The Biology Behind The Toads

A Cane Toad or Rhinella Marina

Biological Profile: Cane Toad

Phylum: Chordata

Class: Amphibia

Order: Anura

Family: Bufonidae

Genus: Rhinella

Species: Rhinella Marina/Bufo Marinus

Length: 4-6 inches

Weight: 2.9 Pounds

Lifespan: 5-10 years

Diet: Omnivorous

Native Habitat: Americas

(National Geographic, 2014)

A Cane Toad Secreting Bufotoxin from its Parotoid Glands

The cane toad is a large, warty amphibian that finds its roots in the Americas.  It is one of the largest toads in the world, growing to sizes upwards of 6 inches and weighing nearly 3 pounds (National Geographic, 2014). This toad is an omnivore with a diverse diet consisting of anything from insects to small plants to rats. In addition to its size, the toad utilizes a type of venom called Bufotoxin to deter predators. This venom manifests in the form of a milky white fluid secreted from the parotoid glands, glands that are located just behind the ears of the toad. This venom is highly toxic, proving fatal to many forms of wildlife and is a major irritant to humans (and can be deadly if ingested). The cane toad earned its name when farmers in the Americas noticed that it was very effective at removing pests that plagued crops such as sugar cane. This utility led to the cane toad becoming widely introduced in several areas of the world, with most endeavors proving fruitful. 

A Cane Toad Consuming a Mouse

It was when the toad was introduced to Australia that disaster struck. Intended to control pest population among sugar cane farmers as they did in other areas like the Philippines and Hawaii, the cane toad was imported into eastern Australia in 1935 with the hope that they could increase crop yield (National Geographic, 2014). The farmers failed to realize that the pests, unlike in other areas, lived in the upper areas of the sugar cane. This put them well out of the reach of the toads (National Geographic, 2014). Fortunately for the toads and unfortunately for the farmers, the diverse diet of the cane toad allowed it to feast on other animals and plants. In an environment devoid of its natural predators, the cane toad thrived, its population exploded, rising from an initial number of roughly 3000 to a number well in the millions today (National Geographic, 2014). It quickly became one of the most infamous examples of an invasive species, boasting a combination of long lifespan, large size, quick reproductive rate, and lifelong toxicity. These assets have made the cane toad population very difficult to whittle down.

Cane Toad Distribution in 2008 w/ Potential Habitat

Their introduction into the Australian ecosystem has had catastrophic ecological consequences. As mentioned above, the toads are now classified as an invasive species in Australia, having spread from their initial introduction point in the east to parts of Western Australia. Females lay anywhere from 8,000 to 35,000 eggs, and while only a small percentage often survive, those that prey on the eggs often die from their poison (Cameron, 2013). The tadpoles that do hatch are, again, poisonous, and often prove fatal for would-be predators. This wreaks havoc on larger creatures, diminishing their populations and allowing their prey to reproduce. The toads then grow up to feed unimpeded, devouring insects and small animals. This, in turn, starves the native Australian insectivores. The toad’s diverse diet also impacts herbivores, as they can and will consume the plants around them. The cane toad also has had urban impacts as well, as their venom is fatal to most domestic animals such as dogs or cats. They have also been known to eat pet food out of the bowls left outside houses (Commonwealth of Australia, 2014). All of these factors add up to disruped food chains and broken relationships of symbiosis.

All of this damage ends up having diverse effects of Australia’s native food chains and population cycles. All have been disrupted by the invading cane toad (Government of Western Australia, 2005). In addition to the food chains, many symbiotic relationships have been disrupted or eradicated by the cane toad.  A few examples of animals affected by the cane toad are the quoll, certain types of snake, goannas (a type of monitor lizard) and even crocodiles. The impact of this ecological disruption is most evident in the case of the yellow-spotted monitor lizard, whose population has been estimated to have dropped by nearly 90% since the introduction of the toads(National Geographic, 2014). All in all, though the introduction of the cane toad was meant to benefit all parties involved, the import has actually done far more harm than good.









References:

"Australian Government policy on cane toads." Department of the Environment. Commonwealth of Australia, n.d. Web. 19 Feb. 2014. <http://www.environment.gov.au/node/139>.

Cameron, Elizabeth. "Cane Toad - Australian Museum." Cane Toad - Australian Museum. Australian Museum, 11 Sept. 2013. Web. 20 Feb. 2014. <http://australianmuseum.net.au/Cane-Toad>.

"Cane Toad." National Geographic. National Geographic, n.d. Web. 19 Feb. 2014. <http://animals.nationalgeographic.com/animals/amphibians/cane-toad/>.

"Department of Agriculture and Food Western Australia." Department of Agriculture and Food. Government of Western Australia, 12 Aug. 2005. Web. 20 Feb. 2014. <http://archive.agric.wa.gov.au/PC_91730.h>.