Populations of several frog species found in mountain habitats have declined dramatically. These high-elevation species bask in the sun and are dark in color, adaptations to help keep the animals warm in cold conditions. These same tendencies may cause greater absorption of harmful radiation. Introduced Species Researchers in Yosemite National Park surmise that introduced trout and bullfrogs have contributed to the decline of native amphibians. When the Park was first formed, sport-fishing enthusiasts stocked trout in many lakes which had no natural fish populations.
Trout are both a predator of and competitor with the native frogs.
The fish eat amphibian eggs and larvae and also eat the same insect prey as adult frogs. The bullfrog, which has thrived and spread, is known to eat and out-compete native frogs. Disease For amphibian populations already stressed by pollution, habitat loss, or other factors, the introduction of a new disease can be deadly. Scientists suggest that the mass disappearance of frogs seen in the Australian rain forest may be due to an epidemic of an exotic disease. The increasing trade in plants and animals for aquariums may be transporting between continents diseases to which amphibians are particularly susceptible.