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Members of this family
are found worldwide, but they have a limited distribution in South
America and Australia. They do not occur in the West Indies, nor
on most oceanic islands. In many parts of the world the frog population
has declined drastically over the last few decades. Pollutants
are one cause for this decline, but other culprits include climatic
changes, parasitic infestation, introduction of non-indigenous
predators/competitors, infectious diseases, and urban encroachment.
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The life cycle
of a frog involves several stages. Typically adult frogs gather
in suitable pools, the first to arive usually being the males.
Their croaking may well encourage the females to arrive. A female
would wish to avoid arriving at a pond which did not have any
males in attendance. Gravid female frogs are actively and persistently
sought out by males and many males will often try to attach themselves
to a single female but eventually one male will secure possession.
Amplexus is the process wherein the male grasps the female while
she lays her eggs. At the same time, he fertilizes them with a
fluid containing sperm. The eggs are about 2.0 to 2.8 millimetres
in diameter and are dark brown and are covered in an outer shell
of gelatinous transparent material which swells in contact with
water. The female frog lays her eggs in a shallow pond or creek,
where they will be sheltered from the current and from predators.
The eggs, known as frogspawn hatch into tadpoles. The tadpole
stage develops gradually into a froglet, resembling an adult but
retaining a vestigial tail. Finally the froglet develops into
an adult frog. Typically, tadpoles are herbivores, feeding mostly
on algae, whereas juvenile and adult frogs are rather voracious
carnivores.
001-013.jpg courtesy Us Fish and Wildlife Service
014-016.jpg courtesy: National Undersea Research Program
017-018.jpg courtesy: pdphoto.org
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