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Posts Tagged ‘amphibian’

Cane toad (by Sam Fraser-Smith)The cane toad Bufo marinus is originally from South and Central America. In 1935, 101 adult cane toads (followed by a further 62,000 juveniles by 1937) were released in Australia to act as a natural control (through predation) of destructive sugarcane beetles. As often seems to occur however, this biological control itself got out of control – the cane toad rapidly expanded its range and population, and has seriously affected native Australian species.

Cane toads can produce up to 35,000 eggs per female several times each year. The tadpoles quickly develop in just 15-70 days and within a year the toads are adults and ready to breed. Toad appetites are wide-ranging so, unfortunately, the cane toads don’t stick to their proposed diet of sugarcane beetles, but also eat other invertebrates and small vertebrates, such as native Australian frogs, putting pressure on these populations. The cane toad is poisonous in all of its life stages (i.e. as egg, tadpole and toad) and while in the Americas predators such as caiman, snakes and birds have evolved to be able to safely eat the cane toad, this poison has meant that few Australian predators can do so and live to tell the tale; this low death rate results in the toad population continually increasing. The cane toad’s predator poisoning has been shown to detrimentally affect Australian predator populations, for example three lizard species’ populations declined by 80-90% once the cane toad moved in. Additionally, the decline of these lizards resulted in increased populations of their insect prey, as the latter came under less pressure from the predators.Cane toad (by Sam Fraser-Smith)

The cane toad, therefore, is listed by the IUCN’s Invasive Species Group as one of the world’s 100 worst invaders . Despite much research into species-specific diseases or biological control methods that could be used to reduce their numbers, no successful method has yet been found, so the search continues for a means to limit or eradicate the cane toad without affecting native Australian frog species.

References

Shanmuganathan T et al. 2010. Biological control of the cane toad in Australia: a review. Animal Conservation 13 Suppl 1: 16-23

Further Information

Australian Museum
Save the frogs
Cane toads in Oz
IUCN global invasive species database

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Common toad, Bufo bufoA paper in this month’s Journal of Zoology (1) suggests that the common toad, Bufo bufo, can possibly do just that. The ability to sense a coming earthquake has been suggested for many animals, but scientific proof is thin on the ground. A team monitoring toad mating behaviour in Italy in 2009, however, happened to record their data before, during and after an earthquake struck 74km from the study site. During previous years, once the toads started mating they would continue until the spawning season had finished, but in the year of the earthquake 96% of male toads disappeared from the site five days before the earthquake struck (the sample size of females was too small to analyse), and male toad numbers remained lower than usual until two days after the last aftershock. Fresh spawn (toad eggs) was seen six days before the main earthquake, and six days after it, but none was seen during the intervening earthquake period.

Toad behaviour is correlated closely to weather, but this male site-desertion did not correlate to maximum or minimum temperature, percentage humidity, wind speed, or rainfall – it did, however, correlate to the number of days before or after the earthquake (and the earthquake period), and the number of mating toad-pairs similarly correlated with days before or after the earthquake and earthquake period.

Common toad, Bufo bufo, mating pair (by HotShot²)How the toads predicted the earthquake is unclear but the authors suggest that they perhaps responded to a change in the Earth’s magnetic field (toads have been shown to react to geomagnetic fields in previous research), or to a rise in radon gas in the groundwater (which can occur before a big earthquake – again, toads are sensitive to changes in water chemistry), or to some other unidentified change to the ionosphere (one of Earth’s atmosphere layers). However they do it, it certainly seems that these toads could detect some sort of change in the ionosphere that allowed them to predict the earthquake was coming and move to safety before the earthquake struck, which is pretty amazing.

 

References

  1. Grant RA & Halliday T 2010 ‘Predicting the unpredictable; evidence of pre-seismic anticipatory behaviour in the common toad’. Journal of Zoology 281: 263-271

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