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198 IGUANA  •  VOLUME 12, NUMBER 3  •  SEPTEMBER 2005 COMMENTARY

Across ecosystems and geographic regions, the rate of newly
detected biological invasions is increasing, and, in the case

of individual species, this increase is often exponential (Ruiz et
al. 2000, Ruiz and Carlson 2003, Fofonoff et al. 2003, Kraus
2003). Invasive alien species have become a real threat to our
environment and economy. The economic costs of invading
alien species in the United States alone come close to $120 bil-
lion per year (Pimentel et al., in press).

Harmful invasions of alien or non-indigenous species often
produce devastating impacts on agriculture, recreation, and nat-
ural resources (OTA 1993). They threaten biodiversity, habitat
quality, and ecosystem function and are now considered among
the greatest threats to native species in the United States
(Wilcove et al. 1998). In combination with other economic
activities, the rapid expansion of international trade, travel, and
transport have contributed significantly to the increasingly high
rate of species invasions. Also, unfortunately, “the pressures to
increase trade are currently greater than the pressures for pre-

caution in moving biological material across former barriers”
(Mooney and Hobbs 2000). The following discussion highlights
the links between this exponential increase and the unrestricted
trade of a growing global economy.

One of the by-products of international trade and travel is
the transportation of species beyond their natural geographic
range. A species that is not native to a particular ecosystem is

C O M M E N T A R Y

The Economic Roots of 
Species Invasions1

Jenny A. Ericson2

1 Adapted from “Economic Growth Forum,” Fisheries 30(5):30–33
(May 2005) and published with permission.

2 The author is an independent natural resource management con-
sultant currently working with invasive species on a federal govern-
ment contract. She can be contacted at riverine8@hotmail.com.

Opinions expressed are those of the author and may or
may not reflect those of the IRCF.

The House or Wall Geckos of Florida and other southern states actually represent a sequence of invasions that began with the Mediterranean Gecko
(Hemidactylus turcicus), which was followed by the Cosmopolitan House Gecko (H. mabouia, pictured), and even more recently by the Asian House
Gecko (H. frenatus). How these species will ultimately partition the available habitats remains to be seen.

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IGUANA  •  VOLUME 12, NUMBER 3  •  SEPTEMBER 2005 199COMMENTARY

referred to as alien, exotic, or non-indigenous. A subset of alien
species is considered invasive by virtue of their ability to cause
economic or environmental harm, or harm to human health
(Executive Order 13112). They generally exhibit characteristics
such as rapid growth rate, exceptional dispersal capabilities, large
reproductive output, and broad environmental tolerance.
Although naturally occurring movement of species has taken
place across the surface of the earth for hundreds of millions of

years, human activity has greatly increased the velocity of inva-
sion and, by dissolving temporal and spatial boundaries, has
enabled many species to relocate that would not normally have
had this opportunity. Most arrive in relation to human eco-
nomic activities, either intentionally or unintentionally.

Invasive species move along routes referred to as pathways.
Their movement is facilitated by vectors, the means by which a
species is moved, such as ships, planes, people, and other organ-
isms. Throughout history, cultures and civilizations have relied
on trade to improve relations and increase prosperity.
Archaeologists have found evidence of human-assisted move-
ment of species by way of seafaring trade connecting continents
early in history. Among the first specialized sailors and mer-
chants were the Phoenicians (ca. 3000 B.C.) who traded articles
such as Lebanese cedar and processed dyes (Cameron 1997).
Greek sailors and merchants traded basic storable foodstuffs,
such as grain, grapes, olives, wine, and oil. During Roman times,
sea trade existed between India and Egypt; and, as early as the
sixth century, the Vikings were exchanging honey, fur, weapons,
and slaves for Arabian silver, which has been found as far west
as North America (Het Huis van de Aarde Museum 2005).

Between the eighth and fifteenth centuries, Indian
Diaspora and Far East trade routes were used not only for eco-
nomic expansion, but also for the expansion of religion. By the
first half of the seventeenth century, the Netherlands had estab-
lished a fully global trading network (Brummett and Edgar
1999).

The popularity of Red-eared Sliders (Trachemys scripta elegans) in the pet trade and the resultant and maybe inevitable escapes and releases have led
to wild populations in many areas where the species is not native, with negative effects on native turtles and yet-to-be evaluated impact on native
invertebrates and aquatic vegetation (see also Newsbriefs, p. 216). 

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Introductions of mammalian herbivores, such as these burros on St.
Eustatius, alter vegetative communities in ways that cannot be predicted,
often with catastrophic effects on native herbivores such as iguanas. 

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200 IGUANA  •  VOLUME 12, NUMBER 3  •  SEPTEMBER 2005 COMMENTARY

Today, transportation of people and cargo via ships and
planes has become fast, efficient, and frequent. Increased speed
and efficiency of transport enables international trade and feeds
aspirations for economic globalization and growth. One ship-
ping company alone can maintain a global network of shipping
lines. For example, in 2004, the shipping company Maersk
Sealand advertised itself as one of the largest liner shipping com-
panies in the world with over 300 shipping vessels and 950,000
containers traveling around the globe, with feeder vessels, trucks,
and dedicated trains available for door-to-door service
(www.maersksealand.com).

With increases in total volume of trade and the speed and
frequency of transportation and delivery come greater risks of
introduction, both intentional and unintentional. For example,
larger numbers of products bring greater opportunity for unin-
tentional introductions referred to as “hitchhikers,” organisms
that attach themselves to the product itself, such as insects on
plants, or that exist within the transportation medium, such as
ballast water. As shipping technology continues to improve,
ships take less time to traverse greater distances, which means
mortality decreases and organisms that might have once died
while en route for a few weeks or a month may now have a bet-
ter chance of survival, given that the journey has been shortened
to a number of days. As the rate of non-indigenous, potentially
invasive, species introduction accelerates, trade itself begins to
look more and more like a sort of “metavector,” comprising
numerous, individual, yet associated, vectors.

International trade currently represents a growing share of
the U.S. economy. Import volume increased from $40 billion in
1991 to around $100 billion in 2001, more than doubling in a
10-year period (Bureau of Transportation Statistics 2002). Some
predict that global trade will double again by the year 2020. This
international trade facilitates the intentional and unintentional
transport of biological organisms around the world.

Approximately 42% of the plants and animals federally
listed as threatened or endangered species are at risk because of
alien and invasive species (Pimentel et al., in press). The

National Invasive Species Council’s (2003) working group on
pathways identifies three major categories of pathways for the
introduction of alien and invasive alien species: (1) transporta-
tion, (2) living industry, and (3) miscellaneous. Within the cat-
egory of transportation, pathways include the movement of
water (e.g., ballast water, sediments, and dredge spoil materials),
items used in transport (e.g., vehicles and ships), and “hitchhik-
ers,” organisms attached to vehicles, ships, or materials attached
to them.

Perhaps the most notorious example of a species entering
through a transportation pathway is the Zebra Mussel (Dreissena
polymorpha). This invasive species entered the United States
through the St. Lawrence Seaway as planktonic larvae, probably
in the ballast water of a bulk cargo vessel coming from a Black
Sea port (Holeck et al. 2004). Since their discovery in 1988,
Zebra Mussels have spread from the Hudson River in the east
to Oklahoma in the west, and from Ontario and Quebec in the
north to Louisiana in the south. Zebra Mussels are small bivalves
that cluster in colonies of hundreds of thousands per square yard
and clog the openings of underwater pipes, often closing them
off altogether.

Additionally, invasions are facilitated by the mail, internet,
and overnight shipping companies. In particular, the internet is
a very difficult pathway to control. Although recognized as a fed-
erally-prohibited weed, Giant Salvinia (Salvinia molesta) is still
available for purchase on the internet.

Within the council working group’s category of “living”
industry, pathways include the food industry and non-food
industries transporting animals and other organisms, such as the
pet trade, research, and public education and enjoyment such as
zoos and public aquariums. Through any of the living industry
pathways, species can be intentionally released, escape, or hitch-
hike with people, products, and services. The plant trade is often
a vehicle for species introduction through nurseries and pet stores.

Water hyacinth, an example of a highly invasive aquatic
species, began charting its course around the globe in 1884. This

Alien carnivores, such as this Jamaican mongoose (Herpestes javanicus),
originally imported from India to control rats in the sugar cane fields,
were subsequently introduced to many other West Indian islands and
to the major Hawaiian islands. Among the unintended consequences
were little impact on rat populations and dramatic declines in popula-
tions of ground-nesting birds and diurnally active terrestrial reptiles.

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Because of their sensitivity to desiccation and exposure to salt water,
amphibians are rarely effective invasives. Nevertheless, some exceptions
exist. Cuban Treefrogs (Osteopilus septentrionalis) are native to Cuba and
may have expanded their range naturally to the Bahamas, Cayman
Islands, and possibly to Florida. However, increasing numbers of pop-
ulations are being established, mostly due to inadvertent “hitch-hiking”
with exotic, tropical plants from southern Florida that are destined for
resorts to meet tourists’ expectations of what the tropics should be like. 

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IGUANA  •  VOLUME 12, NUMBER 3  •  SEPTEMBER 2005 201COMMENTARY

plant originally came from the Amazon Basin in South America
and is today a serious pest in North America, tropical Africa, and
Southeast Asia. In certain parts of tropical Africa, riverboat trans-
port has become impossible because this aquatic weed has com-
pletely blocked entire river systems. The control cost to seven
African countries runs about $20–50 million per year (McNeely
et al. 2003).

The council working group’s category of miscellaneous
pathways includes interconnected waterways for aquatics or
interconnected landmasses for terrestrial organisms. One exam-
ple of introduction by interconnected waterways is the Sea
Lamprey (Petromyzon marinus), which is native to the Atlantic
Ocean. It entered the Great Lakes through the Hudson River
and the Welland Canal in 1829 and was later discovered in Lake
Erie in 1921 (Mooney and Hobbs 2000). The Sea Lamprey
attaches itself to other fish and with its suctorial mouth extracts
blood and other body fluids.

In order to address the problem of biological invasions,
some important legislation has been passed. In 1990, the
Nonindigenous Aquatic Nuisance Prevention and Control Act
(NANPCA) called for a national program to prevent and
respond to problems caused by the unintentional introduction
of nonindigenous aquatic species into U.S. waters, and it estab-
lished the multi-agency Aquatic Nuisance Species Task Force to
carry out its mandates. A reauthorization took place in 1996 in
the form of the National Invasive Species Act (NISA). Currently
a second reauthorization, the National Aquatic Invasive Species
Act (NAISA), is under review by Congress. The latter would
require a standard for ballast water management and appropria-
tion of funds for the National Oceanic and Atmospheric
Administration, the U.S. Geological Survey, and the
Smithsonian Institution to establish baselines and invasion rates,
as well as improved tools for early detection. It also will focus on
rapid response to incipient infestations, establish a separate fund
administered by the U.S. Fish and Wildlife Service to assist states
to respond to newly detected species. It would allocate funding
for establishing a screening mechanism for intentional introduc-
tions. It also will encourage the examination of new pathways
besides the historical focus on ballast water. Finally, it will man-
date more and better research on the topic. Although nearly 30
federal acts and executive orders pertain in some way to invasive
species, and some address terrestrial forms (e.g., the Brown Tree
Snake Control and Eradication Act of 2004), none, individually
or collectively, effectively addresses problems caused by terrestrial
invasives in the same fashion as NAISA does for aquatics.

Efforts concerned with prevention, specifically risk identi-
fication and assessment, further research on pathways, and con-
tinued exploration of avenues available through regulation, must
continue. We need to strengthen outreach at all levels and con-
tinue to support research specifically in invasion ecology. For
management of invasive species at the field level to be success-
ful, we must encourage a greater understanding of early detec-
tion/rapid response, control and management, and restoration
techniques.

Invasive species have been recognized as one of the most
significant drivers of environmental change worldwide — and
biological invasions are facilitated by the increasingly expanding
network of commercial highways underlying international trade,
travel, and transport. We must address these pathways. However,
even if urgent measures are taken, the number of species inva-
sions in the United States will probably continue to increase in
conjunction with the growth of the economy and the sectors
that constitute or represent pathways for invasive species.

References
Brummett, P., R. B. Edgar, N. J. Hackett, G. F. Jewsbury, A. M. Taylor, N.

M. Bailey, and T. W. Wallbank. 1999. Civilization Past and Present. 9th

ed. Longman Publ. Grp., White Plains, New York (http://occawlon-
l ine .pearsoned.com/bookbind/pubbooks/brummett_awl/
chapter20/deluxe.html).

Bureau of Transportation Statistics. 2002. Value of U.S. imports and exports.
U.S. Department of Transportation, Washington, D.C.
(www.bts.gov/publications/transportation_indicators/decem-
ber_2002/Economy/html/Value_of_US_Imports_and_Exports.html).

Cameron, R. 1997. A Concise Economic History of the World: From Paleolithic
Times to the Present. Oxford Univ. Press, New York.

Czech, B., P. R. Krausman, and P. K. Devers. 2000. Economic associations
among causes of species endangerment in the United States. Bioscience
50:593–601.

Fofonoff, P. W., G. M. Ruiz, B. Steves, and J. T. Carlton. 2003. In ships or
on ships? Mechanisms of transfer and invasion for nonnative species to
the coasts of North America, pp. 152–182. In: G. M. Ruiz and J. T.
Carlton (eds.), Invasive Species: Vectors and Management Strategies. Island
Press, Washington, D.C.

Het Huis van de Aarde Museum. 2005. Viking Trade Routes: Arabian Coins
in the Viking World. The Netherlands (www.huisvandeaarde.nl/ e-index-
2fr.htm).

Holeck, K. T., E. L. Mills, H. J. MacIssaac, M. R. Dochoda, R. I. Colautti,
and A. Ricciardi. 2004. Bridging troubled waters: Biological invasions,
transoceanic shipping, and the Laurentian Great Lakes. BioScience
54:919–929.

Kraus, F. 2003. Invasion pathways for terrestrial vertebrates, pp. 68–92. In: G.
M. Ruiz and J. T. Carlton (eds.), Invasive Species: Vectors and Management
Strategies. Island Press, Washington, D.C.

McNeely, J. A., L. E. Neville, and M. Rejmanek. 2003. When is eradication
a sound investment? Conservation Practice 4:30–313.

Mooney, H. A. and R. J. Hobbs (eds.). 2000. Invasive Species in a Changing
World. Island Press, Washington, D.C.

National Invasive Species Council. 2003. Invasive Species Pathways Team Final
Report. National Invasive Species Council, Washington, D.C. (www.inva-
sivespecies.gov).

OTA (Office of Technology Assessment). 1993. Harmful Non-indigenous
Species in the United States. U.S. Congress, OTA. U.S. Govt. Printing
Office, Washington, D.C.

Pimentel, D., R. Zuniga, and D. Morrison. In Press. Update on the environ-
mental and economic costs associated with alien species in the United
States. Ecol. Econ.

Ruiz, G. M., P. W. Fofonoff, J. T. Carlton, M. J. Wonham, and A. H. Hines.
2000. Invasion of coastal marine communities in North America:
Apparent patterns, processes, and biases. Ann. Rev. Ecol. Syst.
31:481–531.

Ruiz, G. M. and J. T. Carlton. 2003. Invasion Vectors: A Conceptual Framework
for Management Strategies. Island Press, Washington, D.C.

Wilcove, D.S., D. Rothstein, J. Dubow, A. Phillips, and E. Losos. 1998.
Quantifying threats to imperiled species in the United States. BioScience
48:607–615.



202 IGUANA  •  VOLUME 12, NUMBER 3  •  SEPTEMBER 2005 COMMENTARY

Action Alert!     Action Alert!     Action Alert!

If you have “non-native” weeds, grass, trees, or shrubs on
your property (and everyone does) you’re in trouble.

Under “invasive species” provisions currently sitting in the
Senate’s version of the transportation bill, your property
could quickly become the target of radical environmental-
ists and federal bureaucrats. The bill’s name is the “Safe,
Accountable, Flexible and Efficient Transportation Equity
Act” or SAFETEA 2005 (*please note* that it does not yet
have a bill number).

It is vitally important that you call both of your
Senators this week, and next week, and tell them to
DEMAND that any invasive species provisions be stripped
from the SAFETEA bill. SAFETEA could come up for a
vote before the full Senate at ANY TIME!

**Call the Senate Switchboard at (202) 224-3121 and sim-
ply ask for your Senators by name.**

Currently, the SAFETEA act contains provisions to “mini-
mize invasive species.” This is the foot in the door to federal
control of ALL so-called “invasive species” — something
that the greens openly covet. Under the Senate version of
SAFETEA, the federal government will dictate to the states
what types of grasses and plants are allowed to be planted
next to roads. This has nothing to do with science or the
environment. This is about LAND CONTROL and
MONEY FOR RADICAL GREEN GROUPS.

**Call your Senators at (202) 224-3121 and tell them:
NO INVASIVE SPECIES PROVISIONS 

in the transportation bill!**

Imagine the Endangered Species Act on steroids. Now mul-
tiply its devastating effect on property rights one-hundred
fold. That should give you a pretty good idea of what “inva-
sive species” legislation will mean for property owners in
every state, county, and city in this nation. “Invasive
species” is the radical greens’ key to controlling every square
inch of land in the United States. And SAFETEA is the just
the beginning.

This nightmare all began when Bill Clinton signed
Executive Order 13112 in 1999, creating an “Invasive
Species Council” to monitor and control “alien species.”
What are alien species? According to Clinton’s Order, “alien
species means, with respect to a particular ecosystem, any
species, including seeds, eggs, spores, or other biological
material capable of propagating that species, that is not
native to that ecosystem.” Most agricultural crops and ani-

mal species clearly fall within the definition of “alien.”
Domesticated pets, many houseplants, and Kentucky blue-
grass used in most lawns and golf courses are already
defined as alien species. Indeed, this is all the greens and
their allies in the federal government need to control all
land in the U.S.

Think the invasive species monster can’t get any worse?
It already has. In 2001, the Invasive Species Council issued
a management plan that states: “Council member agencies
will work with the Global Invasive Species Programme
(GISP) and other relevant bodies to expand opportunities
to share information, technologies, and technical capacity
on the control and management of invasive species with
other countries, promoting environmentally sound control
and management practices.” And just what is the Global
Invasive Species Programme? A quick trip to the GISP web-
site reveals it is: The United Nations Environmental
Programme (UNEP), The United Nations Environmental,
Scientific, and Cultural Organization (UNESCO), The
Convention on Biological Diversity, The Nature
Conservancy, The International Union for the Protection of
Nature, [and] DIVERSITAS: An International Programme
of Biodiversity Science (another UNESCO project).

Invasive species legislation opens the door to federal
and international control over private property in the
United States. And that’s why greens in the Senate are try-
ing to sneak it into the federal transportation bill — with-
out ANY proper debate. We are running out of time.
Contact your Senators TODAY, TOMORROW, AND
NEXT WEEK. The House version of the transportation
bill has already passed and thankfully does NOT include
any invasive species language. But the Senate version
(SAFETEA 2005) DOES! Once again, the House is on the
right track and the Senate is out in left field. ACT NOW!

**Action to Take**
Call both of your Senators and tell them to DEMAND
that any and all “invasive species” provisions are
REMOVED from the Senate transportation bill
(SAFETEA). Call the Senate Switchboard at (202) 224-
3121 and ask for your Senators by name.

***PLEASE SEND THIS URGENT ALERT TO AS
MANY PEOPLE AS POSSIBLE***

URGENT: 
Invasive Species Legislation in Highway Bill!1

March 30, 2005

1 From the American Policy Center (http://www.americanpol-
icy.org/sledgehammer/species.htm); the APC promotes its
website as the “Property Rights and Back-to-Basics
Education Grassroots Internet Headquarters.”



IGUANA  •  VOLUME 12, NUMBER 3  •  SEPTEMBER 2005 203COMMENTARY

For many years, governments and citizens in Michigan
and throughout the Great Lakes Basin have been bat-

tling a notorious invader – the Zebra Mussel. These small
mollusks invaded the Great Lakes in the 1980s, quickly
multiplied and spread across the region, clogging water
intake pipes and creating problems for boaters who have to
spend time and money cleaning hulls. Last summer, a vora-
cious fish known as the Northern Snakehead became a
media celebrity and a serious threat to Maryland water-
ways. This predator wipes out native fish and, once it is
done feeding in one pond, it literally gets up and crawls
across land to the next one. These are only two examples of
“invasive species” – animals and plants that are introduced,
take hold and multiply in ecosystems where they don’t have
any competition, causing tremendous economic and envi-
ronmental harm.

If you polled Americans as to what the most pressing
economic and environmental issues are, dealing with inva-
sive species probably wouldn’t make the list. But consider-
ing the economic and environmental threats they pose to
our nation, attention must be paid to invasive species. For
example, recent studies have estimated that Zebra Mussels
have cost governments and utilities in the Great Lakes
region more than $1 billion since the late 1980s. On an
environmental level, invasive species are now recognized as
the No. 2 threat to endangered species, as they often com-
pete for food and destroy the habitat of other native plants
and animals.

Congress must act to combat this threat. That’s why I,
along with Senator Carl Levin and others, have sponsored
a comprehensive legislative package (H.R. 1080 & 1081
and S. 525) to do just that. One central theme drives our
effort – “an ounce of prevention is worth a pound of cure.”
If we spend millions preventing aquatic invasive species
from entering our waters, we will avoid spending billions
trying to control and manage them once they are here. Our
legislation does three overarching things fitting with this
theme.

First, this legislation takes major strides forward in
managing the shipping industry, which is responsible for
(unintentionally) bringing most of the aquatic invasive
species into our waters through ships’ ballast tanks. The leg-
islation contains provisions that require shippers to ensure
that they are using best management practices, and, most
importantly, treat ballast water so that species are killed
before ballast water is dumped into our waterways. This is

the most effective way to prevent the next Zebra Mussel
from entering our waterways and wreaking economic and
environmental havoc.

Second, we will, for the first time, establish a screen-
ing program to look at the intentional introduction of new
plants and animals into the United States. People have been
bringing new species into America since before our nation
was created. The rate of these introductions has increased
dramatically over the past 50 years because of global trade
and efficient and fast transportation systems. Under current
law, we take no action until we know that a species is harm-
ful, which is too late. This legislation changes that burden
by allowing federal agencies to screen for potential “bad
actors” and prevent the next Northern Snakehead from
being imported into the United States.

Finally, we establish a comprehensive research pro-
gram, which was sorely lacking in previous legislative efforts
to deal with invasive species. I’m taking the lead on this part
of the legislative effort, because when I looked at the under-
lying law, it became clear that research was simply an after-
thought. This explains why so much of the invasive species
management program has been stalled for years. Good sci-
ence must underpin management decisions if these deci-
sions are going to be considered credible to the outside
world.

It is time to change our strategy in dealing with
aquatic invasive species. It is time for Congress to realize
that this threat continues to grow and will not go away
unless we act. It is time for Congress to move this legisla-
tion forward. Invasive species don’t recognize or respect
political boundaries or timelines and they are arriving here
even as you read this today.

Invasive Species Legislation1

Congressman Vernon J. Ehlers2

United States House of Representatives
Washington, D.C. 20515-2203

1 Adapted from an op-ed piece for Business Direct Weekly, March
2003.

2 The Honorable Vernon J. Ehlers, United States House of
Representatives, serves Michigan’s third district. He serves on
the following committees: House Committee on Education and
the Workforce, Subcommittee on 21st Century
Competitiveness, Subcommittee on Education Reform; House
Committee on House Administration; House Committee on
Science, Subcommittee on Energy, Subcommittee on
Environment Technology and Standards (Chair); House
Committee on Transportation and Infrastructure,
Subcommittee on Aviation, Subcommittee on Water Resources
and Environment; Joint Committee on the Library of Congress.




