Amphibian decline: a case study in western Sydney
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Few quantitative data exist on the anecdotal observations of many researchers which apparently indicate a global decline of Amphibia in both disturbed and seemingly pristine habitats. This study was initiated to determine the responses of frogs to local, human-induced environmental stress. Frogs were collected from six sites near Richmond in western Sydney between June 1991 and February 1992. Two sites were undisturbed, having little disruption to their natural vegetation and catchment, while four were disturbed being subject to habitat destruction and water pollution from surrounding towns and rural areas. Site similarity coefficients as assessed by the Ochiai index indicated significant differences in diversity and abundance of frogs between disturbed and undisturbed areas. The disturbed sites were degraded, mainly through clearing of upper storey vegetation and this was probably the major effect in reducing both numbers and diversity in these sites. Other probable factors involved in the localized decline of frogs were residues of pesticides and heavy metals, parasite load and the level of predation. Frogs collected from the disturbed sites had significantly higher numbers of trauma-induced external abnormalities than did those from undisturbed sites. The incidence of non-traumatic abnormalities was low at all sites. Frog populations in western Sydney were good indicators of human-induced environmental change. In disturbed areas, frogs are under considerable pressure from rural and urban expansion. Further urbanization of this area will almost certainly have a profound impact on frog populations and conservation of wetland habitats is imperative if the decline in both abundance and diversity of frogs in this area is to be halted.