Cane Toads, ranked as the most invasive species in Australia, have toxic glands that secrete deadly poisons. Invasive species means that the species is not native to the area, and was introduced by humans. In this particular case, the cane toads were brought to Australia in the 1935, in an unsuccessful attempt to control insects that ate and killed commercial sugar cane crops. Since they were introduced to their new habitat, this toad species has thrived, but they have had harsh effects on the native wildlife of Australia. These toads have killed many marsupials on the way to getting rid of pests that were eating the crops, and all efforts to slow down the rate of toad invasion seem to have failed.
Some native species have done very well while the toads are around; however, the native northern quoll has not been so lucky. The northern quoll has taken to feasting on the abundant cane toads; therefore, their numbers have fallen very low, and they have even gone extinct in certain parts of Australia. One of the main reasons for this extinction is the presence of the cane toads. One possible way to keep the northern quolls from using this poisonous toad species as a source of food would be to use conditioned taste aversion. Conditioned taste aversion happens when an animal has had a bad experience with certain food sources and then stays away from eating or attacking that particular type again. A study was done to see if the northern quoll would in fact learn to stay away from the toads. To do so, dead toads infected with a special chemical to make the quolls nauseous were fed to a number of young quolls. The study proved that the quolls who had a bad experience with the toads were able to survive much better than the ones that did not eat the dead toads. It is believed that this could be a possible solution for any type of animal that uses cane toads as a food source.
Another study, investigated whether or not the flattened, dried out bodies of dead cane toads could still pose a threat to the native aquatic species. They tested this by placing tadpoles of a native species of toad and tadpoles of the toxic cane toad, as well leeches and fish into water. The tadpoles were placed in water with direct access to the dead tissue. The native tadpoles were affected by the presence of the dead carcass, but the cane toad tadpoles were not. In a different area the leeches, fish and native tadpole were placed in water where there was a carcass separated by a screen mesh (indirect access). In this case mortality rates were higher among the tested species, showing that the dead toad bodies did affect the animals by simply being present in the water.
How could these effects be reduced so that the native populations could continue to thrive? Controlling the population size would help to lower the negative effects on the native wildlife and their habitats. One study explored the possibility of using a native predator to control their populations. The predator in mind is the meat ant which will kill and eat cane toads. The toads spawn in lakes near vast areas of dry ground perfect for ant nests. When the meat ants are present in larger numbers, fewer toads are present because the rate of interaction is much higher. Both the meat ants and toads are diurnal, which means they are both active during the day; therefore, the predator-prey system would work perfectly. The study showed that using the meat ants is an effective way to control the cane toad population.
How could these effects be reduced so that the native populations could continue to thrive? Controlling the population size would help to lower the negative effects on the native wildlife and their habitats. One study explored the possibility of using a native predator to control their populations. The predator in mind is the meat ant which will kill and eat cane toads. The toads spawn in lakes near vast areas of dry ground perfect for ant nests. When the meat ants are present in larger numbers, fewer toads are present because the rate of interaction is much higher. Both the meat ants and toads are diurnal, which means they are both active during the day; therefore, the predator-prey system would work perfectly. The study showed that using the meat ants is an effective way to control the cane toad population.
As seen, the cane toads have a huge effect on the native wildlife such as northern quolls, as well as negative effects on the aquatic wildlife. However, two different solutions were presented to reduce the effects. The first uses meat ants as a main toad predator to reduce the overall number of toads. The second, involves feeding young quolls (or other animals preying upon the deadly toads) dead toads with nauseating chemicals so that they learn from their bad experience and stay away from using the toads as a food source. Hopefully, these methods can undo the damage caused by introducing this toxic species.
Sources:
- Crossland, M., Brown, G., Shine, R., 2011. The enduring toxicity of road-killed cane toads (Rhinella marina). Biological Invasions 13:2135-2145
- Mahoney, J.A.; Ride, W.D.L. (1984). "The Identity of Captain Cook's Quoll mustella quoll Zimmermann 1783 (Marsupialia: Dasyuridae)". Australian Mammalogy 7: 57-62.
- O’Donnell, S., Webb, J.K., Shine, R., 2010. Conditioned taste aversion enhances the survival of an endangered predator imperilled by a toxic invader. Journal of Applied Ecology 47: 558-565
- Ward-Fear, G., Brown, G.P., Shine, R., 2010. Using a native predator (the meat ant, Iridomyrmex reburrus) to reduce the abundance of an invasive species (the cane toad, Bufo marinus) in tropical Australia. Journal of Applied Ecology 47: 273-280.
