- Understand the distinction between native and alien, naturalized and invasive species.
- Identify a variety of native and non-native species that live in their area.
- Recognize the fundamental characteristics of invasive species.
- Research and prepare for a debate in which they assume an affirmative or negative position on an invasive species issue.
- Argue a case logically by using facts and evidence to refute or back up claims.
- Work effectively as a team.
Students compare and classify native and alien species, then research and hold a classroom debate about the differences between indigenous and exotic species, their positive and negative effects, and whether their populations should be conserved or controlled.
images of native and alien species that inhabit your area; access to library and Internet resources, magazine articles, newspaper clippings, documentaries, and other media concerning the alien invasion; student handout on debating guidelines
The growing invasion of our lands and waters by alien species is an ecological emergency, second only to habitat destruction in endangering native animals and plants. Yet, biologists cannot always agree on what is or isn't an alien species, whether or not it is invasive, and whether action should be taken to control or eradicate its unwanted population.
Most experts do agree, however, that alien species are animals and plants that have been intentionally or accidentally introduced into an environment outside their native geographic range. They're uninvited guests, like the green crab, red-eared slider, and spiny water flea, not to mention such homegrown trespassers as bullfrogs from the East overrunning the West and rainbow trout from the mainland encroaching on Newfoundland.
Native species, on the other hand, naturally occur in the ecosystem where they live. They have evolved over millions of years in association with other animals and plants in a delicately balanced food web.
In fact, many thousands of alien species now inhabit our home and native land. Some of them, like the ring-necked pheasant, honeybee, and brown trout from Eurasia, actually boost the web of life and are usually regarded as "naturalized" species. Others, such as the European starling, zebra mussel, and purple loosestrife, cause huge ecological and economic harm and are considered not only alien but also invasive. Still others, like the Asian carp and northern snakehead (both imported from China to the United States), are in position to enter our waters from south of the border, with potentially catastrophic consequences.
The flow by no means goes only one way. Raccoons imported from North America have become a masked menace in Europe and Asia. Grey squirrels are an agricultural pest and have nearly driven the red squirrel into extinction in Europe. And beavers introduced from Canada are overrunning Tierra del Fuego at Argentina's southernmost tip.
- Discuss with the class key points in the "background" section (above) and define such vocabulary items as native, non-native, alien, exotic, naturalized, and invasive.
- From a box, select photos or illustrations of native an alien species found in your area. Examples of native species might include the wood rat, grizzly bear, lake trout, painted turtle, and eastern bluebird. Examples of alien species might include the sea lamprey, house sparrow, wild boar, domestic cat, and Norway maple. Students should be familiar with some of the species, based on "Aliens among Us" and the "Field Guide to Invasive Species". Have the class identify each plant or animal and vote if it is "native" or "alien." Were there any surprises, such as species thought to be indigenous that turned out to be introduced.
- Now, discuss the similarities and differences between native and alien species. Ask students for suggestions on how to classify or tell them apart. Have them brainstorm the characteristics of natives versus aliens. For example, conservation biologists have observed that, compared to indigenous species, most exotic animals and plants are much less likely to survive in Canada. Often, however, exotic species that are well adapted to their new environment:
- reproduce much faster;
- have fewer predators;
- are more competitive; and
- do more harm than good in their adopted habitats.
- Divide the class into teams of five students. Each team will choose one of three debate statements, taking either an affirmative or a negative stance. Here are some examples:
- "The distinction between native (indigenous) and alien (exotic) species is obvious. Our environment abounds with clear examples of these living opposites. There is no good reason to be confused about the difference."
- "Even though a species is alien, it is wrong to say whether it is invasive or non-invasive, harmful or helpful. For example, some introduced species are beneficial and judged to be "naturalized," while some native species are considered invasive and have more negative than positive effects. There is only one species that is truly invasive - and it's called Homo sapiens."
- "The alien invasion is causing massive environmental destruction all throughout Canada and the world and costing the economy billions of dollars every year. We cannot sit back and let nature take its course. No cost or effort should be spared to get this ecological crisis under control."
- The debate is about a statement relating to the alien invasion.
- It has two sides: affirmative and negative. The team that supports the statement is called the affirmative position. The team that opposes the statement is called the negative position.
- Apart from the students who conduct the debate, each member of the class belongs to a team. Everyone on your team has one or more of the following roles: lead debater, questioner, answerer, rebutter, and closer.
- The students assigned to administer the debate take the roles of moderator, timekeeper, and scorers.
- Your entire team will be scored as a whole, so be sure that all members work together and have ample background on the issues and the positions you will take.
- No interruptions from opposing positions are permitted during the debate.
- All team members should pay close attention to affirmative and negative arguments..
- Only one team will win, based upon the scorers' evaluation of each member's performance during the debate.
- The moderator announces the statement to be debated and introduces each speaker sequentially after the timekeeper calls time.
- The timekeeper keeps careful track of the time, letting participants know when they have one minute left to speak and when their time is up.
- The lead debater for the affirmative position presents opening arguments supporting the statement. Members of the negative position listen carefully and modify their questions, which will be used to cross-examine the affirmative position. (three to five minutes)
- The questioner for the negative position cross-examines the answerer for the affirmative position concerning the opening arguments. All questions should be clear, concise, and prepared in advance. The affirmative answerer should also be well prepared to respond. (three minutes)
- The lead debater for the negative position presents opening arguments opposing the statement. Members of the affirmative position listen carefully and modify their questions, which will be used to cross-examine the negative position. (three to five minutes).
- The questioner for the affirmative position cross-examines the answerer for the negative position concerning the opening arguments. All questions should be clear, concise, and prepared in advance. The negative answerer should also be well prepared to respond. (three minutes)
- The affirmative rebutter counters arguments in the negative answerer's response. (three minutes)
- The negative rebutter counters arguments in the affirmative answerer's response. (three minutes)
- The affirmative closer refers to new issues raised during the debate, sums up the position supporting the statement, and presents closing arguments. (three to five minutes)
- The negative closer refers to new issues raised during the debate, sums up the position opposing the statement, and presents closing arguments. (three to five minutes)
- The scorers evaluate each team's performance in the opening arguments, cross-examination, and closing arguments in response to a rubric.
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