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

Imperiled Species and Communities 

Threatened by Invasive Species

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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 (fig. 1) 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 (fig. 2), and as a 

result, these keystone species 

are disappearing from the 

landscape. As native 

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005–3110

March 2006

Figure 1. Brown tree snake. The “cat 

eyes” appearance is a distinguishing 

characteristic. Photographs by Gordon 

Rodda, U.S. Geological Survey; from 

http://www.forestryimages.org.
About LINKS Fact Sheets. The mission of the U.S. Geological Survey is to provide 

quality science information in the disciplines of biology, geology, geography, and 

hydrology. Its diverse array of experience and expertise enables the USGS to 

conduct interdisciplinary science in support of its mission goals. LINKS 

Fact Sheets present information on how USGS programs 

work together to address the complex science 

needs of the Nation.

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 (fig. 

3), making it impossible for the hosts 

to function. As many as 10,000 

zebra mussels have 

Figure 2. Unlike native sagegrass, 

invasive non-native grasses can 

withstand frequent and intense wildfires. 

Photograph courtesy of the U.S. 

Geological Survey.

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

Figure 3. Zebra mussels anchor themselves by 

the thousands to native bivalve hosts. Photograph 

by Randy Westbrooks, U.S. Geological Survey; from 

http://www.forestryimages.org.

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

Rachel Muir Sharon Gross

E-mail: rachel_muir@usgs.gov E-mail: sgross@usgs.gov

Telephone: 703-648-5114 Telephone: 703-648-4076

U.S. Geological Survey

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