Part of Lesson Plan: Population Trends -- Jennifer Terpstra

Activity Overview / Details

Review with the students the three factors that affect the growth of populations: birth, death, and movement into/out of the group (immigration/emigration). With the help of the students, list on the board possible causes of each of these three factors. Their examples should not be limited to humans. Encourage them to brainstorm limitations to populations of different wildlife or organisms. Then review the two types of growth, exponential and logistic. Again with the help of the students, list possible reasons why each may occur. When talking about logistic growth, include a discussion about carrying capacity. A brief example I like to share is The Tragedy of the Commons: A couple hundred years ago, English villagers could graze their cattle and sheep on shared pasture land called the commons. Since grazing was free, villagers would graze as many animals possible on the commons. At times, the commons would be severely overgrazed, after all, those who didn't use the free land would sacrifice their profit while others would continue to benefit. The overgrazing would cause the pastures of the commons to deteriorate, and they would lose all productivity. Referred to as the Tragedy of the Commons, one idea the story illustrates is that an environment has a maximum number of individuals it can support. Provided are two pictures, one with few animals grazing on a productive pasture and one that shows overgrazing. Showing these to students will help them visualize what ideal grazing look like compared to overgrazing. At that point, introduce the activity for the day called Population Trends. Read through the activity with the students.