LINKS: U.S. Geological Survey Interdisciplinary Research Fact Sheets

# Imperiled Species and Communities Threatened by Invasive Species

## Introduction

The impacts of invasive species on our economy and ecosystems are now a
fact of life in the United States. Extensive studies have shown that the
unchecked invasion of non-native species is causing billions of dollars
worth of damage to U.S. agriculture, forestry, and human and wildlife
health, as well as threatening the vital functions that natural
ecosystems support. A less well known fact is that invasive species
threaten one of our most precious natural resources---imperiled species
and communities.

## What Are Imperiled Species?

"Imperiled species" is a general term used to identify species and
populations of animals and plants that are in decline and may be in
danger of extinction. Many imperiled species have legal protection under
Federal laws such as the Endangered Species Act or under State statutes.
Many species, however, are not being protected because of a lack of
knowledge about their status and the environmental factors that may
threaten their future. As the principal research agency for the U.S.
Department of the Interior, the U.S. Geological Survey (USGS) is
conducting research to fill the gaps in our understanding so that
imperiled species can be better managed and conserved.

## How Do Invasive Species Affect Imperiled Species?

Invasive species affect imperiled species and damage natural and human
ecosystems in a number of ways. Examples include the following:

*Predation*. Shortly after World War II, the brown tree snake was
accidentally introduced from its native range in the South Pacific into
Guam, probably as a stowaway in ship cargo. Like many island ecosystems,
Guam is particularly vulnerable to invasive predators because it has few
native predators. With abundant prey and no significant predators to
control them, brown tree snakes multiplied unchecked, reaching densities
of up to 13,000 per square mile. These mildly venomous predators have
virtually wiped out the native forest animals. Ten species of birds,
some found nowhere else, have disappeared from the island. Brown tree
snakes have also caused thousands of power outages by crawling onto
electric lines, killed domestic poultry and pets, and invaded human
habitats. There is the very serious risk that brown tree snakes may be
introduced accidentally onto other Pacific islands as passive stowaways
in ship and air

traffic from Guam. USGS researchers are actively developing methods to
control this threat to native species and providing guidance on how to
reduce the spread of brown tree snakes. To find out more about brown
tree snakes, visit the National Invasive Species Information Center Web
site at http://www.invasivespeciesinfo.gov.

*Altered Ecosystems.* Invasive species can affect entire ecosystems. In
recent years, the Great Basin and High Plains of the Western United
States have been transformed by fire. Fire is a natural component of
these ecosystems, but the frequency and timing of fires have increased
sharply due to the introduction and spread of invasive non-native
grasses. Introduced species such as buffel grass, red brome, and crested
wheatgrass complete their life cycle early in the fire season, but their
dried stalks are persistent and can add to fuel loads for 2 to 3 years
after the seeds have dropped (see
http://www.usgs.gov/invasive_species/plw/grassfire.html). Native plant
species such as sagebrush cannot survive frequent and intensive fires,
and as a result, these keystone species are disappearing from the
landscape. As native habitat declines, so do the populations of
important native animal species, such as sage grouse. Teams of USGS
scientists are conducting studies to track and control invasive plants,
as well as studying sage grouse and other species adversely affected by
invasive species. The scientists are examining how energy development,
grazing, and other human activities can be modified to reduce multiple
impacts on imperiled species. To find out more about the impact of
non-native grasses, visit the USGS GIS database Sage Grouse and
Shrubsteppe Management in the Intermountain West (at
http://sagemap.wr.usgs.gov).

*Competition*. Most invasive species are generalists that live in a
variety of habitats, including habitats disturbed by human activities.
Zebra mussels were first discovered in the Great Lakes in 1988 and have
since spread throughout the Great Lakes and the Mississippi Valley and
into the Northeastern United States. Zebra mussels have had severe
impacts on native mussel species already at risk of extinction due to
the effects of pollution, dams, and other factors. These invaders
compete directly with native species by removing food sources, occupying
otherwise available space, and anchoring themselves by the thousands to
native hosts, making it impossible for the hosts to function. As many as
10,000 zebra mussels have attached to a single native mussel (see
http://cars.er.usgs.gov/Nonindigenous_Species/Zebra_mussel_FAQs/zebra_mussel_faqs.html).
Zebra mussels tolerate a wide range of conditions and reproduce
extremely rapidly; they can alter species composition and water
chemistry of entire systems of lakes and rivers. USGS biologists and
hydrologists have identified pathways and ways to slow their spread into
new habitats; they have also identified locations where imperiled mussel
species can find refuge from zebra mussels and maintain populations.
Finally, they are discovering ways to rear endangered mussels in
hatcheries and reintroduce them into habitats free of zebra mussels. To
find out more about zebra mussels and other aquatic invaders, check out
the USGS Nonindigenous Aquatic Species (NAS) database (at
http://nas.er.usgs.gov).

## Research for the Future

USGS researchers are creating knowledge and tools to prevent or control
the proliferation of invasive species and to reduce their impacts on our
natural heritage. The USGS is working across science disciplines and
with other partners to bring innovative approaches to resource managers,
policymakers, and the public. For example, the USGS is using advanced
technologies to monitor the distribution and abundance of both invasive
species and native species and communities. These technologies are
important tools in focusing resources to preclude, control, or eradicate
invasive species in sensitive native habitats. Sophisticated computer
models are being applied to forecast which native species and
populations may be at greatest risk. These and other research tools are
being applied by Government agencies and private citizens to turn the
tide of invasive species in the United States and to protect the natural
resources vital to our future.

By Rachel C. Muir

Visit the USGS home page at http://www.usgs.gov or contact:

Rachel Muir

E-mail: rachel_muir@usgs.gov

Telephone: 703-648-5114

U.S. Geological Survey

301 National Center

12201 Sunrise Valley Drive

Reston, VA 20192

Sharon Gross

E-mail: sgross@usgs.gov

Telephone: 703-648-4076

U.S. Geological Survey

301 National Center

12201 Sunrise Valley Drive

Reston, VA 20192

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