Grasshopper population dynamics, part II: Visualizing and understanding data

Author: Gordon Bennett

Overview: In this lesson, part II of a series, students will review the life cycle of grasshoppers, learn how to identify grasshopper species using a dichotomous key and observations of insect morphology, convert their fall observations of grasshopper populations (numbers of males, females, nymphs and adults) into numerical data, and construct graphs to visualize and interpret the data. Based on the fall data and their knowledge of the life cycle, they will discuss hypotheses about what the population might look like in the spring.

Lesson Goals:

  • Review the life cycle of grasshoppers

  • Learn to use morphology and a dichotomous key to classify/identify grasshoppers

  • Convert observations from the fall grasshopper collections into a quantitative data set

  • Practice using graphs to visualize and interpret data

  • Pose and address a research question: What happens to grasshopper populations between the fall and spring?

  • Use knowledge of grasshopper life cycles and the fall grasshopper population data to develop ideas (hypotheses and predictions) about what the structure of the population might be in the spring

  • Prepare for spring collecting and analysis of Sagehen Creek Field Station's meadow grasshopper populations

Standards:

  • Statistics, Data Analysis, & Probability Standard 1.2: Organize and display single-variable data in appropriate graphs and representations and explain which types of graphs are appropriate for various data sets.

  • Investigation & Experimentation Standard 6a: Classify objects in accordance with appropriate criteria.

  • Investigation & Experimentation Standard 6b: Develop a testable question.

  • Investigation & Experimentation Standard 6g: Record data by using appropriate graphic representations and make inferences based on those data.

  • Investigation & Experimentation Standard 6h: Draw conclusions from scientific evidence and indicate whether further information is needed to support a specific conclusion.

Grade span: 5

Lesson summary: In the fall, students initiated a three-part research project to investigate changes in grasshopper populations over the course of a year. This lesson will be important in giving students the mathematical tools and skills for completing the grasshopper population project in the spring.

This classroom lesson has two parts. The first part reintroduces the field research project begun at Sagehen Creek Field Station in the fall, and its subject: grasshoppers. Students will closely observe and identify real grasshopper specimens from a museum collection using a scientific (dichotomous) identification key to compare and consider differences between grasshopper species. The key created for their use will highlight some of the basic insect morphology that was discussed in the fall. This will engage students in the initial steps in understanding how scientists classify and understand biodiversity. In the second part of this lesson, students develop a data set from their fall observations, graph it and discuss testable questions about the grasshopper population at Sagehen.

Teaching tips: Have fun, help the students own the investigation. Be very clear, precise, and repetitive about the vocabulary and concepts, provide visuals for new vocab and concepts. There are a lot of terms and concepts that may be foreign to some students. Ask lots of clarifying questions to make sure students understand these concepts, and know why we are doing this.

Vocabulary: biodiversity [grasshopper], population, demographics, dichotomous key, data, bar graph, error, head, thorax, abdomen, legs, wings, antenna, life cycle, dormant, egg, adult, nymph, female, male

Materials/preparation:

  • Pinned grasshopper specimens* in foam collecting trays, ~1-2 specimens per box, approximately 20 displays, one per student (*four species: Clearwinged Grasshopper (Camnula pellucida), Plains Lubber Grasshopper (Brachystola magna), Meadow Grasshopper (Chorthippus curtipennis), Spotted grasshopper (Cordillacris occipitalis); Sagehen grasshopper biodiversity is dominated by Camnula pellucida and Chorthippus curtipenni)
  • Magnifiers
  • Simplified grasshopper species key
  • Optional grasshopper information handouts for Camnula and Chortippus
  • Poster paper and markers
  • Poster of example [dichotomous] key — characteristics and specimens will be of students or fellows (e.g., head has hair, eyes are blue, etc. — simple superficial characteristics)
  • Poster of grasshopper life cycle and body parts
  • Graph paper with labeled axes

Time: 60 minutes

Procedures/instructions:

Opening: 30 minutes — Introduction and classification activity

  1. Introductions (~5-10 min)
    1. Introduce yourself again, and try to have the students remember two things about you as a scientist
    2. What is an entomologist? What kind of science or research did we do in the fall?
    3. What is the organism we are studying? What is the question(s) we are trying to answer?
    4. Put the major question — the focus — of this project on the board (What happens to grasshopper populations between the fall and spring?)
  2. Science of Biodiversity! (~20 min)
    1. Identifying insects
      1. Split Students into groups of 2-3 (this can also be done individually or in larger groups). If students need to move chairs or places, arrange this first before starting activity.
      2. Introduce a [dichotomous] key. Fellows model how to use the key to tell apart four student volunteers. Use poster paper to write out a model key.
      3. Put up a poster of the grasshopper life cycle to remind students how to distinguish nymph v. adult, and female v. male. This should be review.
      4. Pass out a pinned grasshopper (museum specimens), a magnifier, and simplified key (see PDF) to each group.
      5. Have students observe closely and determine which species they have (this should take 5-10 min).
    2. Discussion — allow at least five minutes for discussion
      1. Discuss process of identifying grasshoppers:
        — Two of the four grasshoppers aren't found at Sagehen, which ones? (answer: Plains lubber and Spotted-wing grasshoppers)
        — What are some ways we can tell grasshoppers (species) apart?
        — What are some specific characteristics of different species
      2. Why is it important that we know the biodiversity of grasshopper species?
      3. Is a dichotomous key useful?
      4. Bring students back to their desks if they have moved.

    Main Lesson: 30 minutes — Population demographics: Visualizing and understanding the data

    1. Review
      1. Our purpose: Project on grasshopper population demographics
      2. Refer to our research question: What happens to grasshopper populations between the fall and spring?
      3. Write population demographics on the board: Ask students what this means; write out the meaning on the board. [A population is a group of individuals of the same species living and interbreeding within a given area. Demographics is information about the characteristics of populations, such as number of individuals, number of males and females, adults, juveniles, how it changes over time, mortality rates, etc.]
      4. Ask the students: What did we observe in the fall? What do you remember? Did we record data? What for? Adults/nymphs? etc.
      5. Have students think about the hypotheses they might make with respect to the grasshopper population changes between the fall and spring.
      6. Place a generalized hypothesis for the class on the board (e.g., "There will be more nymphs in the spring because …," etc).
    2. Data
      1. Pass out their data sheets and have students review what they found.
      2. Ask them what data is. What kind of data did we collect? Help students remember the types of data we recorded: adults vs. nymphs, and males vs. females.
      3. If the data sheets cannot be found, have a set of pre-fabricated ones that resemble the general results of other classes. See templates from the fall.
      4. Create a combined class data set by having students go up to the board and place a mark in the category that matches their specimen/record (e.g., adult male, female nymph, etc.) — demonstrate this process. Students can put several marks if they have more than one record.
      5. Discuss
        — What appears to be the most, least?
        — What patterns do you see?
        — Is there a better way for us to view this, to make more sense?
    3. Bar graph
      1. Intro: Why do we use graphs? What is the purpose?
      2. Pass out graph template, and have students tally each category.
      3. Model how to fill in bar graph; include previous years 2003, 2008 to model graphing
      4. Have students complete their graphs. Teachers should complete a graph of their data too.
      5. Examine the graph with students. Ask:
        1. What do we see?
        2. What can we tell about grasshoppers in the fall?
        3. Does this fit our hypothesis? (refer back to one made by students at beginning of class)
        4. What do we think we will see in the spring? What would that graph look like?

    Discussion/wrap-up/what did we learn: To finish graphing activity, ask students about their sampling.

    • Does it tell the whole story?
    • Is it possible we missed something or didn't sample enough?
    • Are there errors? What might they be?
    • Can we trust our data?

    Extensions (optional): Spring sampling/collection of grasshoppers at Sagehen will allow testing of ideas about seasonal changes in grasshopper populations.

 
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