Invasive species

Cinema and science fiction novels often make an issue of extraterrestrial species finding Earth, moving in, and generally messing things up. Well, if you’d like to read about that kind of thing, you don’t need to read science fiction—it happens right here on our own planet.

Invasive species are animals that have been artificially introduced to their current environment. Sometimes they are brought somewhere intentionally, other times they hitch a ride on cargo ships or trucks.

Typically, an invasive animal will fill an ecological niche that no animal currently fills, and it will be allowed to flourish. Unfortunately, sometimes the animal flourishes a bit too much, resulting in devastating consequences for the ecosystem.

The classic Aussie example is the cane toad, an animal purposefully introduced to control the cane beetle population. While the cane beetle problem lessened, the toads grew out of control. With no predators that can control its numbers, the cane toad ran rampant. It will eat any animal it can fit in its mouth, and is a carrier for diseases such as salmonella.

Another, lesser-known instance of invasive species is on Macquarie Island, just 1500 km southeast of Tasmania. The World Heritage-listed-island has historically been a natural refuge and breeding ground for many varieties of rare birds, including king penguins and two species of nationally threatened albatross.

Yet this site is becoming increasingly threatened by rabbits and other rodents. Since the 1980s, the rabbit population has increased from 10,000 to more than 100,000, all within an area of 128km2. All those rabbits need something to eat, and eat they do—so much, in fact, that they’ve totally stripped some hillsides of vegetation. This can be devastating during rainfall; during some months, as many as 20 landslides have occurred, sometimes killing penguins in the process.

There are several ways to deal with invasive species. The Tasmanian government has come up with a $15 million plan to completely eradicate the rodent population on Macquarie Island. After a similar program was successful on Campbell Island in 2001, conservationists are confident that this program would be effective on Macquarie Island as well.

The cane toad, however, is a bit more of a problem. It has become so widespread, stretching from Melbourne to Kakadu National Park, that the only effective removal takes place on the local level. Some people trap the toads, while others are doing research on a virus that would affect only the cane toad and destroy its population.

How do I know this?

Department of the Environment and Heritage 2004, The feral cane toad (Bufo marinus), http://www.deh.gov.au/biodiversity/invasive/publications/cane-toad/index.html

Wikipedia Free Encyclopaedia, Invasive Species, http://en.wikipedia.org/wiki/Invasive_species

WWF Australia 2006, Grey-headed albatross face extinction on Macquarie Island,http://wwf.org.au/news/grey-headed-albatross-face-extinction-on-macquarie-island

WWF Australia 2006, Precious island 'arks' under attack, http://wwf.org.au/articles/precious-island-arks-under-attack/

WWF Australia 2006, World Heritage island under threat, http://wwf.org.au/news/world-heritage-island-threatened-by-rabbits-and-rats/