Trade, Colonization & Invasive Species: How Human Travel Affects the Environment

Peter Brennan

            As Humans developed the technologies to travel, to carry themselves to new places through trade, exploration and colonization, they caused changes to those environments, some more debilitating than simply increased consumption.  It is clear that by simply increasing our sphere of influence through travel, we do more efficiently collect, distribute and consume new resources, affecting new environments.  However, in some cases the effects of human travel to new environments have caused unforeseen environmental effects with more threatening consequences.  The cultural constructs of trade and colonization, mechanisms of human travel themselves, have been largely responsible for the introduction of many invasive species into unprepared endemic environments.  Invasive species have stressed environments, unprepared for their presence, in many unique ecosystems like Australia, where the human colonization both intentionally and accidentally introduced a myriad of foreign animals.  A serious environmental concern with these invasive species, which tend to pressure native species into extinction, is their threat to local and global biodiversity.  Biodiversity is important for an ecosystem to survive periods of environmental stress, and its destruction has potentially devastating effect on the environment. 

            The unintentional introduction of invasive species to endemic ecosystems has been largely facilitated by vessels of trade traveling around the world.  The introduction of invasive species is not always related to human activity.  However, many are as these species must gain a foothold in an unfamiliar new environment with low populations and few mates before they can display their dominant and invasive traits.  The survival of this invasive species often benefits from repetitive introduction patterns associated with human activities like trade ships.  There were certain traits common to these species which allowed them to better survive in new environments.  Fast growth, rapid reproduction and a life cycle which could adapt to a new climate were generally helpful traits, and can be found in many species of the mammals and plants which disrupt the Australian ecosystem.

            Whenever humans have colonized new environments there have been many cases of intentional introduction of a harmful invasive species.  In this context, I am not interested with the relationship between any indigenous humans and the foreign colonizers, but with indigenous flora and fauna, and the colonizer’s foreign species.  These types of introductions can generally be classified as being undertaken by colonizers to “feel more at home” in a foreign environment.  For example, in North America, English colonists formed an Acclimation Society which repeatedly released European birds into the Northeast until they thrived, wiping out native bird species.  In this case, as in the accidental cases, we see that an invasive species is given a chance to thrive by repeated human introduction.  A large number of examples of invasive species introduction can be found in Australia, most notably the Rabbit.  The rabbit was first brought to Australia with the First Fleet in 1788, which established the British convict colony.  However, the first surviving group of rabbits has been traced back to a farm in Victoria belonging to Thomas Austin, where he released 24 rabbits in 1859 for hunting.  Within ten years these 24 rabbits had grown to 2 million, and by 1900 had spread across the entire nation.  The rabbits ravaged the abundant populations of vegetation, driving many species of flora into extinction and causing erosion problems.  It is estimated that about one eighth of mammalian species in Australia since 1700 are now extinct, predominantly due to resource competition with rabbits.  The abundance of rabbits spawned many government-sponsored programs to reduce their numbers.  In 1950 Myxomatosis, a rabbit disease which was fatal in 99% of cases, was released into the rabbit population.  After dropping the population from 600 to 100 million, genetic resistance allowed the population to stabilize to 200-300 million by 1991. A second virus known as Rabbit Calicivirus, or Rabbit Hemorrhagic Disease was released in the last decade, but was much less effective, being fatal in only 60% of the cases.  Many other invasive species have come to settle in Australia, leaving about half a million camels wandering in the desert and feral cats everywhere.  At times one invasive species has been introduced to combat an early species, often to disastrous effect.  The Cane Toad was introduced to destroy the Cane Beetle, which had been ravaging sugar cane crops.  Instead, the Cane Toad ate anything and everything else.  It turned out that its preferred food source, given a choice like the one Australia’s ecosystem provided, was not beetles.  In another, more recent, case the Latana Bug from South America was introduced to eat the Latana Tree.  The bug turned out to be quite the vegetarian, eating many other indigenous trees and causing farmers great distress.  Human introduction of invasive species through travel, whether intentional or not, has rarely had anything but devastating effects, especially in destroying biodiversity.

            To understand the value of biodiversity we must understand that in a complex ecosystem we may not see or notice every task in the chain of life, but each task is necessary.  Every species performs or contributes to some ecological function, such as soil enrichment, pollination, waste decomposition, water and air purification, or maintaining the water tables and climate.  Many scientists believe that a more diverse ecosystem is better able to withstand periods of environmental stress.  Biodiversity makes the ecosystem more adaptable to environmental change, similar to how genetic diversity makes the body more adaptable to change.  For an example of its useness, imagine modern agricultural food supplies, bred and selected for maximum yield.  Most of our edible vegetation has very limited biodiversity.  If some disease were to attack crops, as happened in the Irish Potato Famine, there would be no resistant species left surviving.  Many medications, like quinine, taken from the Cinchona Tree and used to treat malaria, are taken from rare unique ecosystems.  Over 70% of promising anti-cancer medications are derived from tropical rainforest plants.  Obviously the potential resources contained in a diverse ecosystem are worth preserving fro their own value.  Essentially, more adaptable and homogenized human-selected species dominating defenseless endemic species in environments around the world, threatening global biodiversity, is not good for the environment or humanity.

            Human travel, especially through colonization and trade, has allowed and encouraged invasive species to propagate through the world, destroying the most unique ecosystems, and global biodiversity.  This threat to biodiversity is increasingly acute given the current climate of global warming, new diseases of rainforest origin, and biological warfare.  During periods of stress caused by any of these factors, a diverse ecosystem would most certainly be helpful.  If human travel continues to threaten biodiversity, perhaps some effort should be made to lessen our reach, and make this small world a little bigger.


This article was written using the Inavasive Species pages on

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last updated 3/29/06