Tuesday, February 7, 2012

Elephants Down Under

Gamba grass is a tall grass native to Africa that is now an invasive pest species throughout northern Australia.  A biologist specializing in the relationship between plants, the environment, and global climate change from the University of Tasmania, Dr. David Bowman, has discussed his ideas to return ecosystems to a more native state by introducing large plant-eating animals native to Africa, including elephants, to Australia to control Gamba grass in a Comment in Nature published February 2, 2012.

Gamba grass is considered a pest species because it is not native to Australia and is damaging to the ecosystem it has invaded.  Fire is a natural component of the Australian environment with many plant species being fire dependent, meaning their life cycle relies on a semi-regular fire cycle.  The invasion of Gamba grass has increased the amount of fuel, meaning fires are now too frequent and too hot for native species of plants to survive.  It is this potential to do damage that makes Gamba grass a pest species, not just the fact that it is unwanted.  For example, rabbits are native to North America but are not native to Australia.  Therefore, in North America rabbits are merely an annoyance to gardeners, but in Australia rabbits are an invasive and non-native pest species.

When pest organisms invade an area, the usual methods of control involve chemicals with unhealthy side effects for the surrounding ecosystem or professional hunting expeditions that are inefficient and economically draining.  Using other organisms to control the pest, like the idea of using elephants to eat Gamba grass, may appear to be a natural alternative, but introducing another non-native species to control one pest will likely add environmental stressors to the ecosystem.  Just as in Shakespeare, there are no small roles in an ecosystem; non-native species impact their host ecosystem often through unforeseen consequences.  This act has been performed in Australia before with no call for an encore.

When sugarcane became a lucrative cash crop for Australian farmers, the cane beetle became a pest so cane toads, native to Central and South America, were introduced to eat the beetles and protect the sugarcane.  Soon though, life in the sugar field must not have been sweet enough for the toads because they began hopping across the continent.  Cane toads are now present across most of the north and east coasts of Australia with the potential to continue spreading.  

Map of cane toad range as of 2009, curtsey of Australian Government Department of Sustainability, Environment, Water, Population, and Communities

Cane toads have poison glands behind their eyes which makes them dangerous to native Australian snakes and lizards tempted to eat them.  However, even massive public-involvement campaigns to  stop the spread of cane toads have failed.  The animal brought in to control a pest has now become a pest itself.

Although he suggested introducing elephants to the Australian continent, Bowman reported to other news outlets including the Australian Broadcasting Company that his primary intent is not to begin shipments non-native species tomorrow, but rather to start a conversation about alternative methods of controlling invasive species.  Bowman mentions alternative forms of Gamba grass control, including employing Indigenous rangers to burn the grass.  Yet, he concludes by stating, "The usual approaches to managing these issues aren't working.  The full spectrum of options needs to be canvassed in an open and honest way."  However, his dismissal of other methods for controlling Gamba grass that do not involve introducing more non-native species fails to acknowledge that those alternative methods have yet to be implemented in an effective, long-term manner.

A possible alternative method of preventing large bush fires is to intentionally start fires on days with weather conditions that will not promote a fire, such as high humidity and low wind.  These planned fires will reduce the amount of fuel in the area making any natural fire smaller and cooler.  Currently, most planned fires are designed to protect towns and cities from fire, not to control Gamba grass.  A rigorous fire regimen of prescribed burns might manage Gamba grass without the ecological complications of inviting more non-native species like elephants to the Outback.

The cautionary croak of the cane toad exemplifies the unintended consequences of introducing non-native species to the receiving ecosystem, but removing a species from its native environment might damage that ecosystem too.  African elephants are listed as a threatened species in the Endangered Species Act, which leads to the thought that in addition to the potential damage in Australia, reducing the number of elephants in their natural habitat won't be good for the elephants or for the savannahs that might miss them.

Generating a discussion about controlling pest organisms is commendable and as an expert in the biology of environmental change, Bowman's recommendations deserve sincere consideration.  His suggestion to re-introduce the dingo, Australia's native dog, has the potential to undo damage caused by population explosions of prey species (including rabbits) when dingos were hunted extensively, primarily due to cattle farmers' unfounded fears of dingos killing cattle.  But mixing suggestions of re-introducing native species with suggestions of introducing non-native species distracts from the primary focus of the discussion: how should humans try to mend the ecosystems we have broken?


  1. I know an old woman who swallowed a fly, and a cane toad, and an elephant...

    (She's dead, of course.)

  2. Check out Cane Toads: An Unnatural History. http://movies.netflix.com/Movie/Cane-Toads-An-Unnatural-History/70000977

    You never can quite tell if it's supposed to be a documentary or a comedy...

  3. The same ineffective strategy was implemented in the USA too: stink bugs were introduced to control the invasive Japanese ladybugs. I haven't seen a ladybug of any variety in years, but the stink bugs are EVERYWHERE now. If non-native introduction has never yet worked successfully, why do people keep proposing it?
    That said, it's going to be a heck of a lot easier to find every last elephant and ship them back to Africa when the gamba grass is gone, versus finding every last cane toad in a field.