Alien Invasion!

Invasive Species / Grades 9-12 / Life Science




Focus Question

What are invasive species, why are they a problem, and what can be done about them?

Learning Objectives

  1. Students will be able to define, compare, and contrast invasive species, alien species, and native species.
  2. Students will be able to describe at least three problems that may be associated with invasive species.
  3. Students will be able to describe at least three invasive species, explain how they came to be invasive, and discuss what can be done about them.

Links to Overview Essays and Resources Useful for Student Research

http://coastalscience.noaa.gov/stressors/invasivespecies/
http://oceanservice.noaa.gov/topics/coasts/ecoscience/

Materials

Computers (optional) with Internet access; if students do not have access to the Internet, you can download copies of materials cited under “Learning Procedure,” and provide copies of these materials to each student or student group

Audio/Visual Materials

None.

Teaching Time

One or two 45-minute class periods, plus time for student research.

Seating Arrangement

Classroom style or groups of two students.

Maximum Number of Students

45

Key Words

Invasive species
Alien species
Native species
Vector

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Background Information

What is an “invasive species?” - A species in an ecosystem is considered to be invasive when it is not native (alien) to the ecosystem and causes economic and/or environmental harm, or poses a threat to human health. All types of living organisms (plants, animals, bacteria, etc.) can be invasive.

How do invasive species invade in the first place? - Human activities are the most common means through which alien species are introduced into ecosystems. Even when these species survive, they are not considered invasive unless they cause the type of harm described above. But if an ecosystem does not contain species that are able to control the population of an introduced species, the alien species may become invasive as it reproduces and disperses.

Some alien species have been deliberately introduced through expanded global trade, harvesting exotic marine species for the aquarium industry, and use of non-native species in agriculture and pest control. Kudzu was originally imported from the Orient as an ornamental plant and was widely used for erosion control. But in the absence of natural controls, the alien plant became invasive as it spread and overgrew native plants. The Gypsy moth was imported in the late 1860’s from France in an attempt to establish a silk industry in Massachusetts. The moths escaped and are now a major threat to U.S. forests. Other introductions are accidental. Fruit smugglers have inadvertently caused many outbreaks of the Mediterranean Fruit Fly (medfly), one of the world’s most destructive fruit pests. Medfly larvae are able to develop and feed on fruits of many economically important trees and vegetables, including citrus, peach, pear, and apple. Larvae feed on the fruit pulp and eventually reduce the entire fruit to a juicy inedible mess. The zebra mussel is a well-known example of an invasive species introduced in the ballast water of ocean-going ships. Infestations of these mussels can clog water treatment and intake systems, interfering with many industrial activities, docks and boat engines. Wooden shipping containers may contain insects and plant diseases and were probably responsible for introduction of the wood-boring Asian Long-horned Beetle into the United States. Larvae of these beetles bore large tunnels that disrupt the flow of water and food materials within the tree. Eventually the tree literally falls apart and dies.

There is a similar variety of pathways through which invasive species are spread from the site at which they are introduced. Natural pathways include water, wind, and other species. Wind is particularly significant in dispersing many plant diseases. Biological pathways are called vectors. For example, birds that eat the fruit of alien plants may carry the seeds over long distances before expelling the seeds in their feces. Similarly, cattle are vectors that disperse Tropical Soda Apple seeds. The weed spreads rapidly when cattle are sold from an infested region and transported to uninfested areas.

Human beings may be vectors as well. Female Gypsy moths, for example, lay their egg masses on cars, recreational vehicles, and other surfaces. If humans carry an egg mass into an uninfested area, a new infestation is started. Since the moths cannot fly, human activity can greatly increase the rate at which the moths disperse. In fact, it is estimated that the Gypsy moth invades an additional 15,600 square miles each year (three times the area of Connecticut). Boats and boat trailers have played a large part in the rapid spread of Giant Salvina, a water fern from southeastern Brazil that crowds out native water plants, depletes dissolved oxygen in the water, interferes with migrating birds, and clogs water intakes of irrigation system and electrical generators.

So, some new species come to visit; what’s the big deal? - Invasive species can damage native species, change the native community structure, and can create serious economic problems. Invasive species threaten nearly half of the species currently protected under the Endangered Species Act. A single outbreak of medfly may cost millions of dollars to eradicate. Approximately 50,000 exotic species already are known to exist in the U.S., and this number is increasing. The costs of environmental damage, economic losses, and control measures for invasive species average $138 billion per year, more than all other natural disasters combined.

What can be done about invasive species? - Prevention, early detection and eradication are key strategies for dealing with invasive species. If there had been a response when the Gypsy moth escape was first reported, the moth might never have become established.

Port inspectors from the U.S. Department of Agriculture and U.S. Department of the Interior are responsible for detecting illegal importations of fruit, vegetables, animal products, fish and wildlife. Public education is also a vital part of prevention, and there are a variety of things that individuals can do to prevent inadvertent introductions. Homeowners can avoid purchasing invasive landscaping plants, and can replace invasive garden plants with non-invasive alternatives. Aquarium keepers can avoid introducing exotic fish and other aquatic species into local water bodies. Owners of exotic pets should remember that these pets may become invasive if they escape or are released. Boaters should clean boat and trailers thoroughly before transporting them to a different body of water. Hikers should clean their boots to get rid of weed seeds and pathogens which may have become attached.

The National Centers for Coastal Ocean Science of the National Ocean Service is developing a pilot early warning system that is intended to provide a way to detect aquatic invasive species before they become well-established. This project is initially focused on Hawaii’s marine and estuarine coastal areas. An Internet-accessible database of native coastal species will help marina operators, boaters, and other cooperating groups recognize unusual species that they may encounter. These encounters will be reported to resource managers for further investigation.

Eradication may involve:

Mechanical controls include the use of heavy equipment, power and hand tools, draught animals, prescribed fire, explosives, or manual removal. Cultural controls involve educating people and encouraging actions that minimize the spread of invasive species. Biological controls include the use of natural enemies such as insects or pathogens that attack invasive species and limit their growth or reproduction. Another biological control strategy for invasive plants is to encourage succession (the normal process in which dominant plant species change as an ecosystem matures), so that development of native evergreen conifers and/or hardwoods shades plants underneath and suppresses or eliminates shade-intolerant exotic species. Chemical controls include manipulation of water or soil chemistry to favor growth of native species, as well as pesticides and herbicides. The latter chemicals are generally only used as a last resort since they often affect desirable species as well as invasive ones.

The purpose of this activity is to introduce students to typical causes and impacts of invasive species, as well as sources of information on these species and appropriate remedial actions.

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Learning Procedure

  1. Briefly review the broad concept of invasive species. Be sure students understand the conditions under which an organism typically becomes invasive and are able to differentiate between native species (species that are a natural part of an ecosystem), alien species (species that are not native), and invasive species (alien species that are harmful to native species or humans).
  2. Briefly explain the purpose and activities of the U. S. Coral Reef Task Force (CRTF) and the NOAA Coral Reef Conservation Program (CRCP), and highlight the monitoring functions that are intended to identify reef areas threatened by thermal stress or algal blooms (visit http://www.coralreef.gov for more information on the CRTF and http://coralreef.noaa.gov for more information on the CRCP).

  3. Tell students that they are to prepare a written case study on an invasive aquatic species. Their reports should include the native location of the species, how it was introduced to an ecosystem, where it became invasive, what impacts are associated with the invasive species, and what control measures are possible. Assign one of the following species to each student or student group:
  4. Protista

    Whirling Disease (Myxobolus cerebralis)

    Algae

    Mediterranean Clone of Caulerpa (Caulerpa taxifolia)

    Seed Plants

    Brazilian Waterweed (Egeria densa)
    Common Reed (Phragmites australis)
    Eurasian Water-milfoil (Myriophyllum spicatum)
    Giant Hogweed (Heracleum mantegazzianum)
    Giant Reed (Arundo donax)
    Giant Salvinia (Salvinia molesta)
    Hydrilla (Hydrilla verticillata)
    Melaleuca (Melaleuca quinquenervia)
    Purple Loosestrife (Lythrum salicaria)
    Water Chestnut (Trapa natans)
    Water Hyacinth (Eichhornia crassipes)

    Invertebrates

    European Green Crab (Carcinus maenas)
    Zebra Mussel (Dreissena polymorpha)

    Fish

    Alewife (Alosa pseudoharengus)
    Asian Swamp Eel (Monopterus albus)
    Eurasian Ruffe (Gymnocephalus cernuus)
    Lionfish (Pterois volitans)
    Northern Snakehead (Channa argus)
    Sea Lamprey (Petromyzon marinus)

    Amphibians

    North American Bullfrog (Rana catesbeiana)

    Mammals

    Nutria (Myocastor coypus)

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  5. Have students present their research results orally, and lead a discussion to summarize means of introduction, typical environmental, economic, and/or social impacts, and potential control measures. The following points should be included in these presentations:

Whirling Disease (Myxobolus cerebralis)

The Mediterranean Clone of Caulerpa (Caulerpa taxifolia)

Brazilian Waterweed (Egeria densa)

Common Reed (Phragmites australis)

Eurasian Water-milfoil (Myriophyllum spicatum)

Giant Hogweed (Heracleum mantegazzianum)

The Giant Reed (Arundo donax)

Giant Salvinia (Salvinia molesta)

Hydrilla (Hydrilla verticillata)

Melaleuca (Melaleuca quinquenervia)

Purple Loosestrife (Lythrum salicaria)

Water Chestnut (Trapa natans)

Water Hyacinth (Eichhornia crassipes)

European Green Crab (Carcinus maenas)

Zebra Mussels (Dreissena polymorpha)

Alewife (Alosa pseudoharengus)

Asian Swamp Eel (Monopterus albus)

The Eurasian Ruffe (Gymnocephalus cernuus)

Lionfish (Pterois volitans)

Northern Snakehead (Channa argus)

Sea Lampreys (Petromyzon marinus)

North American Bullfrog (Rana catesbeiana)

Nutria (Myocastor coypus)

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The Bridge Connection

The Bridge is a growing collection online marine education resources. It provides educators with a convenient source of useful information on global, national, and regional marine science topics. Educators and scientists review sites selected for the Bridge to insure that they are accurate and current.

http://www.vims.edu/bridge/ - On the navigation menu to the left, click “Ocean Science Topics,” then “Biology,” then “Exotics” for links to sites and activities dealing with invasive species.

The “Me” Connection

Although invasive species can cause serious problems for humans and other species, they are only doing what every other organism does: taking advantage of opportunities to survive and perpetuate their species. Have students write a brief essay, describing how the human species might be considered invasive by one or more other species, and what those species might do to deal with these “invaders.”

Extensions

Visit http://www.invasivespecies.org/resources/TimeWarp.html for an activity that uses invasive species control and eradication techniques to increase participants’ abilities to use a group planning and decision-making process, and to compromise within a small group.

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Resources

http://coastalscience.noaa.gov/stressors/invasivespecies/ – Background information on invasive species from the National Centers for Coastal Ocean Science, National Ocean Service

http://coastalscience.noaa.gov/documents/factsheet_invasivespecies.pdf – Aquatic Invasive Species: Early Detection, Warning, and Information Factsheet

http://invasivespecies.nbii.gov – The Invasive Species Information Node (ISIN) of the National Biological Information Infrastructure with information on identification, description, management, and control of invasive species; hosted by the Department of the Interior, U.S. Geological Survey

http://www.invasivespecies.gov – A gateway to federal efforts concerning invasive species, including links to species profiles, geographic information, news and events, laws and regulations, resources, management tools, databases, and information on vectors and pathways

http://www.invasivespeciesinfo.gov/ – National Invasive Species Information Center from the U.S. Dept. of Agriculture, with Information profiles for many invasive species

http://www.invasivespecies.org/resources/ – website for Invasive Species Educational Resources

http://nature.org/initiatives/invasivespecies/ – Web page for the Nature Conservancy’s Invasive Species Initiative

National Science Education Standards

Content Standard C: Life Science

Content Standard F: Science in Personal and Social Perspectives

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Ocean Literacy Essential Principles and Fundamental Concepts

Essential Principle 5. The ocean supports a great diversity of life and ecosystems.

Essential Principle 6. The ocean and humans are inextricably interconnected

Essential Principle 7. The ocean is largely unexplored.

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