Carrying Capacity

Objectives

• Assess survival needs and interactions between animals and the environment.

Materials

• Per Class or Group:
  timer
  whistle
  4 long ropes or several cones to delineate the playing area’s boundaries (Approx. 15m x 15m. the playing field size can be adjusted to accommodate the age and ability of the students)
  30 blue poker chips (one or two chips per student)
  30 green poker chips (one or two chips per student)
  2 hula hoops
  30 red bandanas (or other means of identifying the predators)
  30 green bandanas (or other means of identifying the prey)

Key Questions

• Season 1: Normal Predator-Prey Conditions What happened to the predator population after Season 1? What happened to the prey population after Season 1? Was there enough food and water to go around?
• Season 2: Too Much Predation What happened to the predator population after Season 2? What happened to the prey population after Season 2? Was there enough food and water to go around?
• Season 3: Not Enough Predation What happened to the predator population after Season 3? What happened to the prey population after Season 3? Was there enough food and water to go around?
• In nature, which prey are likely to get caught by predators? Which predators are likely to catch prey?
• When the resources are low (less prey for predators or less food and water for prey), which ones will succeed in reproducing?
• What animal species could this game represent?
• What is meant by “carrying capacity” of an area?

What To Do

Setup

1. Divide students into predators and prey. The relative numbers of each will depend on the conditions present (see Parts 1, 2, 3). Give the predators a red bandana to wear on their head. Give the prey a green bandana to wear on their head.
2. The playing field will have 4 boundaries: water, food, predator den (at one end of game area), prey shelter (at opposite end of game area).
3. In the middle of the water boundary, place blue poker chips within a hula hoop. These will represent portions of water for the prey.
4. In the middle of the food boundary, place green poker chips within a hula hoop. These will represent portions of food for the prey.

Game
Each season represents different sets of predator-prey conditions. The numbers are based on a class of 25 students.

Season 1: Normal Predator-Prey Conditions

1. The game starts with 6 predators and 19 prey.
2. The prey start as a group behind the shelter line, and the predators start as a group behind the den line. The game begins at the blast of the teacher’s whistle. The predators and prey will have 2 minutes to reach their goals.

The Predator’s Goal 

• The predator must catch a prey and bring it back to its den.
• It only catches one prey per round (since it takes a while to eat and digest it).
• If a predator does not manage to catch a prey, it dies of starvation and does not make it to the next season.

The Prey’s Goal

• The prey must grab a portion of water (blue chip) and a portion of food (green chip) before returning to its shelter to reproduce, all without getting caught by a predator.
• If there is still time, the prey can go back out and try to get more portions of water and food, but will this time grab the number of portions it needs for itself and its young (e.g. two portions of food).
• If the prey does not get enough food/water, it dies of starvation or dehydration and does not make it over the winter to the next season.

3. At the end of the round, the food and water chips are returned to their stations, indicating the renewal of the resource.

Season 2: Too Much Predation

1. The game starts with 15 Predators and 10 Prey.
2. Play the game as Season 1.

Season 3: Not Enough Predation

1. The game starts with 2 Predators and 23 Prey.
2. Play the game as Season 1 and 2.

Extensions

• Add in other features: As a group, the prey will choose a feature and a simple way to act it out. This will be made clear to everyone, including the predators. Examples of features include camouflage, the use of horns or tusks, etc. When a prey uses its feature, the predator must freeze for 3 seconds giving the prey time to escape. Have the prey practice their feature and the predators practice freezing.
• The Prey’s use of feature: If a prey sees a predator approaching it, it can use its feature to defend itself. The predator must freeze for 3 seconds, giving the prey time to escape. The prey cannot use its feature after the predator has tagged it. The prey cannot use its feature while drinking nor eating. This mimics how prey must often let their guard down momentarily while eating and drinking.
• Add one or two prey that were born without the special feature that the others have:
• How would it affect their chances of survival?
• What special features would you want if this game was set in the woods? On a beach? In the snow?
• At the beginning and end of each round, write down the number of predators and prey (including offspring). Graph the results when you return to class.
• Consider carrying capacity in familiar terms by considering a schoolyard “ecosystem”. What happens if only 3 students are outside at recess (e.g. you can use whatever you want, there is little sharing/waiting, but you can’t play kickball)? What happens if two other schools showed up and there were 300 more students outside at recess?