South America is home to a diverse assortment of frogs and toads, many of which secrete poisons as a means of defense. The continent owes its frog and toad diversity largely to the presence of the biologically rich Amazon rain forest. South America's amphibian populations have nonetheless decreased considerably in part because of the spread of a deadly fungus.
Small but Deadly
Though they measure a couple of inches at most, the more than 100 species of brilliantly colored poison arrow frogs found in the tropical forests of Central America and South America are among the most toxic organisms in the world. Insectivorous and diurnal, poison arrow frogs come in blue, yellow, red and other colors. They have only one natural predator, a snake known scientifically as Leimadophis epinephelus that is unaffected by the potent venom found in the skin of the snake's poison arrow prey.
On the floor of South America's tropical forests, horned frogs of the genus Ceratophys hide beneath leaf litter and wait in ambush for unsuspecting prey -- insects, lizards, mice or any animals smaller than themselves -- to approach. The insatiable appetite of these amphibians, which include the Amazon horned frog and the ornate horned frog, is consistent with their size; horned frogs can measure half a foot and weigh about a pound. Their "horns" are actually folds of skin above their eyes.
Life in the Trees
Equipped with toe pads that enable their largely arboreal lifestyle, frogs of the family Hylidae, considered true tree frogs, have worldwide distribution. In South America, representatives include the giant leaf frog and the waxy monkey frog. Both species get around by climbing rather than hopping; both have waxy coatings on their skin that help them retain moisture when they are exposed to the sun. Also classified in the Hylidae family are the Amazon milk frog, which gets his name from his white toxic secretions, and the continent's marsupial frogs, whose eggs hatch inside pouches on mothers' backs.
Toads in Trouble
Among the most imperiled amphibians in South America are the harlequin, or stubfoot, toads of genus Atelopus. In contrast with most other toads, they come in a variety of vivid colors. Their bright hues indicate toxicity. Some of the species considered critically endangered, like the Rio Pescado stubfoot toad of Ecuador and the scarlet harlequin toad of Venezuela, have extremely restricted ranges. South America's toad diversity includes species of genus Bufo, such as the smooth-sided toad and the cane toad, both of which live in the Amazon rain forest and are poisonous.
The global outbreak of a chytrid fungus called Batrachochytrium dendrobatidis, which causes a deadly skin disease in amphibians known as chytridiomycosis, is largely to blame for the decline of South America's harlequin toads. The fungus is considered responsible for the extinction of around 70 harlequin toad species, as well as the Darwin frog, a South American species in which males used their vocal sacs to transport tadpoles.
- New Hampshire Public Television: Anura - Frogs, Toads
- Smithsonian National Zoological Park: Poison Dart Frog Fact Sheet
- World Association of Zoos and Aquariums: Frogs and Toads
- Rainforest Alliance: Poison Dart Frog
- Smithsonian National Zoological Park: Ornate Horned Frog
- National Aquarium: Giant Leaf Frog
- National Geographic: News Watch - St. Louis Zoo to the Harlequin Toad Rescue
- Conservation International: Rio Pescado Stubfoot Toad
- IUCN Red List of Threatened Species: Atelopus Sorianoi
- University of Michigan Animal Diversity Web: Hylidae
- Audubon Nature Institute: Amazon Milk Frog
- Encyclopedia Britannica: Tree Frog
- Amphibian Ark: Chytrid Fungus
- Encyclopedia Britannica: Amazon Rainforest
- National Geographic: News Watch - Why Has the Darwin’s Frog Likely Gone Extinct?
- Smithsonian National Zoological Park: Amphibian Conservation Program
- Jupiterimages/liquidlibrary/Getty Images