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Night Creatures of the Kalahari

Classroom Activity

Objective
To explore the balance between predator and prey.

• copy of "Life in a Bottle" student handouts
  Life in a Bottle (PDF or HTML)
  Food Chain Chambers (PDF or HTML)

1. An ecosystem such as the Kalahari has a system of checks and balances to ensure that no species overpopulates and threatens the survival of other species. Students can explore the balance between predator and prey in this activity.

2. Begin by establishing a set of Food Chain Chambers. Insert the predators (spiders) and the fruit that will attract the prey (fruit flies), according to the instructions for each chamber. Students might need to trap their initial fruit fly population at home in a kitchen or near a compost pile. They can then bring the chambers to the classroom for observation.

3. Copy and distribute the "Life in a Bottle" student handout. Over the next three to five weeks, students will record observations and make predictions for each chamber (one control chamber and three chambers in which variables have been altered). After the final observations, ask students to give examples of real-life instances modeled in these chambers.

4. Conclude the activity by having students think of ideas for additional ways to test predator-prey relationships.

Teachers: How You Can Find Spiders
You can either look for small, non-poisonous, web-building spiders in basements, garages, windows, corners of rooms, under boards or rocks, or on or under porches, or you can order spiders from school science suppliers (you can also order fruit flies). Place each spider in a paper cup and secure with plastic wrap (do not leave the spider in the cup for more than an hour). Although most spiders prefer not to bite people, never handle the spider with bare hands. In particular avoid two families of spiders—the female black widow spider and the brown recluse or the violin spider, shown below.

In Control Chamber 1, fruit flies will lay eggs on the fruit, and the number of individuals in their population will increase. The spider will control the fruit fly population by eating any fruit flies that make it through the trap. In this chamber, a healthy balance between the population of fruit flies and the spider will exist until the fruit is consumed. In the "no fruit" Chamber 2, fruit flies will not inhabit the chamber, and in the "no fly" Chamber 3, the fruit will become moldy. In each of these chambers the spider will eventually starve to death if it is not fed or released. Students will quickly be able to predict this outcome. In the interest of the spider, either feed it a small insect such as an ant or small cricket or release it within 10 days. In the "no spider" Chamber 4, the population of fruit flies will continue to increase until the fruit is consumed. At this point the remaining fruit flies will die if not released.