TEACH!: Unit 3, Lesson 2.

We’re all connected: Ecology and the circle of life:

Alien Attack:
Invasive Species


The learner will understand the nature and impact of invasive species in general, and will be introduced to a few specific examples
of local invasive species.


  • Images of a variety of species (some native/some non-native)
  • Packets of species-specific info on a variety of invasive species.


Ecosystem components all have a job to do and each one helps to keep the whole in balance. Sometimes, non-native, or “alien”, species arrive in an ecosystem and throw the system out of whack. Though some aliens fare poorly outside their traditional environment, those that survive and thrive often cause problems and are called “invasive species.” The introduction of these non-native species to an ecosystem harms, or is likely to cause harm, to the economy, environment or human health. Invasive species cause one of the most serious global environmental challenges we face today. Left unchecked, they can transform entire ecosystems by out competing or consuming native species to the point of no return. By crowding out native species, they reduce global biodiversity.

The manner in which an invasive species enters or spreads throughout a non-native ecosystem is called a pathway or vector. Pathways can be natural or a result of human activities. Species can travel via weather patterns, tides and water currents, or within the digestive tract of a migratory animal. New species are imported for use in aquaculture, aquaria, and gardening. Other human pathways include shipping materials, ballast water, trucks and recreational boats, and even the shoes of travelers.

“Alien species” means, with respect to a particular ecosystem, any species, including its seeds, eggs, spores, or other biological material capable of propagating that species, that is not native to that ecosystem.

“Invasive species” means an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.

“Native species” means, with respect to a particular ecosystem, a species that, other than as a result of an introduction, historically occurred or currently occurs in that ecosystem.

(Executive Order 13112, Federal Register February 8, 1999, Volume 64, Number 25)

Alien species become invasive when they are more successful at surviving in an ecosystem than native species. There are four general qualities that characterize invasive species. The more qualities a species possesses, the more widespread and trouble some the species becomes.

  • Productivity: reproduce quickly, produce many offspring or huge volumes of seeds.
  • Dispersal: individuals or seeds and other reproductive parts spread very easily,  adapting easily to new areas.
  • Growth period or seasonal advantages: tolerates growing or living conditions that native species can’t. For example, they may leaf out early and stay green longer than native plants.
  • Lack of natural controls: absence of natural predators, pests, diseases or other limiting factors.

Invasive species control and damage mitigation measures cost billions of dollars annually. Several laws prohibit the introduction of alien species in the United States, but accomplishing this requires cooperation among multiple federal and state agencies, the support of trade organizations, public education and a lot of luck.

In preparation for this lesson, the instructor should gather packets of materials about several invasive species. Establish packets on species common to your area from a variety of sources. You might include flyers, posters, brochures, copies of web pages, etc. Suggested sources for Pennsylvania species include the Pennsylvania DCNR, Pennsylvania Sea Grant, the Penn State University Cooperative Extension, Pennsylvania Department of Agriculture, the Governor’s Invasive Species Council of Pennsylvania, and the US Fish and Wildlife Service. There are plenty of others. We recommend one packet on each of the following species, feel free to add more:

  • Terrestrial plants:
    • Tree-of-heaven (Alianthus altissima)
    • Mile-a-minute weed
  • Aquatic plants:
    • Curly leaf pondweed
    • Eurasian watermilfoil


1. Introduce the activity by showing a series of images (PowerPoint, posters, etc.) of a variety of species. Ask participants to guess whether that species is native to the area or not. Explain what a “native” species is.

2.  Discuss the distinction between alien and invasive species. Not all alien species become invasive!

3. Provide a short explanation of the qualities of invasive species. Provide examples.

4. Divide participants into small groups. Distribute one packet of information to each group. This will be their species to learn about and present to the rest of the group.

5. Instruct groups to explore the materials and develop a one to two minute presentation for the rest of the group on their species. They should plan to mention where the species came from, how it traveled to the area, where/how it lives, what qualities make it invasive, how it influences native species, and what work is being done to control it.

6. After the participant presentations, wrap up the lesson with the following discussion points:

  • What makes a species invasive?
  • Why should invasive species be controlled or prevented?
  • What happens when invasive species are not controlled?
  • Discuss specific examples of invasive species control measures

Note to the presenter: Be sure to wrap up this lesson with a positive discussion of what’s being done to prevent and mitigate invasive species. Check the Pennsylvania Department of Conservation and Natural Resources web page to learn about successful projects underway. Participants should leave knowing how they can help and feeling optimistic about their power to improve the situation, not depressed about a gloomy future!


Pennsylvania Department of Conservation and Natural Resources

Pennsylvania Sea Grant

This site will give you a comprehensive introduction to the aquatic invaders in Pennsylvania.

Governor’s Invasive Species Council of Pennsylvania

This site provides profiles of Pennsylvania invasives in addition to information on the current management plans in the state.

USDA National Invasive Species Information Center

Union of Concerned Scientists

Article title: Will climate change hasten the spread of invasive species?

Continue to:
Unit 4, Lesson 1.:  What little brown bird is that? Basic birding.

Go Back to:
Unit 3, Lesson 1: How does it fit together? Diagramming an ecosystem

Updated: May 2018