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There are currently 50,000 non-native species in the United States. Many of these alien species have a positive impact on our economy (i.e. wheat, rice, cattle, poultry, etc.), however, a small fraction of these species have become aggressively invasive in our ecosystems. These aggressive invaders cause significant economic damage due to crop loss, control efforts, recreation losses, damage to structures, etc. There are also significant environmental costs due to invasive species such as loss of biodiversity, damage to threatened and endangered species, habitat destruction, and loss of aesthetics. The table below (adapted from Pimentel et. al. [2004]) displays the number of non-indigenous species per taxa and the economic cost associated with select invasive species. Pimentel found that the United States incurs a total of approximately $120 billion/year in damages associated with invasive species.
Taxa
# of Non-indigenous Species in US
Cost (millions of dollars)
Plants
25,000
Purple loosestrife
45
Aquatic weeds
110
Crop weeds
27,000
Weeds in pastures
6000
Mammals
20
Feral pigs
800.5
Fish
138
5400
Arthropods
4500
Imported fire ant
1000
Formosan termite
1000
Gypsy moth
11
Crop pests
14,400
Forest pests
2100
Mollusks
88
Zebra mussel
1000
Asian clam
1000
Microbes
20,000
Forest plant pathogens
2100
Excerpted from Pimentel et. al. (2004).
Resources:
Pimentel, D., Zuniga, R. and Morrison, D. 2004. Update on the environmental and economic costs associated with alien-invasive species in the United States.
Ecological Economics.
52: 273-288.
Pathways of Invasion
Invasive species often enter their non-native environment through anthropogenic activities. There are two ways that a species is introduced through a man-made pathway: intentional transportation of species from one location to another, or unintentional transportation of species as a by-product of the movement of people and goods. There are three major categories of man-made invasion pathways, which include transportation, living industries, and miscellaneous activities. The diagram below (adapted from The Invasive Species Pathways Team: Final Report) depicts the three main categories of invasion pathways and their associated sub-pathways.
Figure adapted from the Invasive Pathways Team: Final Report (2003)
by the National Invasive Species Council and the United States Department of Agriculture.
