Frogs are in Big Trouble

Excerpted from mongabay.com. With more than one million unique visitors per month, Mongabay.com is one of the world's most popular environmental science and conservation news sites. The news and rainforests sections of the site are widely cited for information on tropical forests, conservation, and wildlife. http://news.mongabay.com/2007/0416-frogs.html

Chilling new evidence suggests amphibians may be in worse shape than previously thought due to climate change. Further, the findings indicate that the 70 percent decline in amphibians over the past 35 years may have been exceeded by a sharp fall in reptile populations, even in otherwise pristine Costa Rican habitats. Ominously, the new research warns that protected areas strategies for biodiversity conservation will not be enough to stave off extinction. Frogs and their relatives are in big trouble.

Writing in the Early Edition of the Proceedings of the National Academy of Sciences (PNAS), a team of researchers led by Steven M. Whitfield of Florida International University, found that amphibian and reptile populations declined by 75% since 1970 in the protected old-growth lowland rainforest of La Selva Biological Station in Costa Rica. The declines only occurred in primary forests -- neighboring abandoned cacao plantations did not suffer diminished populations.

Scientists say amphibians -- cold-blooded animals that include frogs, toads, salamanders, newts and caecilians -- are under grave threat due to climate change, pollution, and the emergence of a deadly and infectious fungal disease, which has been linked to global warming. According to the Global Amphibian Assessment, a comprehensive status assessment of the world's amphibian species, one-third of the world's 5,918 known amphibian species are classified as threatened with extinction. Further, more than 120 species have likely gone extinct since 1980. Scientists say the worldwide decline of amphibians is one of the world's most pressing environmental concerns; one that may portend greater threats to the ecological balance of the planet. Because amphibians have highly permeable skin and spend a portion of their life in water and on land, they are sensitive to environmental change and can act as the proverbial "canary in a coal mine," indicating the relative health of an ecosystem. As they die, scientists are left wondering what plant or animal group is next.

The results from the new study are particularly disturbing because they were largely unexpected. To date most observed amphibian declines have occurred in temperate regions or mountainous areas in the tropics. These have been attributed to the parasitic chytrid fungal infection, but no evidence of chytridiomycosis was found by Whitfield and his colleagues. Further, the research reports a simultaneous fall in reptile populations, a finding that has not been previously documented and suggests that something else is amiss in the ecosystem.

"The leaf litter guild of the lizard fauna represents the vertebrate group most ecologically similar to litter amphibians, and both terrestrial frogs and terrestrial lizards use similar habitats, microhabitats, and prey," the researchers write. "Because these two groups differ in physiological susceptibility to factors associated with amphibian declines (e.g., pesticide exposure or emerging infectious diseases), these ecologically similar lizards provide an invaluable contrast for sorting hypotheses about mechanisms driving amphibian declines."

Due to the pristine nature of the site, the researchers were able to dismiss a number of possible explanations for the dramatic decline in reptile and amphibian populations, including habitat modification, fragmentation, pesticides, and, of course, the deadly chytrid pathogen, since it does not affect reptiles or occur in the study area.

Instead, the researchers propose climate change is agent behind the population collapse, arguing that a reduced number of rainless days combined with rising temperatures has negatively impacted the amount of standing leaf litter, a critical microhabitat for the subject "herps."

Their results differ markedly from those in other parts of the world where documented amphibian declines have occurred suddenly, sometimes in a matter of months.

"In contrast to these sudden decline events," they write, "we demonstrate... that community-wide gradual declines also may occur."

Faring worst in the study were salamanders, which declined by an average of 14.5 percent per year since 1970. Frogs declined by 4 percent, while lizard density fell by 4.5 percent per year.

"Unfortunately, we have no idea how to explain differences in rate of decline between species," Whitfield told mongabay.com via email. "Salamanders are quite susceptible to the pathogenic chytrid fungus that has wiped out species of amphibians in the mountains, but this fungal disease can't explain all our trends. Further, aquatic species are most susceptible to this fungus, and these salamanders never enter water (they even lay eggs on land). At this point, we have way more questions than answers."