Tuesday, February 12, 2013

Introduction of Invasive Species


By Tia Rose MSc. 

    The introduction of invasive species is characterized as an introduction of a non-native species that colonizes an area and spreads beyond that range, often negatively impacting the habitats economically, environmentally, or ecologically *1. The mechanisms by which new species are introduced to an environment, in today’s age, are largely anthropogenic. Human population growth coupled with the industrial and technological revolution, have expanded people to every corner of the earth.

    Natural species dispersal would occur through other means like wind, ocean currents, and by other animal dispersion by attaching to the coat or feathers or through indigestion and scat. Man can also act as a dispersion unit by accidentally carrying seeds of plants on their clothing and by the creation of mass transit via planes, trains, and automobiles. Air travel, in particular, has made this mechanism possible for species to disseminate their genes far and wide through the use of our vessels. Although, more commonly it is humans who have deliberately introduced and disseminated the genes of our most useful and favorite flora and fauna that has become such an issue. Some introduced species have been to the benefit of humans, such as agricultural crops like corn, wheat, and soy. Many, however, have purposely been introduced that have had no benefit to man and even worse, cause detriment to the environment. Two examples of species, connected with of anthropogenic introduction, that have been devastating to biodiversity are the introduction of the cane toad, Bufo marinus, into Australia as a biological control and the accidental introduction of the brown tree snake, Boiga irregularis, into Guam.


     The cane toad, Bufo marinus, was deliberately introduced to Australia from Hawaii in 1935 as a biological control in an effort to control beetle pests of sugar cane plants *2. The ‘whitegrub’ larvae of the French’s Cane Beetle, Lepidiota frenchi, and the Greyback Cane Beetle, Dermolepida albohirtum Waterh, stunted or killed the growth of sugar cane by eating the roots, wreaking havoc on the sugar cane industry in Australia *2. Once the cane toad was introduced to Australia, it not only did not control either of the cane beetle species, but with no natural predator to control its population, Bufo marinus quickly spread and began killing anything that tried to eat it. The speed with which the cane toad spread across the Northern Territory of Australia was astounding with an annual rate of progress that increased fivefold from the first introduction of the species *3.


     Heavily built, with dry warty skin, this amphibian is poisonous throughout its life cycle. Death from native species that ingest cane toads has caused undo biodiversity loss wherever they have established community populations. One study found a 45% decrease in freshwater crocodiles (Crocodylus johnstoni) following the arrival of cane toads *4. Though, little is known on the true impact the invasion of cane toads has caused on Australian flora and fauna as most of the impact studies were started well after the usurpation *4.




Speed of Invasion History *3


     In the case of the brown tree snake, Boiga irregularis, the loss of biodiversity is unbelievable. Accidentally introduced into Guam, most likely as a stow away on an aircraft sometime after World War II, the brown tree snake is thought to be responsible for the near complete extinction of native bird species there *5. The population of the snake didn’t begin rapidly spreading until after 1960. This could be due to the lag time often associated with introduced species (*6; *7; *8) or the possibility that humans continued to introduce them throughout the island to control the rat population *5. No matter the cause, this nocturnal arboreal snake has been blamed for hundreds of power outages, loss of domestic animals, and the extinction of the native bat and lizard population *5.


     In 1999 it was stated that ‘it may not be long before invasive species surpass habitat loss and fragmentation as the major engines of ecological disintegration’ *9. Today it is estimated that as many as 80% of ‘endangered species are threatened and at risk due to the pressure of nonnative species *10.   Invasive species are pushing the diversity of biological communities worldwide into a singular homogenized environment that lacks the variety necessary for a healthy ecosystem.


 



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Resources: Hawaii invasive species, Out of Eden: An Odyssey of Ecological Invasion,  ,Hawaii Invasive Species

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