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 Vanishing SpeciesWhat is Threatening Species? Pollution and Disease Pollution by acid rain and acid from coal mines that drains into streams and rivers, heavy metals, PCBs, dioxin and other toxic chemicals, have killed off all life in waterways in many parts of the world. PCBs and pesticides have caused serious genetic malformations in frogs, birds and fish.
Frogs have been dying from fungal diseases and the indirect effect of other pollutants, which are eliminating entire species. Necropsies done on frogs from Australia and Panama, which were found dying, have revealed the presence of the same fungus, chytrid (Morell 2001). It is considered responsible for the extinction of several Australian frogs, including the extraordinary Gastric-brooding Frog (Rheobatrachus silus) and three other species, and has infected frogs in Panama as well, eliminating populations and possibly species (Morell 2001). This fungus has been detected in 44 species of Australian frogs and is apparently spreading in many parts of the world. Other fungi and viruses have eliminated frogs in the United States (Morell 2001). These diseases have long been in the environment, and it is not yet clear why they have become so toxic and virulent to frogs. Frogs have thin skin and easily absorb chemicals, making them vulnerable, but apparently their immune systems have been weakened, as well. Frogs and toads are also threatened by pesticides, which have been shown to cause grotesque deformities and mortality. Many types of pollution, including acid rain, heavy metals and fertilizers, have eliminated frogs in many parts of Europe and Canada (Morell 2001). Ultraviolet radiation (UV) suppresses frogs' immune systems and kills eggs as well as adults. Andrew Blaustein (1994), an American biologist, conducted experiments that proved UV to be responsible for wiping out many species of frogs in the US West who laid their eggs in the open. The eggs were thus exposed to this radiation, which has intensified as a result of the decrease in the ozone layer caused by chloroflourocarbons, used by industry in air conditioners and refrigerators, among other industrial uses (see Aquatic Ecosystems chapter).
Hawaiian birds have been seriously affected by avian malaria, brought to the islands by captive cage birds, as discussed in Chapter 1. This disease continues to threaten the surviving species of native birds, and is a major cause of the wave of extinctions that is claiming one species after another of these beautiful songbirds (BI 2000). Several species, such as the Nukupu'u (Hemignathus lucidus), are now in Critical status, possibly extinct on both Kauai and Maui where, until the 1990s, a few birds were seen in their montane forests (BI 2000). Feral pigs in their habitats facilitate the spread of alien plants and introduced, disease-carrying mosquitoes (BI 2000).
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