Population Change: Fox, Mice, and Seeds

 

STUDENTS WILL BE ABLE TO:
- Demonstrate that the populations of different organisms connected in an ecosystem change with respect to each other over time.
- Use mathematics to study population change over time.
- Examine feedback mechanisms that limit population growth.

GUIDING QUESTION: How do interactions between individual organisms affect entire populations?

MATERIALS:
- Data sheet (one per class)
- Graphs (one per student)
- Pennies to identify foxes or belts for mice to wear as tails

CLASS ACTIVITIES:
1. This activity is best done outdoors, in a gym, or other open space where the entire class can spread out, run, and make noise. Gather class in a large circle and explain the rules.
2. The class is going to be divided into three groups: Foxes, Mice, and Seeds. About half the class should start as seeds, then 2/3 of the remaining students can be mice, and the last few can be foxes. For a class of 22, the numbers break down to about 12 seeds, 7 mice, and 3 foxes. These numbers are variable and will fluctuate over the course of the activity. The activity consists of several rounds where each organism is given time to eat their food source. Mice can be identified by tucking strips of cloth into their waistbands as tails, or foxes can wear pennies to distinguish themselves. If you have no identifying props, set up distinct visual or audible signals for each animal; for instance, mice squeak or could hold up their hands to make pointy ears.
3. After dividing the students into foxes, mice, and seeds, record the number of each. These are your initial population numbers. Line students up at one end of the field. First let the seeds go out and "blow in the wind." Tell them to find a place to "plant themselves." Once they have found their spot have them crouch down and repeat over and over "I'm a seed, I'm a seed, etc…"
4. Once the seeds are in their position, allow the mice to run out and find a seed to eat. Only one mouse per seed! Once a mouse finds its seed, it should crouch down next to the seed and link arms with it. The mouse is then hiding with the seed, and cannot be eaten by a fox.
5. Wait a few seconds after releasing the mice, and then release the foxes. The hungry foxes will need to hurry to catch a mouse, before the mice find their seeds, and are safe. Once a fox catches a mouse they should to link arms and freeze.
6. After each group has been released and enough time has been given for the foxes to have an opportunity to catch a mouse, tell them all to freeze and to return to the start line standing next to whomever they were able to eat.
7. Now you need to tally the results. Separate the mice that ate a seed. Those seeds now become a mouse because they contributed energy to the mouse population. Make sure the seeds that just became mice understand how to be a mouse.
8. Next separate the foxes that ate a mouse. Those mice are now foxes because they contributed energy to the fox population. Make sure the mice that become foxes understand how to be a fox.
9. Separate any seeds that did not get eaten and any mouse or fox that did not catch food. Explain that the mice and foxes that did not get food now become seeds because they died and then decomposed, thereby helping new seeds to grow. (Give your students a chance to explain how this decomposition could help new seeds grow.) Make sure the new seeds understand how to be a seed.
10. Finally, record the new numbers of foxes, mice, and seeds.
11. Repeat this as many times as you can. This activity is most effective if there are at least 5 rounds played.
12. After you have had enough rounds, split the students into groups to graph the change in populations over time.
13. As a class, discuss the results of the activity. What changes did they observe? Was the system sustainable? How do foxes, mice, and seeds coexist in actual ecosystems?