Environmental consequences and economic costs of alien species - Invasive Plants: Ecological and Agricultural Aspects - page 241

Environmental consequences and economic costs of
alien species
David Pimentel
Department of Entomology, Systematics & Ecology, College of Agriculture and Life Sciences,
Cornell University, 5126 Comstock Hall, Ithaca, NY 14853, USA
Introduction
Assessing the environmental damage and loss of biodiversity due to alien spe-
cies invasions worldwide is complicated by the fact that only 1.5 million spe-
cies of the estimated 15 million species on earth have been identified and
described. The total number of introduced species in the United States is esti-
mated to be more than 50,000 species [1]. More than 120,000 species of
plants, animals, and microbes have invaded just six nations studied (United
States, United Kingdom, Australia, South Africa, India and Brazil) and these
are causing enormous ecological and economic damage and control costs [2].
Given the number of species that have invaded these six nations, it is esti-
mated that nearly 500,000 alien species have been introduced into the modi-
fied ecosystems on earth. Many introduced species, such as corn, wheat, rice,
plantation forests, domestic chicken, cattle, and others are beneficial and now
provide more than 99% of the world food supply with a value of more than $5
trillion per year [3]. These non-indigenous crop and livestock species origi-
nated in various geographic regions of the earth (Tabs 1 and 2), such as the
chicken from South Eastern Asia (Tab. 2). Other successful uses of alien spe-
cies have been landscape restoration (Norway maple), biological pest control
(valelia coccinelid beetle), sport (carp), pets (dogs and cats), and food pro-
cessing (yeasts). In the US the introduced species provide a value of approxi-
mately $800 billion per year [3]. However, alien species are known to cause
major economic losses in agriculture, forestry, and several other segments of
the world economy; they also negatively impact ecological integrity [1].
The low diversity of world crops (0.006% of the plant species) and world
livestock (0.1% of mammal species) presents the benefit of increased effi-
ciency, but also serious risks such as increased vulnerability to diseases and
invasive species. Increased biodiversity would offer some natural protection to
crops and livestock from alien species including disease pathogens. Especially
in need of protection are pollinators that are essential for about one third of
US and world crops. Each year US port inspections find 13,000 exotic plant
diseases while checking only 2% of incoming freight. Both crops and live-