• Collect and check the Predator-Prey Interaction handout.

• Assess whether students understand predator-prey interactions by discussing the analysis and conclusions to the simulation.

• Orally assess whether students understand the categories of limiting factors during the whole-class graphic organizer activity.

• Circulate around the room and discuss students’ investigation procedures, asking them to describe the limiting factor(s) in their experiments.

• Collect students’ graphs from the Predator-Prey Interactions activity.

Preparation: Cut index cards into large and small squares (see Materials list and S-B-2-2_ Predator-Prey Cards.docx); place them into baggies for each group.

Part 1: Predator-Prey Simulation

Begin by asking students to define predator and prey and give examples of predator-prey relationships from the food chains and food webs in Lesson 1. These concepts should be prior knowledge.

Small-Group Activity: Predator-Prey Interactions

Divide students into groups of three to four students and distribute the predator and prey cards (S-B-2-2_ Predator-Prey Cards.docx) and the Predator-Prey Interactions handout to each group (S-B-2-2_ Predator-Prey Interactions.docx). Read through the procedure with students and answer any questions they have. Have student groups complete the activity, recording their data in the Predator-Prey Data Table (S-B-2-2_ Predator-Prey Interactions.docx). Have students answer the analysis questions and write their conclusions, and then discuss their conclusions about the relationship between the sizes of predator and prey populations.

Explain exponential growth in populations. Then, explain logistic growth and carrying capacity using the double-line graph students created. Reserve discussion of limiting factors for Part 2.

Part 2: Limiting Factors

Ask students to consider the Predator-Prey Simulation. Ask, “What stops the mouse population from growing bigger and bigger?” and “What stops the fox population from growing continuously?” Explain that predator-prey relationships are an example of a limiting factor, because they control the population size of both the predators and the prey.

On the board, write “Population Size” in a circle. Draw several circles near the first circle, and write “Predation” in one of them. Guide students in determining other limiting factors for populations. Limiting factors include (but are not limited to): competition, parasitism, disease, natural disasters, drought, forest fires, and human disturbances. Have students copy the graphic organizer into their notes, and allow time for them to write down any examples they can think of for the limiting factors (e.g., weeds and crop plants competing for light, space, and nutrients in a vegetable garden). Have students share their ideas.

Explain the difference between density-dependent and density-independent limiting factors. Have students label each of the limiting factors in their notes into one of these categories (“D.D.” and “D.I.”). Density-dependent limiting factors include competition, predation, parasitism, diseases and density-independent limiting factors include drought, natural disasters including forest fires, and human disturbances such as clear-cutting forests and hunting.

Partner Activity: Designing an Experiment on Limiting Factors

Have students design an investigation on how plant competition affects seedling growth. Have pairs of students begin by writing a hypothesis (e.g., “If seedlings have more space, they will grow faster than seedlings with less space.) Check hypotheses before students proceed with developing the investigation. Then, students write a materials list and step-by-step procedure to test the hypothesis. If possible, allow students to conduct the investigation over about two weeks to test the hypothesis. Discuss how limiting factors can affect plant growth.

Extension:

• For Part 1, assist students who may need opportunities for additional learning by modeling the first several steps of the Predator-Prey Simulation procedure and showing students how to record their data.

• Challenge students performing above and beyond the standards by having them create a double-line graph of their data. Alternatively, have them create an alternate version of the simulation that includes wolves as fox predators.

• Another extension for predator-prey interactions is having students complete the online activity Leopard Seals and Penguins: A Delicate Balance (see the Leopard Seals and Penguins: A Delicate Balance Web site in Related Resources).

• For Part 2, assist students who may need opportunities for additional learning by guiding them in making a table on the limiting factors discussed in this lesson with the headings “Factor,” “Definition,” and “Example.”

• Challenge students performing above and beyond the standards by having them research the limiting factors on the gray wolf population in the United States and the efforts that have been made by humans to reintroduce the gray wolf. Then have them write a persuasive essay for or against reintroducing gray wolves. (See Related Resources for more information.)