ANAHEIM, CALIF. -- A few bad actors among the more than 30,000 non-indigenous species in the United States cost $123 billion a year in economic losses, Cornell University ecologists estimate.
"It doesn't take many trouble-makers to cause tremendous damage," Cornell University ecologist David Pimentel says of a list that runs from alien weeds (cost: $35.5 billion) and introduced insects ($20 billion) to human disease-causing organisms ($6.5 billion) and even the mongoose ($50 million ). (See accompanying list, "25 Unwelcome Visitors.") Aside from the economic costs, he adds, more than 40 percent of species on the U.S. Department of the Interior's endangered or threatened species lists are at risk primarily because of non-indigenous species.
Pimentel, who presented his findings today (Jan. 24, 1999) at the annual meeting of the American Association for the Advancement of Science (AAAS) in Anaheim, Calif., noted, however, that "most introduced species of plants, animals and microorganisms have become widely accepted and even beneficial participants in our lives."
The damage report, "Environmental and Economic Costs Associated with Non-indigenous Species in the United States" by Pimentel, a professor in Cornell's College of Agriculture and Life Sciences, and by Cornell graduate students Lori Lach, Rodolfo Zuniga and Doug Morrison, was presented in a AAAS session on environmental science and philosophy. The researchers also acknowledged that 98 percent of the U.S. food supply comes from such introduced species as wheat, rice, domestic cattle and poultry with a value of more than $500 billion a year.
However, even the introduced food sources have alien enemies, such as the mongoose, that was brought to Puerto Rico and Hawaii in the late 1800s, supposedly to kill rats in sugarcane plantations. The islands still have rats, but the mongooses are preying on native ground-nesting birds and on amphibians and reptiles that could, themselves, be beneficial for pest control. The extinction of at least 12 species of reptiles and amphibians in Puerto Rico and other islands of the West Indies is blamed on mongooses, which also carry the pathogenic organisms for rabies and leptospirosis.
Meanwhile, the United States has become the land of a billion rats, most of them the introduced Rattus rattus (also known as the European, black or tree rat) and Rattus norvegicus (variously called the Asiatic, Norway or brown rat). Rats on poultry farms and other farms number about 1 billion and each destroys grain and other goods worth $15 a year, Pimentel says. In urban and suburban areas of the U.S., there is roughly one rat for every human, causing fires by gnawing on electric wires, polluting foodstuffs and carrying diseases such as salmonellosis and leptospirosis.
Nor do cats and dogs escape the ecologists' scrutiny. According to Pimental:
-- America's 63 million domestic cats and 30 million feral cats are believed to kill some 200 million birds a year. At an estimated $30 a bird, that amounts to $6 billion a year in cat damage.
-- Dogs bite an estimated 4.7 million people each year, sending 800,000 patients to the emergency room, resulting in loss of life and approximately $30 million in medical costs. Wild dogs running in packs in Florida, Texas and other states cause an estimated $10 million a year in livestock losses, rivaling or exceeding the damage from wolves and other indigenous canines.
Like cats and dogs, many other introduced species seemed like a good idea at the time, Pimentel said:
-- Purple loosetrife (Lythrum salicaria) was introduced from Europe as an ornamental plant in the early 1800s. Loosestrife now invades wetlands in 48 states at an estimated cost of $45 million a year for control and loss of forage crops, crowding out 44 native plants and endangering the wildlife that depend on the native plants.
-- When the English sparrow (Passer domesticus) was intentionally introduced to the U.S. in 1853, it was supposed to control canker worms. Instead, the hardy little bird became a pest by eating crops, displacing some native birds and harassing others, and carrying 29 diseases that affect humans and domestic animals. And canker worms still bedevil gardeners.
"It's too late to send these organisms back," Pimentel said, noting that most of the non-indigenous species have arrived only in the last 70 years. "We will be lucky to control further damage to natural and managed ecosystems."
While policies and practices to prevent accidental or intentional introduction are improving, Pimentel told the AAAS meeting, "we still have a long way to go before the resources devoted to the problem are in proportion to the risks. We can only hope that environmental and economic assessments like this one will demonstrate that resources spent on preventing the introduction of potentially harmful non-indigenous species can be returned many times over in safeguarding our environment."
25 Unwelcome Visitors
(Annual economic costs of some introduced species in the United States ) From David Pimentel, Lori Lach, Rodolfo Zuniga and Doug Morrison, College of Agriculture and Life Sciences, Cornell University
Weeds in crops $29,000,000,000
Diseases in crops 23,500,000,000
Insects in crops 14,500,000,000
Weeds in forages, gardens, etc. 6,500,000,000
Human diseases 6,500,000,000
Plant diseases in gardens 3,000,000,000
Zebra mussels 3,000,000,000
Insects in gardens 2,500,000,000
Insects in forests 2,100,000,000
Insects in forests 2,100,000,000
Asiatic clam 1,000,000,000
Other plants 250,000,000
Elm disease 100,000,000
Green crab 44,000,000
Gypsy moth 22,000,000
Fire ants 10,000,000
Horses and burros 5,000,000
Reptiles and amphibians 604,000
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