Who's Who?

Overview: This exercise will create an awareness of the ways we may identify exotic species.

Audience: This activity is designed for upper elementary and middle school students in grades 5-8.

Background: To identify species that have the potential for negative ecological impacts, we need to be able to recognize exotic species. Distinguishing exotic organisms from similar-looking native organisms often requires identification and classification skills such as those practiced here. Organisms may be identified by comparing and contrasting their physical features. A dichotomous key, in which one chooses which of two statements (forming a "couplet") best describes the unknown organism, is a very helpful tool for identification. In this lesson, prickly plants are used as examples of organisms that can look very similar but have very different impacts. Land managers, extension personnel, and county weed supervisors need to be able to distinguish native thistles from the exotic species that are noxious weeds and must be controlled. [The ESCAPE web site (http://www.unk.edu/escape) provides additional information on exotic species, an overview of basic ecological concepts, a key to thistles of Nebraska, and a glossary.]

Time Requirements: This activity can be completed in a 45-minute period.

Objectives: After completing this exercise, students will be able to:
1. List some characteristics that are used in species identification.
2. Use a dichotomous key to identify organisms based on their characteristics.

National Science Education Standards:

• Unifying Concepts and Processes
  • Systems, order, and organization
  • Form and function
• Science as Inquiry
  • Abilities necessary to do scientific inquiry
• Life Science
  • Interdependence of organisms
• Science in Personal and Social Perspectives
  • Natural resources
  • Environmental quality

Materials:

• Computers with access to the Internet
  
• [Optional] A weedy area in which prickly plants may be observed
• [Optional] Fresh or pressed specimens of thistles

Anticipatory Set:
Present students with this scenario: Mr. Hernandez is a rancher. He has found a small patch of prickly plants in one of the fields where his cattle graze. He is concerned that the plants may be musk thistle, a troublesome weed that crowds out the plants that his cattle feed on. He is worried that if he does not take some action, this weed could spread. However, Mr. Hernandez knows that all prickly plants are not problem plants, and some are a natural part of the grassland vegetation. How can he determine whether he should spray this patch of plants or leave it alone?

Procedure:
1. Present the above scenario. Tell students that not all plants with thorns are thistles, and not all thistles are weeds. Ask, "What information does Mr. Hernandez need in order to determine if this plant is a problem weed?" Write student responses on the blackboard. Brainstorm a list of resources that might be used to find this information.

2. If students have not already realized that Mr. Hernandez needs to identify the plants in his field, suggest that identification of the species is the first step in knowing whether this plant might be a problem. Tell students that a useful tool for identifying an unknown species is a dichotomous key, and that they will be learning how to build and use one. Tell students that "dichotomous" means there are two choices, and that by choosing which of the two choices best describes the organism, one works through the "key" to find the name of the organism. Tell them that what they will do next is come up with a key to identifying the name of a student in the room based on his or her characteristics.

3. To illustrate how a dichotomous key works, have all the students stand up. Tell the students that they must decide how to divide themselves into two groups. The groups do not have to be of equal sizes but all the members of each group must have something in common. If students have difficulty determining the criterion for grouping themselves, suggest that all the girls form one group and all the boys form another. Ask students, "What characteristic did you use to decide which group you belonged in?" Tell the students that this characteristic can be used to form the first step in our classroom key.

4. Write the first couplet on the board. If the students have used gender as the first grouping character, write "1a. Male ... go to 2." Directly below that statement, write "1b. Female ... go to ___." (Leave this number blank until the males have been identified.) Now tell the students that they must determine what characteristic will be used in the second step to separate the males into two groups. Allow the girls to make suggestions, as well as the boys. Possible characteristics include glasses vs. no glasses, right- vs. left-handed, wearing jeans vs. not wearing jeans, and so on. If students suggest a characteristic such as hair color, point out that some people have hair that is neither blond nor brown, but somewhere in between. Encourage them to make the distinctions between the two groups clear so that the choices are easy to make. Non-physical characteristics might be used (such as "likes pizza vs. doesn't like pizza") but be sure to point out that usually only physical characters are used in keys for organisms.

5. When there is only one student that has fits the description for a couplet statement, write that student's name at the end of the statement. For example, if only Tina is wearing a dress, then the couplet might read "6a. Wearing a dress ... Tina. 6b. Not wearing a dress ... go to 7." Continue writing couplets until students understand how to build the key, but stop while there are still several groups that have not been fully identified. Challenge each group to continue the process to complete the key. A template may be used to assist with formatting the couplets. To avoid confusion in numbering, students may draw arrows to show how couplets are connected.

6. When each group has completed writing all the couplets necessary to identify their members, have them report their work. Fill in the couplet numbers to complete the key. Check its accuracy by "keying out" a few students (that is, starting from the first couplet and stepping through the choices to arrive at the correct name). For fun, invite a staff member, such as the school principal, to use the classroom key to identify a few students. This will reinforce the idea that a key written by one person can be used by others. This is how people with little knowledge of how to tell one species from another can use a key developed by an expert.

7. Relate this back to the notion of identifying the plants in Mr. Hernandez's field by asking students to think of the characteristics that might be used to build a key for prickly plants. Ask, "How can we tell one prickly plant from another?" List their responses on the board.

8. Have the students find out how their list compares with the characteristics used to identify thistles in the Thistle Identification section of the ESCAPE web site. As students browse through the thistle key, they should note the structural features (leaf shape, flower color, etc.) of the plants that are used to distinguish between species. As an extra challenge, students can try to figure out what characteristics would indicate that the plants in Mr. Hernandez's pasture are, indeed, musk thistles.

Extension: Take students to an area where different kinds of weedy plants may be found. Tell students to walk through the area and find a prickly plant. Remind them to be safe about touching the plants. Allow them to make careful observations of the plants, recording as many characteristics as possible. Challenge students to use the dichotomous thistle key and "look-alikes" pages on the ESCAPE web site to identify the plants they observed. Variation 1: Have students trade descriptions and try to identify the prickly plants from the recorded observations. Variation 2: Provide students with thistle specimens, either fresh or pressed, and allow them to work through the thistle key to determine whether the plants are native or exotic.