Thousands of Kihansi spray toads, all less than an inch long, once thrived in the Kihansi River gorge in Tanzania. Harnessing energy from this Global Diversity Hotspot’s waterfalls, the Tanzanian government and the World Bank built a dam there in the 1990s. The dam, in turn, brought the species to the brink by drying out their wetland habitat. As their population dwindled in 2000, the Wildlife Conservation Society (WCS) brought 500 toads to the Bronx Zoo in New York, and others to Ohio’s Toledo Zoo. Now, these captive toads are the only survivors of their species. Once the chytrid skin fungus spread to the Kihansi gorge, the species became extinct in the wild. Thanks to the zoos" sanctuaries, however, their numbers are steadily growing.
The Bronx Zoo is taking part in 2008’s Year of the Frog, an awareness and fundraising campaign organized by the international program, the Amphibian Ark formed by The World Conservation Union’s Conservation Breeding Specialist Group and Amphibian Specialist Group, along with the World Association of Zoos and Animals (WAZA).
The purpose of the Amphibian Ark is to save endangered species by establishing ex situ (off-site) breeding colonies in zoos, botanical gardens, and aquariums. This intervention is necessary for some species, since lab-type environments are far more controlled than those within nature. If the program succeeds, 500 of WAZA’s largest zoos will take responsibility for one species, thereby providing a stopgap measure to stabilize and protect populations. The global zoo community, however, seems primed to care for only 10 percent of those species. In order to build supplementary facilities, conduct research, and restore populations, the Amphibian Ark has estimated that it will need $400 million in funding. The group emphasizes that this is a short-term solution, however; the long-term goal is to restore the animals" habitats and release them back to the wild.
With amphibian populations decreasing rapidly, the need to counter recent threats to amphibians is urgent. Brandon Casey and Melissa Mohring, Wild Animal Keepers specializing in amphibians and reptiles at the Bronx Zoo, are very concerned. Casey notes that this is the "greatest mass extinction since the dinosaurs, but most people have no idea what’s going on." Unfortunately, says Mohring, amphibians "are overlooked. People hear them in the background and don’t really notice them."
Disturbingly, something about our world today puts more pressure on amphibians than ever before; as Kevin Zippel, Program Director of the Amphibian Ark, writes in an online article, "Amphibians persisted as the dinosaurs came and went, but today as many as half of all species are threatened with extinction." More than other types of animals, amphibians are in trouble. "For every threatened species of bird or mammal, there are two to three species of amphibian threatened with extinction," says Zippel.
According to the Bronx Zoo’s Curator of Herpetology, Dr. Jennifer Pramuk, "The greatest threat by far is habitat destruction. The second is emergent disease such as chytrid fungus and rana viruses. The third is probably habitat contamination. All of these threats are human induced."
Factors also include pollution, pesticides and an illegal pet trade. Experts disagree about whether or not climate change increases the spread of infectious diseases, thereby indirectly furthering the extinction. Nevertheless, no one disputes the fact that humans cause many of the problems facing amphibians today. For example, nonnative species brought by the dam construction in Tanzania could have introduced the fungus (or the fungus could have traveled along shoes or clothing) and thereby killed off the wild Kihansi spray toads. In addition, "predatory insects were able to live there once the spray stopped, since it was dryer," says Mohring.
Amphibians, such as frogs, toads, newts, and salamanders, are typically ignored among endangered animals. They are, however, essential to the balance of many ecosystems, serving as "keystone species," according to Casey, whose disappearance can cause systems to collapse. Some have biomedical importance for humans, as well. Substances secreted by their skin can serve as analgesics and pain relievers, and researchers recently discovered a substance from several species that prevents HIV. Their struggles might also foreshadow future threats to humans and the planet; with their permeable skin and shell-less eggs, amphibians are especially sensitive to environmental imbalances or stressors.
The two-part series on amphibian rescue will continue next week with an interview with Dr. Jennifer Pramuk, Curator of Herpetology at the Bronx Zoo.