Geoscience Reference
In-Depth Information
Cuba, and Colombia. Alligators and caimans are more common; but because of
human pressures, their populations have decreased significantly. Caimans can be
found from southern Mexico through northern Argentina. Most caiman species
grow to lengths of about 8 ft (2.5 m). The black caiman can reach lengths of nearly
20 ft (6 m). The black caiman, along with several other caiman and Neotropical
crocodiles, are endangered.
Amphibians of the Neotropics belong to three orders: salamanders and newts,
caecilians, and the largest group, frogs and toads. All amphibians require water to
reproduce and typically lay eggs in a gelatinous sac in ponds or streams, but in the
tropical rainforest, some lay eggs in bromeliads high in the canopy. Adults have
semipermeable skin and usually need to reside in moist environments; toads are
the exception.
Frogs are the most abundant and diverse amphibians in the Neotropical rain-
forest. Of the approximately 4,300 species of frogs and toads identified worldwide,
1,600 occur in the Neotropical rainforest. Frogs occupy a variety of niches and
have evolved strikingly different reproductive strategies. These include live births
of fully formed frogs, eggs laid on plants where the tadpoles can hatch and fall into
the water, eggs laid in foam nests in bromeliads and in tree cavities, and even eggs
that upon fertilization are moved to the mother's back, where the growing tadpoles
remain until they develop into fully formed frogs.
Pipid frogs are common and have flattened bodies and are tongueless. All are
aquatic with webbed feet. Frogs in the genus
Pipa
live in eastern Panama and South
America east of the Andes. The Surinam toad is about 7 in (178 mm) long with a
pointed head. It has a peculiar reproductive adaptation in that the male fertilizes
the eggs and distributes them over the female's back, where they become embedded
into small pockets and develop, emerging as tiny frogs.
The Neotropical frogs inhabit trees and shrubs, as well as leaf litter on the forest
floor. Most have direct developing eggs; that is, the tadpole stage is skipped and a
fully formed frog emerges from the egg. Many leptodactylid frogs lay their eggs in
foam nests that float on open water or deposit them in a tree cavity, burrow, or
other sheltered site. The foam provides a protective coating for the eggs and
tadpoles.
Toads are also common.
Bufo
species tend to be short legged and have heavy
bodies, wart-like glands on the body and legs, and a round or oval parotoid gland
behind the eye. They are toothless and tend to hunt at night.
Atelopus
is a genus
occurring in Central and South America made up of diurnal toads that are brightly
colored and produce a toxin. The coloration is thought to serve as a warning mech-
anism for potential predators.
Tree frogs are typically arboreal and possess well-developed finger and toe pads
to aid in climbing. Their eyes are positioned to provide binocular vision ahead and
at the periphery. Tree frogs of the genus
Phyllomedusa
have the first finger oppos-
able to the other three, allowing them to grasp twigs and stems. Some tree frogs lay
their eggs on plants above water so that the tadpoles can drop into the water when