Why are polar bears and amphibian populations declining? Is it due to global warming, deforestation (for the amphibians), or something else?
The major cause of the decrease in the polar bear population is climate change, due to which polar ice is melting. Polar bears make a living on the arctic ice; as it melts their habitat is destroyed. The ice platforms are also moving farther apart which makes swimming conditions difficult. Other factors destroying their habitat and reducing their numbers include hunting, oil exploration and toxic pollution.
Amphibians are among the most threatened vertebrates. It has been estimated that almost 40% of the amphibians are threatened with extinction, as compared to 12% birds and 25% mammals. One of the principle causes of the amphibian population's decline is the rapid spread of a disease known as Chytridiomycosis, for which we do not yet have a cure. Another factor is the loss/alteration of habitats due to anthropogenic activities, chiefly deforestation and pollution.
Hope this helps.