Frogs are overwhelmingly the most abundant amphibians (pictures | news) in the rainforest. Unlike temperate frogs that are mostly limited to habitats near water, tropical frogs are most abundant in the trees, and relatively few are found near bodies of water on the forest floor. The reason for this is quite simple: frogs must always keep their skin moist since almost half of their respiration in carried out through the skin. The high humidity of the rainforest and frequent rainstorms gives tropical frogs infinitely more freedom to move into the trees and escape the many predators of rainforest waters.
The differences between temperate and tropical frogs extend beyond their habitat. Whereas nearly all temperate frogs lay their eggs in water, the majority of rainforest species place eggs in vegetation or lay them in the ground. By leaving the water, frogs avoid egg-predators like fish, shrimp, aquatic insects, and insect larvae. Several species of frogs, including the American glass frogs, lay their eggs on vegetation that overhangs water. The humid climate keeps the eggs moist and when the tadpoles hatch they drop into the water below. Glass frogs are also interesting because they are transparent except for their visible organs and the faint yellow spots that some species possess. These yellow spots resemble a cluster of the frog's eggs, enough to fool predators. Other frog species develop fully into froglets within their eggs, and emerge as fully formed frogs, thus by-passing the tadpole stage altogether.
REPTILES
When many people think of the "jungle," they think of huge deadly snakes; but this is not the case in the canopy where very few species pose any threat to humans. The majority of canopy snakes are constrictors or mildly venomous species and are rarely encountered by humans. Even in the canopy, chances are you will not see many snakes, since numerous species camouflage themselves like leaves and vines.
The best known venomous canopy-dwelling snake is the eyelash viper of the New World which exists in several different color forms including yellow, green, olive, and orange. The eyelash viper is so named for the presence of small horned scales above the eye. Also found in the canopy are various constrictors of the Boa family which use their strong muscles to constrict their prey to death.
In addition to snakes, the forest canopy contains lizards. Iguanas are large greenish lizards of the New World, which have the unique ability to drop over 60 feet (18 m) from canopy trees unharmed. Their strong tail is used for balance during the fall and catching branches during the descent to break the impact of the fall. Iguanas often inhabit limbs that overhang rivers so they are able to escape predators by dropping into the river and waiting submerged for over 30 minutes. Iguanas may attain a length of six feet (1.8 m), though they are generally smaller. Iguanas have the ability to undergo a small color change to better blend into their surrounding environment. But the true color-change artists of the forest are the chameleons—of which every forested continent has its own. Chameleons are lizards that have the ability to rapidly change their colors to match their surroundings, although they tend to change more in accordance with their emotions. The Old World or true chameleons of Africa and Madagascar (pictures) have the best color-change ability and will often assume bright orange, purple, and blue coloring to reflect their mood. South America has the anole, a much less spectacular chameleon, while Asia has the agamas.
Monkey frog (Phyllomedusa bicolor) in the rainforest of Peru. Click image for more photos of herps. (Photo by R. Butler)
Review questions:
What is the most abundant type of amphibian in the rainforest?