amphibians also slow the greenhouse effect by eating the insects that normally contribute to decomposition of the forest floor, says Dr. Richard Wyman, executive director of the Edmund Niles Huyck Preserve and Biological Research Station in Rensselaerville, NY.

But perhaps the biggest reason for paying attention is that they are the canary in the ecological coal mine, says Wyman. Coal miners used to carry canaries into the mines to warn of poison gases or lack of oxygen. If a canary died, then the men knew that they had to get out quickly.

Amphibians are the environment's warning signal. They are great indicators of what is going on in ponds, forests, the soil, and even the air, says Wyman. Many live their lives on both water and land and are more sensitive to the degradation of their environment than other animals because of their thin, porous skin, which absorbs pollutants directly into their bodies. “They are tipping us off that we are starting to poison our environment,” says Hanken. “Ultimately, these poisons will affect other organisms, including humans, as well.”

Scientific Detective Work

To assess the problem, the World Conservation Union organized the Declining Amphibian Populations Task Force (DAPTF) in 1991. This international SWAT team of 3,000 scientists has more than 100 working groups located in 90 countries. For ten years, these scientists sought answers to: Are amphibians really declining? If so, to what extent? What is causing the decline? What can we do about it?

“We have both good news and bad news,” says Hanken. “The good news is that we know much more than we did about amphibians all over the world, and what is causing the decline. The bad news is that the problem is a lot worse than we expected. In fact, many more species are declining than we originally suspected, including those that were once abundant and common.”

Hanken predicts that between one-third and two-thirds of the world's species of amphibians are on the decline. Several went extinct within just the last few decades.

A Polluted Mixture

Several of the causes for decline identified by biologists include climate change, habitat deforestation, pesticides, disease, and introduced species.

Unfortunately, few of these factors act alone. Several combined simultaneously can devastate a specific amphibian, such as in the case of the golden toad of Costa Rica.

“This was such a spectacular species,” says Hanken, “that they were the symbol for the country.” The males were flaming golden orange. The female ranged in color from dark olive to black with splotches of bright red edged in yellow. “During breeding season, hundreds of toads gathered around pools deep in the cloud forest,” Hanken continues. Then, one year in the late 1980s, herpetologist Martha Crump was able to find only two frogs throughout the whole park. The next year, she found none. As in the case of the gastric brooding frog, their disappearance is also a mystery, because nothing obvious appears to have been wrong.

After years of studying the problem, scientists have a theory. They found that the rainfall pattern changed right around the time of the frogs' disappearance, says Hanken. Due to deforestation, global warming, and El Niño, the amount of rainfall, clouds, and humidity declined drastically. “When we talk about global warming, we are talking about only a fraction of a degree over a year,” says Hanken, “but this is still enough to change local climate.”

A Success Story

Once biologists know the cause, sometimes they are able to find solutions. Over the years, California Fish and Game (CF&G) stocked the high-altitude lakes in the Sierra Nevada Mountains with trout. Trout don't normally live here, because these lakes are too cold for the fish to breed. But every spring, CF&G flies over and drops the trout from planes for local and touring anglers to fish. “We found a tight correlation between amphibian decline and released trout,” says Hanken, because the fish eat the frog eggs as well as tadpoles.

So CF&G, along with the U.S. Park Service, started a scientific pilot study to stop stocking certain high-altitude lakes and see what would happen. In some lakes, anglers even removed all of the trout. The result? The frogs are coming back!

“In this case, the problem was easily discovered and reversed,” says Hanken.

For more difficult situations, researchers are breeding endangered frogs in captivity. The Detroit Zoo in Michigan set up a special facility just for this purpose. “If we can maintain a population of amphibians in captivity, then perhaps in the future, when their habitat has been stabilized, we can reintroduce them into the wild,” says Hanken.

You Can Help

There are so many different types of amphibians in the world that biologists can't monitor them all. If you want to help, Hanken suggests getting involved with the amphibian census. People can join the North American Amphibian Monitoring Project (NAAMP) and volunteer to listen to frogs during the breeding season. “We want to count the number of sites, or ponds where we hear the frogs calling during mating, and try to determine how many frogs there are,” Hanken says.

Volunteers help herpetologists identify the type and number of frogs and toads in an area, determine if the amphibians are breeding, and try to gauge what is happening to that population from year to year. From this information, scientists are alerted to changes in numbers. If there is a decline, they will try to determine the cause and, hopefully, stop or reverse the process.

By conserving natural resources, we slow global warming, which in turn may stop and even reverse this decline. With help from us all, maybe the herpetologists of tomorrow can play “Now you see them” for fun.

Hopping Out of Sight

Amphibians have survived on our planet for more than 300 million years due to their amazing ability to adapt to their environment. However, even Mother Nature can't keep up with all the changes created by humankind. Here's a look at a few amazing frogs that just couldn't adjust.

Vegas Valley Leopard Frog
(Rana fisheri)

This olive-green frog with yellow back legs was the first frog known to go extinct. It was last seen in the wild in 1942. The two- to three-inch-long (5 to 7.5 cm) amphibian lived in the Las Vegas Valley in Nevada. Herpetologists believe that in addition to eating insects and spiders, they also ate fish and their own young. As the city of Las Vegas grew, water was needed to supply the continuous influx of people. Officials capped local springs and pumped groundwater to the city, totally destroying the frog's habitat.

Israel Painted Frog
(Discoglossus nigriventer)

Very little is known about this two-inch-long (5 cm) frog that disappeared in 1955. Its back was a colorful combination of ocher (yellow-brown), rust, gray, and black. Small white spots dappled its dark belly. It lived in northern Israel and possibly adjacent parts of Syria. Herpetologists believe that it went extinct because so much of its wetland habitat was drained in an effort to produce farmland for a growing population.

Mountain Mist Frog
(Litoria nyakalensis)

The last mountain mist frog was seen in the wild in 1990. The two-inch-long (5 cm) amphibian lived in northeastern Queensland, Australia. The frogs sported large discs on their toes so that they could perch on rocks or low vegetation hanging over fast-flowing streams. The tadpoles had large, suction-like mouths that allowed them to cling to rocks in swift water. The reason for their extinction is unknown.

Rancho Grande Harlequin Frog
(Atelopus cruciger)

This one- to two-inch-long (2.5 to 5 cm) frog was once so abundant in northern Venezuela that at certain times of the year, scientists could collect hundreds in just an hour. Cruciger comes from the Latin word crux, meaning cross. The frog boasted a dark cross on its yellowish-green head, shoulders, and back. Because of its poisonous skin, it had no known predators except for a nonvenomous snake, which was immune to the neurotoxins in the frogs' hide. Due to climate change and pollution, all were gone by 1982.

Golden Coqui
(Eleutherodactylus jasperi)

The skin on this pale yellow frog's belly was so thin that you could watch its heart pump. It was less than an inch (2.5 cm) in length, and lived in the bromeliads or tropical plants of Puerto Rico. The golden coqui was the only New World frog known to produce live young instead of laying eggs. Unlike common frogs that must grow from tadpoles into adult frogs, these young resembled the adults from birth. The last one was seen in the wild in 1981. Herpetologists blame their disappearance on a number of factors, including loss of habitat, acid rain, overharvesting (killing frogs for food, hides, pets, and research), and their low reproductive rate.

Why Should We Care?

If you still aren't sure whether amphibians actually benefit people, listen to what happened in India. In the early 1980s, India and Bangladesh routinely harvested frogs and sent them to the United States, where Americans consumed more than 6.5 million pounds of frog legs annually. That meant killing hundreds of millions of frogs a year. Ninety percent of this total came from these two countries alone. As a result of fewer frogs, the mosquito population became unbearable. Cases of malaria (a disease carried by mosquitoes) ballooned, along with the need for pesticides. Eventually, both India and Bangladesh were forced to ban frog exports.

Deformed Frogs: Natural or Human-made?

Deformed frogs are a small aspect of the overall amphibian decline. Sightings of abnormal frogs appear to be on the increase since they were first reported in 1995 by a group of middle school students from southern Minnesota. Students found frogs with extra or missing legs, eyes, or digits, or with malformed jaws. But scientists are not sure if this is a natural or unnatural phenomenon.

“Deformed frogs are only the size of my pinky,” says herpetologist Richard Wyman. “And they won't grow much bigger. They will be eaten first. A frog with an extra leg, for example, can only hop in circles. It doesn't have a prayer of escaping its predators.”

The exact cause of the malformations is still subject to debate. According to researchers from the U.S. Geological Survey, there are three popular theories: a parasite; pesticides and herbicides; or damage caused by ultraviolet light.

Wyman isn't even positive as to whether deformed frogs are really on the increase. “There have always been deformed toadlets and froglets,” he says. Citing of abnormal frogs appeared in museum records as early as 1870. This was well before the development of insecticides or pesticides. “Once these frogs were discovered, people paid much more attention to tadpoles, thereby noticing them more.”

Despite differences of opinion, there is one thing on which everyone can agree: More work is needed to understand what is truly going on.


Causes for Amphibian Decline

To date, herpetologists have identified eight primary reasons:

Pesticides and herbicides:
Chemicals used on lawns and agricultural farms to control insects poison amphibians.
Global warming:
The warming of the Earth's atmosphere affects the climate through decreased rainfall or increased temperatures.
Habitat destruction:
The filling in of wetlands and the tearing down of forests destroys animals' homes and breeding grounds.
Habitat fragmentation:
Roads, parking lots, and other obstructions prevent amphibians from moving freely throughout their habitat.
Introduced species:
Animals that are released in an area where they did not exist before eat amphibians and their eggs, young, and prey.
UV light:
The thinning of the ozone layer allows more harmful ultraviolet light from the sun to reach Earth, where it damages amphibian eggs.
New diseases:
A fungus discovered just 3 or 4 years ago is causing amphibians to die all over the world. But it isn't clear whether these pathogens are the primary cause, or if the amphibians were weakened by something else and then became susceptible to the disease.
Acid rain:
Acid rain caused by industrial air pollution damages soil and water and kills embryos of species that breed in lakes and ponds.

Vocabulary

correlation:
A causal relationship between two things.

ecological:
Relating to the science that deals with the relationships among organisms and between organisms and their environment.

El Niño:
A warming of the ocean surface off the western coast of South America that occurs every 4 to 12 years.

extinct:
No longer existing in living form.

pollutants:
A substance that makes an area dirty or impure.

porous:
Full of tiny openings through which liquids and gases may pass.

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Activity

  1. Why do you think it is important to understand why a species might be declining? Write a few sentences explaining your answer.
    [anno: Answers will vary but could include that we may not know that something is wrong in the environment until a particular species is studied. When the declining species is studied, and the cause of its decline is identified, then we know more about what is happening in an environment.]