The Convention on Biodiversity identifies invasive species as any foreign species that threatens the balance of an ecosystem through its introduction and proliferation (Born 2004). Such non-native species generally arrive in one of two ways: unintentional introduction (such as microorganisms transported in a ship’s ballast water) and intentional introduction (such as nursery plants or food crops).
The introduction of invasive species can result in the extinction of local species and irreparable changes to the habitat and biodiversity of invaded ecosystems (Chornesky and Randall 2003). The Convention on Biological Diversity lists invasive species as one of the direct drivers of biodiversity loss (CBD 2007). These species lead to the killing or crowding out of native species through predation, parasitism, disease, and competition (Chornesky and Randall 2003). They also alter ecological processes such as the water, nutrient, and energy cycles, thus completely changing how ecosystems function (Union of Concerned Scientists 2007). In addition, invasive and native species can mate to form hybrid species, which can potentially displace the native species, leading to a loss of stability among the native population and eventual extinction (Cleeland and Mooney 2001).
The economic impact of invasive species is derived from direct and indirect costs. Direct costs are those related to controlling the spread of invasive species, such as the use of pesticides applied in an attempt to contain the spread of pests. Indirect costs relate to the ecosystem services lost through such destruction (Global Invasive Species Program 2007). Worldwide, billions of dollars are spent annually as a result of invasive species (Invasive Species Specialist Group 2007).
Invasive species spread disease that can be devastating to human health (National Environmental Coalition on Invasive Species 2004). Increased transportation and accessibility have allowed for new interaction between diseases and human hosts. Many non-native species can act as reservoirs for disease, including insects, rodents, and birds, which carry diseases such as yellow fever and malaria. More recently, the West Nile Virus that spread across North America and was carried by non-native mosquitoes. Other social concerns that stem from invasive species include food security and water depletion, which are significant concerns in developing countries (Global Invasive Species Program 2007).
Three principle factors contribute to the expansion of invasive species: global environmental change, chemical and physical alterations of ecosystems, and increased globalization (Global Invasive Species Program 2007). Environmental changes, such as nitrogen deposition, carbon dioxide accumulation, and changes in temperature and rainfall, allow species to thrive in previously unsuitable habitats (Chornesky and Randall 2003). Chemical and physical changes are brought about by human interaction with habitats: pesticide resistance allows insects to spread, and habitat destruction, such as forest clearing, also promotes the introduction of new species into the area (Chornesky and Randall 2003). In addition, mobility and technology contribute to the elimination of natural barriers between habitats (Globalization and Invasive Alien Species 2007).
Global trade has become the single largest factor in the worldwide spread of invasive species by means of ships, planes, and railroads (Bright 1999). Environmental disruption has increased as transportation technology has allowed a amplified level of global trade. The rate at which this problem is occurring makes controlling it very difficult, especially since there are no concrete national or international regulatory mechanisms in place (Bright 1999).
Invasive species are also closely connected with climate change. Biological changes caused by heightened levels of carbon dioxide and variations in temperature and precipitation patterns will have major impacts on the distribution and population levels of species, in addition to the composition and relationships between species in ecosystems (Chornesky and Randall 2003). Because the spread of invasive species often occurs at the international level, it must be addressed with innovative and well-enforced international policy. Invasive species present a global challenge, and as contributing factors such as international trade and mobility increase, international regulations will be increasingly necessary to limit the further introduction and spread of invasive species.
Bright, Christopher. “Invasive Species: Pathogens of Globalization.” Foreign Policy 116 (1999): 50-64. JSTOR. 06 Feb. 2007.
Chornesky, E. A., and J. M. Randall, The Threat of Invasive Species to Biological Diversity, Annals of the Missouri Botanical Garden, 90, 67-76, 2003.
Cleeland, E. E., and H. A. Mooney, Evolutionary Impact of Invasive Species, Proceedings of the National Academy of Sciences of the United States of America, 98, 5446-5451, 2001.
Convention on Biological Diversity. “Invasive Alien Species.” Programmes and Issues.http://www.cbd.int/programmes/cross-cutting/alien/ (accessed 18 December 2007).
Globalization and Invasive Alien Species, http://odin.dep.no/archive/udvedlegg/01/04/glob1064.pdf, (accessed 03 February 2007).
Invasive Species Specialist Group. “The Invasive Species Problem”. 25 March 2004. The World Conservation Union. http://www.issg.org/#Invasives. (accessed 06 Feb. 2007).
National Environmental Coalition on Invasive Species. “America’s Invasive Species Problem.” 2004.
http://www.ucsusa.org/assets/documents/invasive_species/the_problem.pdf 2004. (accessed 10 December 2007).
The Global Invasive Species Program. 2003. http://www.gisp.org/. (accessed 03 February 2007).
Born, Wanda, Felix Rauschmayer, and Ingo Brauer. “UFZ-Discussion Papers.” July 2004.http://www.ufz.de/data/ufz-disk7-20041828.pdf. (accessed 04 February 2007).
Union of Concerned Scientists. “Invasive Species.” 24 May 2007. http://www.ucsusa.org/invasive_species/. (accessed 06 February 2007).