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Monkey frog (Phyllomedusa bicolor) in the rainforest of Peru. (Photo by R. Butler)
Frogs are overwhelmingly the most abundant amphibians 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.
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.
Insects are the most successful rainforest animals as demonstrated by their tremendous diversity. Insects are so ubiquitous that they have filled many niches usually occupied by other animals. For example, some postulate that in South America the role of the forest elephant is filled by army ants. In the rainforest canopy, insects abound: a study of the rainforest canopy in Peru with 500 cubic meters of foliage (about the size of a two-car garage) found more than 50 species of ants, 1,000 beetle species, 1,700 arthropod species, and more than 100,000 individuals. A rainforest tree alone can have some 1,200 species of beetle, while a single hectare of rich forest canopy is projected to have 12,448 beetle species.
There are many insects and other invertebrates that would not usually be considered arboreal but exist in the rainforest canopy. For example, several species of crabs have been found hundreds of feet above the ground in tank bromeliads of neotropical forests. Similarly, earthworms and giant planarians (flatworms) are also part of the canopy system, with earthworms playing an important role in the processing of canopy soils and mulch that supports epiphytic growth. Even leeches are found in the canopy where they may surprise first-time visitors to the Asian forest canopy. Mosquitoes, too, are abundant in the canopy, though on the ground there are generally few puddles for breeding and no pronounced seasonal changes to stimulate massive mosquito-breeding frenzy. In the canopy, mosquitoes lay their eggs in the up-turned leaves of epiphytes like tank bromeliads. Therefore, you may be more likely to get mosquito bites in the canopy than on the forest floor.
Many insects like stick insects, katydids, leaf hoppers, and mantids have developed incredible behavior, body structure, and color to mimic their surroundings. These insects, which mimic dead and living leaves, half-eaten leaves, sticks, bark, bird droppings, and flower parts, avoid detection by predators and prey as they hunt and rest.
Photos of newly discovered species in Brazil's Cerrado
(4/29/2008) An expedition to Brazil's Cerrado has turned up more than a dozen undiscovered species. Conservationists say the discoveries add urgency to protecting the grassland habitat which is rapidly being converted for agriculture.
Lungless frog discovered in Borneo
(4/11/2008) A lungless frog has been discovered on the island of Borneo. Scientists say the species may shed light on the process of evolution in some organisms.
New map sets conservation priorities for Madagascar
(4/10/2008) Compiling data on thousands of endemic species of ants, butterflies, frogs,
geckos, lemurs and plants, an international team of researchers has developed a comprehensive biodiversity map of Madagascar that will help determine determine future reserve placement and conservation planning on the Indian Ocean island and beyond.
No global warming link to dying frogs?
(3/25/2008) Scientists have fired another salvo in the heated debate over the role of climate change in the global decline of amphibians. Writing in the March 25 issue of PLoS Biology, a team of researchers led by Karen Lips of Southern Illinois University-Carbondale report finding "no evidence to support the hypothesis that climate change has been driving outbreaks of amphibian chytridiomycosis" -- a disease blamed for large-scale die-offs of amphibians. Other researchers have argued that climate shifts are worsening the outbreak of the fungal disease.
How falling a gecko lands on its feet
(3/17/2008) According to new research the gecko may have the most dynamic tail in the natural world. Two researchers from UC Berkley have discovered that the gecko uses its tail to keep itself from falling off slippery vertical surfaces and when falling to rapidly right itself. So, like a cat, it always lands on four feet.
