The Economics of Controlling a Biological Invasion
1. Introduction
Throughout history the spread of plants, animals and other organisms has been governed by
natural ecological processes and has accompanied the movement of humans. As human beings have
become more mobile there has been an increase in the introduction of species to areas outside their native
habitat. Sometimes such introductions are harmless, or even beneficial. In other instances, introduced
species become invaders with few natural enemies to limit their growth.
The invasion of ecological systems by non-indigenous species is now recognized as a growing
global problem that imposes significant economic and ecological damages. In the United States alone,
the total costs of non-indigenous species have been estimated to be at least $137 billion per year
[Pimentel, et. al., 2000]. Approximately one-fourth of the value of the country 's agricultural output is
lost to non-indigenous plant pests or the costs of controlling them [Simberloff, 1996]. Invasive species
also cause significant ecological harm. They can alter ecosystem processes, act as vectors of disease, and
reduce biodiversity [Vitousek, et. al., 1996]. Worldwide, out of 256 vertebrate extinctions with an
identifiable cause, 109 are known to be due to biological invaders. In comparison, 70 such extinctions
are known to be caused by human exploitation [Cox, 1993]. It is estimated that forty percent of the
threatened or endangered species in the United States are at risk due to pressures from invading species
[The Nature Conservancy, 1996; Wilcove et. al., 1998].
Although the number of harmful invasive species in the United States is in the thousands
[Pimentel, et. al, 2000] a single invasive species can cause tremendous economic and/or ecological
damage. For example, the costs of controlling the zebra mussel (Dreissena polymorpha) in the Great
Lakes are expected to reach $5 billion in 2001 [USGS, 2000] while the Russian wheat aphid (Diuraphis
noxia) caused an estimated $600 million (1991$) in crop damages between 1987 and 1989 [OTA, 1993].
The invasion of Guam by the brown tree snake (Boiga irregularis) demonstrates the ecological harm an