 Numerous potential explanations for amphibian declines have been proposed . Most or all of these causes have been associated with some population declines , so each cause is likely to affect in certain circumstances but not others . Many of the causes of amphibian declines are well @-@ understood , and appear to affect other groups of organisms as well as amphibians . These causes include habitat modification and fragmentation , introduced predators or competitors , introduced species , pollution , pesticide use , or over @-@ harvesting . However , many amphibian declines or extinctions have occurred in pristine habitats where the above effects are not likely to occur . The causes of these declines are complex , but many can be attributed to emerging diseases , climate change , increased ultraviolet @-@ B radiation , or long @-@ distance transmission of chemical contaminants by wind . 
