ENHS Nature Trails January 2001 Article 2

Natural History and You - The President's Forum
by Nathan Tublitz

The Decline of Amphibians: A Global Ecological Emergency in Progress

Most school children know that amphibians are a class of vertebrates that include frogs, salamanders and caecilians, that they have been on earth since before the dinosaurs, and live in an amazing variety of habitats such as wetlands, forests, savannas, deserts, agricultural landscapes and cities. What they have not been told is that amphibian populations throughout the world are declining. Perhaps someone should tell them since they know the solution.

Concern for diminishing amphibian numbers first surfaced in 1989 at the World Congress of Herpetology, where several papers were presented and informal discussions were held. Subsequent studies throughout the 1990s continued to document this alarming trend in many diverse locations. In Yosemite Park, 5 of 7 frog and toad species suffered serious declines in the 1990s and two other species completely disappeared from the Park. The golden toad of Costa Rica, named because of the male's bright orange color during the breeding season, was seen in high numbers throughout the 1970s and early 1980s but suffered a drastic decline in the late 80s, with 1500 counted in 1987, 11 in 1988, and only one in 1989. Since then not a single individual has been observed and the species is now believed to be extinct. The small, gastric brooding frog of Australia, so called because it swallows and broods its young in its stomach, was only discovered in 1972 but the frog has not been seen since 1981.

Amphibian declines such as these have been documented on every continent except for Antarctica (which has no extant amphibian species), leading to speculation that there is a global cause for this distressing problem. Many causes such as global warming, thinning of the ozone layer, and deadly new diseases have been postulated. Although the jury is still out on many of these, several causes have been unequivocally identified:

1. HABITAT DESTRUCTION. The single, most obvious threat to amphibians comes from the loss and fragmentation of wetland and forest habitats. The clearing of forests for paper and agricultural needs and the draining of wetlands for urban and suburban development are one-way processes; these losses are, with few exceptions, permanent once completed. Of the original Willamette Valley wetlands documented to have been in existence prior to the 19th C Lewis and Clark expeditions, 99% have been drained. Habitat loss this rapid occurs too quickly for amphibian species to adapt and survive.

2. INTERNATIONAL DEMAND. The emerging global marketplace is fostering an unprecedented demand for amphibian products. Amphibians are valued as pets, food, medicine, research subjects, souvenirs and aphrodisiacs. Although some are raised in captivity, most are not and thus are harvested and removed from their native habitats. The US ranks #1 in terms of importing live amphibians. Sadly, inhumane transport and holding conditions lead to the unnecessary loss of huge numbers of amphibians.

3. POISONING. An unusual amphibian adaptation is their porous skin, which allows direct transport across the skin of water, oxygen and other essential, water-soluble nutrients without ingestion. However, the porous nature of amphibian skin also allows the entry of harmful chemicals. The favorite habitat of amphibians, wetlands, because of its intermediary location between upland regions and rivers, is the inevitable repository for everything that flows downhill. Oils, gasoline and other petroleum-derived products from motor vehicles and roads, toxic waste products from industrial and commercial sites, pesticides and herbicides used in modern agriculture practices as well as a broad range of chemicals used in every day life, all find their way into our wetlands and contaminate amphibian habitats. Pollution levels in our own Willamette River, once a sparkling gem, have risen so high that they are causing deformations in local frogs and amphibians, resulting in the river being listed as one of the 10 most polluted rivers in the US.

4. INTRODUCTION OF NON-NATIVE PREDATORS. There is strong evidence that the introduction of non-native predators are responsible for the decline of some amphibian populations. Fish, crayfish and bullfrogs, introduced for commercial and recreational purposes, have wreaked havoc on native amphibian species. In the southern Willamette Valley, bullfrogs have outcompeted native red-legged frogs to the brink of extinction.

5. ATMOSPHERIC CHANGES. Ultraviolet radiation from the sun (UV-B) is increasingly passing through our atmosphere as the ozone layer is thinning. Several studies have shown that this increased UV-B radiation is causing deleterious effects on the eggs and young larvae of several Cascade mountain frog species, leading to reproductive infertility. Shifts in climate due to global warming, causing drier and warmer conditions, have been implicated in the disappearance of several Costa Rican cloud forest frog species.

6. DISEASES. Over the past 10 years there have been documented reports of mass deaths of amphibians across the world. Pathogens such as bacteria, viruses, fungi, and fungal-like algae, have been demonstrated to be the ultimate cause of death but the stress factors that made these amphibians susceptible are unknown. Many pathogens are transmitted by introduced fish and other aquatic organisms. Amphibian diseases are also spread by people and livestock that unknowingly carry microscopic aquatic species.

The world-wide decline in amphibian populations is likely to be a harbinger of more ominous news: that humans are wreaking global ecological havoc. With respect to amphibians we fortunately have not yet reached the point of no return and can still reverse this trend. How? Pressure government officials to appropriate more funds to preserve wetland and forest habitats. Monitor regional amphibian populations more closely with scientifically accurate procedures. Provide research into amphibian population dynamics and environmental factors that affect amphibian growth and development. Regulate use of pesticides, herbicides and other known toxins affecting amphibian populations. Most importantly, communicate the need for conserving populations, species and ecosystems that are being degraded by humans and their activities. Kids intuitively understand that for an individual and a species to survive, it needs clean water, untrammeled habitats, and sufficient food. Perhaps it is time that we adults start listening to our children about saving our earth.

For more information on the world-wide amphibian decline, go to

www.usgs.gov/amphibian_images.html
www.frogweb.gov/tadd/publications.html

Nathan Tublitz
Professor of Biology
Institute of Neuroscience
University of Oregon
Eugene OR 97403
Phone: 1-541-346-4510 FAX: 1-541-346-4548

[ Back ]

Page last modified: 15 April 2001
Location: http://biology.uoregon.edu/enhs/archive/jan01/jan012.html
E-mail the WebSpinner: cpapke@gmail.com