'Disappearing' Frogs
Frogs are known to indicators of ecosystem health (or bio-indicators), because as skin-breathers they are affected by environmental poisons such as pesticides and herbicides. Evidence from captive breeding and keeping, field monitoring and tissue testing of frogs has identified some other causes for frog decline.
In 1993, two leading frog researchers Glen Ingram of the Queensland Museum and Keith McDonald documented the decline of some species of frogs from upland Queensland rainforests. Seven species of frogs had disappeared and another four had seriously declined since 1979. One species, the Southern Platypus Frog or 'gastric brooding frog', was considered unique because its tadpoles developed in the mother's stomach.
Similar declines in frogs have been reported in North and South America, Europe, and South Africa; areas with active biological research communities. In south-east Asia and New Guinea where there has been no monitoring, no one can say if their frog populations are secure.
Chytrid (kit-rid) fungus
Chytrid fungus has probably contributed to the mass deaths observed by researchers. This fungus feeds on keratin, a tough protein found in the skin on the hands and feet of adult frogs and in tadpole mouthparts. Frogs affected by chytrid fungus develop thickened and peeling skin, become lethargic and lose hind leg movement. They die a few days to weeks after these symptoms first appear for reasons not yet known. Infected tadpoles die shortly after metamorphosis. So far, scientists have found affected frogs are mainly large-bodied and live in mountain streams, but much more research needs to be done on this disease.
Habitat destruction and degradation
Human habitation of coastal areas of Queensland has altered or destroyed many frog habitats. Changes include the clearing of wetlands for real estate, the damming of rivers, cattle damage and introduced fish, which are predators of tadpoles. For example, Mosquitofish or Gambusia caused the extinctions of bell frogs in south-east Australia.
Climate change
Scientists predict global warming will cause unprecedented worldwide changes to rainfall and temperature. Rapid climate change will be catastrophic for frogs, because they need water for tadpole development, and this makes migration difficult.
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