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Costa Rica’s Harlequin Frog, once thought extict, florishes on the Rainmaker Reserve.

Costa Rica Frog

It has been suspected for some time that global warming may cause widespread amphibian extinctions. In a study published in 2006 by J. Alan Pounds suggested that Costa Rica Frogmany harlequin frog species (Atelopus) across Central and South America have disappeared due to deadly infectious diseases spurred by changing water and air temperatures.

At one time the Harlequin Frog (actually a toad) was thought to be extinct. In 2003 the Harlequin Frog was rediscovered in the primary rain forest of the Rainmaker Reserve on the Central Pacific Coast of Costa Rica.

“Disease is the bullet killing frogs, but climate change is pulling the trigger,” said Pounds, lead study author and resident scientist at Costa Rica’s Monteverde Cloud Forest Preserve.

“Global warming is wreaking havoc on amphibians and will cause staggering losses of biodiversity if we don’t do something fast.”

Costa Rica VacationThe World Conservation Union (IUCN) has listed this frog as Critically Endangered and facing an extremely high risk of extinction in the wild, because most of them have disappeared since 1988. In 1996, in fact, scientists feared that all of the more than one hundred populations known to exist in Costa Rica were already gone. Seven years later, however, a tiny population was discovered at Rainmaker Reserve.

About two-thirds of the 110 known harlequin frog species are believed to have vanished during the 1980s and 1990s. The primary culprit, Pounds suggests, is the disease-causing chytrid fungus Batrachochytrium dendrobatidis.

Amphibian skin is extremely thin, which makes frogs acutely sensitive to even minor changes in temperature, humidity, and air or water quality. It also makes frogs more susceptible to chytrid fungus.

Costa Rica FrogThe new study suggests that temperature extremes may have previously helped keep the deadly disease in check. But new climate cycles are now moderating those annual temperature swings.

Global warming has increased evaporation in the tropical mountains of the Americas, which in turn has promoted cloud formation, the study reports. That cloud cover may have actually decreased daytime temperatures by blocking sunlight. At the same time, it may have served as an insulating blanket to raise nighttime highs.

Pounds believes the combination has created ideal conditions for the spread of the frog-killing fungus, which grows and reproduces best at temperatures between 63° and 77°F (17° and 25°C).

Related Article about Rainmaker Reserve.

Related Article About Amphibians in Costa Rica

Harlequin Frogs True Toads and Relatives: Bufonidae – Harlequin Frog (atelopus Varius): Species Accounts

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Why are Amphibians in Decline?

Wednesday September 5, 2007

In recent years, scientists and conservationists have been working to raise public awareness of a global decline in amphibian populations. Herpetologists first started noting that amphibian populations were falling at many of their study sites in the 1980s. Those early reports were anecdotal and many experts doubted that the observed declines were cause for concern (the argument was that populations of amphibians fluctuate over time and the decline could have been merely natural variation).

But by 1990, a significant global trend had emerged—one that overstepped normal population fluctuations. Herpetologists and conservationists started voicing their concern for the worldwide fate of amphibians. Their message was alarming: of the estimated 5,918 known species of amphibians that inhabit our planet, a staggering 1,856 species were listed as endangered, threatened or vulnerable on the IUCN Red List (Global Amphibian Assessment 2007).

Amphibians are considered to be indicator species for environmental health: they have delicate skin that readily absorbs toxins from their environment; they have few defenses and can fall prey to non-native predators; they rely on both aquatic and terrestrial habitats at various times during their life cycle. If amphibians populations are in decline, it is likely that the quality of the habitat in which they live is suffering.

There are numerous known factors that contribute to amphibian declines—habitat destruction, pollution, the effects of introduced species. Yet research has revealed that even in pristine habitats—those that lie beyond the reach of the bulldozer and crop-duster—amphibians are disappearing at a shocking rate and without explanation. Scientists are now looking to global phenomena for explanations. Climate change, emerging diseases, and increased exposure to UV-B radiation (due to ozone depletion) are all additional factors that could be contributing to falling amphibian populations.

So it seems the question ‘Why are amphibians in decline?’ has no simple answer. Instead, amphibians are disappearing due to a complex mixture of factors which include:

  1. Alien Species—Native amphibian populations can suffer decline when alien species are introduced into their habitats. There are a number of ways an introduced species can impact populations of native amphibians. For instance, an amphibian species may become the prey of the introduced species. Alternatively, the introduced species may compete for the same resources required by the native amphibian. It is also possible that the introduced species may form hybrids with the native species and in doing so reduce the prevalence of the native amphibian within the resulting gene pool.
  2. Over-Exploitation—Amphibian populations in some parts of the world suffer decline because they are captured for the pet trade or are harvested for human consumption.
  3. Habitat Alteration and Destruction—Alteration and destruction of habitat has devastating effects on many organisms and amphibians are no exception. Changes to water drainage, vegetation structure, and habitat composition all impact the ability of amphibians to survive and reproduce. For example, the drainage of wetland areas for agricultural use of the land directly reduces the habitat available for amphibians which require aquatic habitat for breeding and foraging.
  4. Global Changes (Climate, UV-B, and Atmospheric Changes)—Global climate change presents a serious threat to amphibians because altered precipitation patterns will likely result in changes to wetland habitat on which amphibians rely. Additionally, increases in UV-B radiation due to ozone depletion have been found to severely impact some species of amphibians.
  5. Infectious Diseases—Significant amphibian declines have been associated with infectious diseases such as chytrid fungus and iridoviruses. Chytrid fungal infections in amphibians was first discovered in populations of amphibians in Austrailia but also has been found in Central America and North America.
  6. Pesticides and Toxins—The widespread use of pesticides, herbicides, and other synthetic chemicals and pollutants has severely impacted many amphibian populations. In 2006, scientists at the University of California, Berkeley found that mixtures of pesticides were causing amphibian deformities, reducing reproductive success, harming development, and increasing susceptability to diseases such as bacterial meningitis.

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