English

In the past three decades, declines in populations of amphibians (the class of organisms that includes frogs, toads, salamanders, newts, and caecilians) have occurred worldwide. In 2004, the results were published of the first worldwide assessment of amphibian populations, the Global Amphibian Assessment. This found that 32% of species were globally threatened, at least 43% were experiencing some form of population decrease, and that between 9 and 122 species have become extinct since 1980. As of 2010, the IUCN Red List, which incorporates the Global Amphibian Assessment and subsequent updates, lists 486 amphibian species as "Critically Endangered". Experimental studies have shown that exposure to commonly used herbicides such as glyphosate (Tradename Roundup) or insecticides such as malathion or carbaryl greatly increase mortality of tadpoles. Additional studies have indicated that terrestrial adult stages of amphibians are also susceptible to non-active ingredients in Roundup, particularly POEA, which is a surfactant. Atrazine has been shown to cause male tadpoles of African clawed frogs to become hermaphroditic with development of both male and female organs. Such feminization has been reported in many parts of the world. While most pesticide effects are likely to be local and restricted to areas near agriculture, there is evidence from the Sierra Nevada mountains of the western United States that pesticides are traveling long distances into pristine areas, including Yosemite National Park in California.

Amphibians are sensitive to most classes of pesticides including insecticides, fungicides, and herbicides. Adult and juvenile amphibians are exposed to pesticides on land through aerial sprays for mosquitoes, forestry and agricultural pests, drift, and dermal absorption from soil and plants. Because the EPA does not require amphibian toxicity tests for pesticide registration, there are large data gaps. These data gaps are being closed by independent scientists. One experiment tested label spray rates of 7 pesticides on adults of the common frog species, Rana temporaria. Mortality ranged from 40-100%. Perhaps most surprising was the lethal effects of fungicides. Two fungicides caused 100% mortality within one hour, others showed 40-60% mortality. Three products caused 40% mortality after 7 days after 10% label rate exposure (Bruhl et al. 2013). Direct oversprayingof terrestrial life stages of several frog species with Roundup at label rates resulted in an average 79% mortality. Van Meter et al. (2014) tested pesticide absorption from soil with 5 pesticides and 7 adult frog species. Atrazine showed highest absorption and bioaccumulation, although skins were generally more permeable to fipronil. Water solubility and soil partition coefficients were good predictors of dermal absorption. Maximum label rates were applied to soil, and resulting tissue concentrations ranged from 0.019 to 14.6 µg/g (ppm) over an 8 hour period. Immune suppression can occur at tissue concentrations 300-7300 times lower.

Things aren’t looking good for reptiles and amphibians lately, especially frogs. John Alroy at Macquarie University in Australia published a study last month examining recent extinctions for the two groups of animals, and the results are alarming. “About 200 frog extinctions have occurred and hundreds more [frog species] will be lost over the next century, so we are on pace to create a mass extinction,” according to the study. Alroy chose to study reptiles and amphibians partly because “there was a large amount of global data available for these groups, and partly because of a growing concern in the scientific community over the health of frog populations, which are thought to be in a state of decline in many places,” says the Washington Post. Alroy also looked at salamanders, snakes and lizards, but “he found that frogs seemed to be the most vulnerable to extinction—the results suggested that more than 3 percent of all frog species have disappeared, largely since the 1970s,” according to the Washington Post. The findings are especially alarming because the research method known as a Bayesian approach is “highly conservative,” meaning that the estimated number of past and future frog extinctions could, in fact, be even higher.

There is broad concern that a mass extinction of amphibians and reptiles is now underway. Here I apply an extremely conservative Bayesian method to estimate the number of recent amphibian and squamate extinctions in nine important tropical and subtropical regions. The data stem from a combination of museum collection databases and published site surveys. The method computes an extinction probability for each species by considering its sighting frequency and last sighting date. It infers hardly any extinction when collection dates are randomized and it provides underestimates when artificial extinction events are imposed. The method also appears to be insensitive to trends in sampling; therefore, the counts it provides are absolute minimums. Extinctions or severe population crashes have accumulated steadily since the 1970s and 1980s, and at least 3.1% of frog species have already disappeared. Based on these data and this conservative method, the best estimate of the global grand total is roughly 200 extinctions. Consistent with previous results, frog losses are heavy in Latin America, which has been greatly affected by the pathogenic chytrid fungus Batrachochytrium dendrobatidis. Extinction rates are now four orders-of-magnitude higher than background, and at least another 6.9% of all frog species may be lost within the next century, even if there is no acceleration in the growth of environmental threats.