Amphibian Invaders: Down Under and All
Around
by Howard Youth
Not all amphibians are suffering declines. Some, in fact, are flourishing in places they don't belongand causing serious ecological problems. Consider the giant toad (Bufo marinus), originally a native of French Guiana in South America. Now probably the world's most widely introduced amphibian, this cow-pie-sized eating machine was carried to various sugar-growing countriesincluding many Caribbean islands, Australia, Taiwan, Japan, the Philippines, and the Micronesian islandsto dine on crop-eating beetles. Ugly and loud (choruses remind some of idling diesel engines), giant toadsor cane, or marine toads as they are also knowngobble down almost anything that strays before them, including native wildlife.
Giant toads also are highly toxic. Predators often die after biting into the bulging, poisonous parotid glands that sit behind the toads' eyes. Once toad-less, Australia now seethes with the warty invaders, which arrived in 1935. Still on the march, giant toads continue to spread across the warm north of Australia, heading into the Outbacks vast, primeval marshlands. Millions of dollars have been spent to stem the tide since the toads began their rampage, and Australian scientists are scrambling to isolate a pathogen that could weaken or kill off the hungry toad horde, while not affecting their countrys sensitive native frogs.
Other recent amphibian invasions include tiny Puerto Rican coqui frogs (Eleutherodactylus coqui) now thriving in Hawaiiwhere their loud, beeping choruses disturb hotel-bound touristsas well as treefrogs from mainland Ecuador that have popped up in settled areas of the Galapagos Islands. (Neither island chain has native amphibians.) The lake frog (Rana ridibunda) has been introduced to wetlands in Russia's Ural Mountains, where it displaces native species, while Cuban treefrogs (Osteopilus septentrionalis) brought to south Florida are eating the indigenous treefrogs there.
Meanwhile, an all-American favorite, the bullfrog (Rana catesbeiana), is bullying its way across the U.S. West (where it's not native), as well as Europe, parts of South America, Israel, Indonesia, Malaysia, and Singapore. With its large, luscious legs, the bullfrog has most often been introduced as a food crop. Like the giant toad and other invaders, it out-competesor consumesnative amphibians and other small animals in its conquered territory.
"Bullfrogs will eat anything that moves that they can fit into their mouthseven each other," says Mike Lannoo, an associate professor at Indiana University School of Medicine, and member of DAPTF's Invasive Species Specialist Group. Generally speaking, says Lannoo of the bullish invaders, "where bullfrogs are, other amphibians aren't."
-Howard Youth
ZooGoer 29(2) 2000. Copyright 2000 Friends of the National Zoo. All rights reserved.
