Frog
Amphibians include 2 major groups: the salamanders, which have tails and generally travel by walking or creeping; and the frogs and toads, which as adults are tailless and travel by hopping. With some notable exceptions, both groups pass their larval stage as gilled tadpoles in aquatic habitats of various sorts. Salamander larvae tend to be carnivorous while anuran larvae tend to be herbivorous; as adults, both groups feed primarily on insects and other small invertebrates.
Anurans emerge from their natal wetlands as they metamorphose to adult form, and spend most of their adult life on land. Some, such as the green frog, mink frog, and bullfrog, rarely leave water. Early breeders tend to lay their eggs in temporary ponds where predators such as fish cannot survive. These tadpoles must grow quickly so they can metamorphose before ponds dry up in late summer. Late breeders, like the Green Frog, lay their eggs in permanent water, and tadpoles may not metamorphose until the second year. At breeding sites, male frogs and toads make their presence known with distinctive calls.
Possible widespread declines in amphibian populations are disturbing because of the important roles of amphibians in many ecosystems. Their complex life cycles, insectivorous habits, permeable skin, and sensitivity to water chemistry in the egg and larval stages probably make them good bioindicators of environmental stress. There is little geographic or taxonomic pattern to the reported declines, some of which are from sites free of local anthropogenic disturbance. Causes for decline are usually unknown, and may be various, including habitat destruction, chemical contamination, introduction of predators, global climatic changes, acidic precipitation, or combinations of these factors.
September 25, 2006 3:08 PM | Category: Animals, Pictures