Death by Rubber

Of the three most common amphibian species in northern Yellowstone, the blotched tiger salamander population has fallen by half, while spotted and chorus frog populations have decreased by 68 and 75 percent respectively since the early 1990s, according to McMenamin’s study, which was published in the Proceedings of the National Academy of Sciences in November 2008.

“We’re putting a lot of resources into protecting the natural populations in Yellowstone, but we are looking at trends here that are larger than what we can directly prevent,” McMenamin says. The link between population declines and large-scale climate problems with no easy fix doesn’t bode well for global amphibian populations, she adds.

Though amphibian declines are an issue worldwide, the tropics, which have the greatest amphibian biodiversity, may stand to lose the most species due to habitat destruction, climate change and disease. Brazil alone is home to 811 amphibians, nearly 13 percent of all the known amphibian species in the world. There are many ecological niches to fill in the rainforest and amphibians have found their way into most of them — from underground to the high rainforest canopy.

Because tropical amphibian species occupy very specific rainforest niches, the diversity of species is great, but the population of each species may be relatively small, making these species particularly vulnerable. The most immediate threat in the tropics is a mysterious fungal disease, known as chytridiomycosis, that is devastating amphibian populations in Central and South America. David Wake, the Berkley herpetologist, studies amphibians in the Monteverde Rainforest Reserve in Costa Rica. “You used to hear the frogs by day and night in the forest and now there’s silence. Fifty percent of the amphibian species are gone,” he says. Wake believes the cause of the drastic decline is the killer fungal disease, but also says its impact has been compounded by habitat loss and climate change — stresses that can reduce a species’ ability to cope with disease.

No amphibian species seems to be safe from chytridiomycosis, which can infect both tadpoles and adults. While it does not kill the tadpoles, they die soon after metamorphosis. It attacks the keratin — a protein in the animal’s skin — causing the skin to become hard and thick. Because amphibians normally exchange oxygen and other ions through the skin as well as lungs, the disease eventually suffocates them.

So far, there is only anecdotal evidence of how the worldwide decline of amphibians is affecting the larger ecosystems in which they live. No one can accurately predict what the collapse of frog or salamander populations will have on other plant or animal species in the future — ecosystems are too massive, and the biological relationships between different groups of organisms too intricate. What is indisputable, though, is that many animals depend on amphibians for food. They are the forest’s unseen biomass.

Scott Connelly, an ecologist at the University of Georgia, is one of the few scientists who has tried to assess how ecosystems change when amphibians are wiped out. Connelly was studying how tadpole feeding affects algae in a small stream in Panama when chytridiomycosis swept through the forest, leaving virtually no amphibians behind. After the die-off, the amount of algae in the stream increased noticeably. Connelly is unsure what this finding means for the future. “Evolutionary changes over thousands of years are where the action is going to be,” he says. “The cascade effects from these changes will take time to see.”

Back in New Jersey, the volunteers conducting the state amphibian survey know what their tiny charges are up against — in the Garden State and around the world. Compared to the enormous threats of disease, climate change and habitat destruction facing amphibians, the modest efforts of a small group of volunteers helping frogs and salamanders cross a rural road seems almost pointless. Even if they save hundreds tonight, the effort would be a drop in the bucket compared to worldwide losses. And on this night, it doesn’t look like they will save any at all: The rain is not falling and the frogs and salamanders are nowhere to be seen.

Even so, the frog-counters soldier on, hopeful that they can have an impact, at least on a small scale. Nancy Schiesl and her husband live down the street. They see their involvement with the amphibian survey over the last seven years as a form of community service, making their neighborhood a better place to live — for all species. “We believe we’re making a difference,” says Schiesl. “One car kills so many. We love to have them here, love to hear the sound of the frogs at night.”

A misty rain begins to fall, barely perceptible at first, then driving harder. A volunteer’s flashlight beam exposes a single spotted salamander edging slowly onto the shoulder. The volunteers let out triumphant whoops and rally around the lone migrant as it struggles against the friction of the road, inching slowly toward the other side.

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