Jumping marvels of the Amazon
Amphibians such as frogs usually keep close to bodies of water, where their skin can stay moist. In tropical rainforests however, the prevalent humidity enables them to occupy a much wider range. Not surprisingly, frogs are mostly found in trees, relatively safe from predators. This is where they also lay their eggs (on the underside of leaves or in water crevices), although some also lay them in the ground.
Poison dart frogs (Dendrobates species)Wildly coloured and notoriously toxic, poison dart frogs range from the rainforests of Central America to those of the Amazon Basin. Most of them live on the rainforest floor, although some prefer the safety of trees. They are most active in the daylight hours.
Poison dart frogs are small (20 mm-40 mm) photogenic animals that exhibit bright colours – bright red, orange or bright green - so that their predators can easily recognize them and stay safely away.
Still, some unwary small animals that come too close can be paralyzed by the poison excreted from the frogs’ skin. It is estimated that about 2.5 grams of the poison dart frog's poison could easily kill an adult human.
Some female poison dart frogs 'store' their tadpoles in tree crevices or the water-filled axils of bromeliads. The mother will make many return trips to each tadpole, depositing unfertilized eggs for them to eat.3
The poison dart frog gets its name from a group of Amazon indigenous people who cover the tip of their darts with the frog poison to kill their prey.
Giant cane toad (Bufo marinus)4
The giant cane toad is a large frog species. Its skin secretes an irritating fluid, so potent that dogs and cats die just from picking up the frog in their mouth. But even coming too close can be dangerous. From its back, the giant cane toad can discharge white venom, which contains bufotoxin.
The effects of contact with bufotoxin are varied and unpleasant: copious salivation; twitching; vomiting and collapse of the hind limbs. Bufotoxin can cause temporary paralysis or even death of small predators.
A particularity of male giant cane toads is the ability to reproduce as either male or female. They possess a rudimentary ovary that becomes operative if their testes are removed or damaged.
The giant cane toad has become a notorious pest. Its efficient venomous weaponry gives it a clear advantage over native amphibians and also causes predator declines, since these predators have no natural immunity to the bufotoxin it secretes. It has been called one of the100 most invasive species worldwide by the Invasive Species Specialist Group5.
1Da Silva et al. 2005. The Fate of the Amazonian Areas of Endemism. Conservation Biology 19 (3), 689-694
2Rodriguez, 1995 in Kricher, 1997
3Heying, H. 2003. "Dendrobatidae" (On-line), Animal Diversity Web. Accessed October 11, 2005 at http://animaldiversity.ummz.umich.edu/site/accounts/information/
4Hilgris, R. 2001. "Bufo marinus" (On-line), Animal Diversity Web. Accessed October 06, 2005 at http://animaldiversity.ummz.umich.edu/site/accounts/information/
5Invasive Species Specialist Group, 2005. "Bufo marinus" (On-line). Global Invasive Species Database. Accessed July 28, 2005 at http://www.issg.org/database/species/ecology.asp?si=113&fr=1&sts=.