Optimal foraging theory is a principle that is often presented in the community ecology section of biology textbooks, but also can be demonstrated in the laboratory. We introduce a lab activity that uses an interactive strategy to teach high school and/or college students about this ecological concept. The activity is ideal because it engages students in a hands-on activity that teaches them a fundamental ecological principle; it can be completed in a short class period; and it utilizes a few inexpensive, easy-to-purchase supplies.
In this laboratory, we teach students about some of the concepts in community ecology, namely optimal foraging theory (Caraco, 1979; Pyke, 1984). The activity utilizes a hands-on approach, and it is designed to teach students that optimal foraging is a dynamic process.
We have conducted this activity at the undergraduate college level (nonmajor) for several years, but it would also work well at the high school level (perhaps with AP or other advanced learners) to teach fundamental community ecology principles. Students are successfully engaged in a hands-on activity that teaches the dynamics of optimal foraging. The lab can be completed in a 2- to 3-hour biology block, or it could be taught in one to two classroom periods. We have included a Teacher Procedures section that provides extension activities and ideas to modify this lab for a broader range of students. The materials are inexpensive and readily available at most retail stores. We have received strong positive feedback from the students who engage in this activity. Students report that the lab is fun, engaging, easy to follow, and easy to understand.
The goal of this lab is to introduce students to the concept of optimal foraging theory. In particular, students should be able to define key terms in community ecology and use those terms to explain optimal foraging theory. Finally, students should understand and be able to explain why optimal foraging is a dynamic process. Below, we provide a suggested introduction for students and instructions for teachers.
12 tablespoons (15 mL)
12 soup spoons (20–25 mL)
12 coffee scoops (1/8-cup, or 30 mL)
A 3 × 3 m indoor/outdoor carpet
1 set of dice
3 large plastic water containers (see Teacher Procedures)
24 plastic cups (16 oz, or 473 mL)
Triple beam balance or electronic scale
One goal of living organisms is to live and pass their genes to the next generation (i.e., reproduce). In this lab, you will be playing the role of YOU. You are acting as a “water-eater,” meaning that your food source is represented by the amount of water you collect. In this lab, water equates to food. For our purposes here, we will take a simple definition of a “niche” as the role an organism plays in its community; the habitat is the physical surroundings where an organism can usually be found. Unfortunately, there are now other water-eating species (i.e., your classmates) sharing your habitat.
Optimal foraging theory suggests that individuals will try to maximize their energy intake and minimize the energy they expend on obtaining food. Animals must balance the cost of foraging (i.e., search time, handling, etc.) with the energy value of the food/prey choice. This can be accomplished in many ways, depending on the abilities of the individual or species, the number of competing water-eaters, the prey consumed, the caloric value of the prey, the amount of time required to capture and consume the prey, risk of injury from the prey, and the presence of predators in the feeding grounds. Optimal foraging is a dynamic aspect of ecology that should be expected to change with locality, season, and different environmental conditions.
In today’s lab, you will attempt to obtain food (represented by the water at each feeding ground) in order to survive and reproduce. You will need to maximize the amount of energy that you take in your stomach (one cup will serve as your stomach). You will be foraging in a habitat with three different feeding grounds (A, B, and C):
At feeding ground A, you will use tablespoons to transfer water to your plastic cup. There are no predators, and the prey (i.e., water) is easy to catch. You can place your cup down beside the water container, but the cup can’t be touching the container (Figure 1).
At feeding ground B, the prey are much larger. You will use a 1/8-cup (30-mL) coffee scoop to transfer water to your plastic cup. There are no predators; however, the prey (i.e., water) is harder to catch. To simulate the difficulty of prey capture, your cup will be placed 2 m from the bucket and you will run back and forth to transfer the water (Figure 2).
At feeding ground C, the prey is medium sized. You will use a soup spoon to transfer water to your solo cup. The prey (i.e., water) is easy to catch. However, at the end of each feeding period, one of you will be killed by a predator. You can place your cup down beside the water container, but the cup can’t be touching the container (Figure 1). The instructor will serve as the predator. This will be determined by rolling a die (see Teacher Procedure).
Choose a feeding ground. Keep in mind that if you do not like your chosen feeding ground, you can move to a different feeding ground at the start of the next round (NOTE: You cannot change feeding grounds during a round.) Also, the feeding grounds will not be refilled during a round, and with enough “predation” it is possible for these feeding grounds to run out of water (i.e., food).
You will be given 1 minute to forage (i.e., collect water).
You need 200 g of water to survive a given year. Any extra grams of water consumed will be stored for the following year. When you have stored 500 g of water, you can reproduce. In the year following reproduction, you need an extra 50 g of water for each offspring you are raising (200 g for you and 50 g for each offspring).
If you do not forage at least 200 g of water in a given year, you die. You then start out the following year as a new water-eater with no stored energy. If you do not forage enough to support your offspring, they will die. Also, if you are eaten by the predator, you die and so do your offspring.
No direct competition will occur between water-eaters (no fighting or stealing of captured prey from your fellow classmates).
At the end of the minute, you will weigh your cup to determine the amount of water you consumed (in grams). Record your data in the Feeding Chart provided (Table 1).
The winner will be the student who produces the most offspring in 10 years.
Grams consumed in current year.
Total grams available = Consumed + Stored. There are no stored grams in year one, in a year after you have died, or in a year after you have reproduced.
0 offspring = 200, 1 offspring = 250, 2 offspring = 300, etc.
Stored = Total – Cost of survival. You can reproduce when this number reaches 500.
Prior to the lab, the instructor should set up the three feeding grounds. We often conduct this lab outdoors during the warmer months. If the lab is run indoors, we place the water buckets on outdoor green carpeting that measures 3 × 3 m and can be purchased at any home-improvement or hardware store. Be sure to provide enough space for students to gather around each water station, and enough space between feeding grounds to prevent crowding. For the water stations, we use shallow-sided plastic containers measuring about 46 cm long × 38 cm wide × 13 cm high. To enforce the idea of limited food availability, we fill the containers only half full of water.
Feeding Ground A
Fill one of the water containers and place several tablespoons next to the bucket. The number of spoons will depend on your class size.
Feeding Ground B
Fill another water container. Place a strip of tape 2 m away, running parallel with the side of the container. Place several 1/8-cup coffee scoops along the strip of tape. This is where students will place their plastic cups.
Feeding Ground C
Fill the last water container, and place several soup spoons next to it.
This activity is designed to work well with up to 30 students. We suggest adding additional feeding grounds and supplies (i.e., spoons, etc.) for class sizes larger than 30. We use inexpensive electronic scales for students to weigh their cups. In general, you will need one electronic scale per 10 students.
At the beginning of the lab, we spend some time introducing students to important terms. We make sure to explain that optimal foraging theory (Pyke, 1984) is one of the key concepts introduced in this lab, and the instructor should make the dynamics of the process clear to the students. It is important to communicate that foraging strategy may change depending on the situation at hand. For instance, a water-eater that is close to reproducing may attempt to limit the chances of predation by choosing a low-risk foraging ground.
Depending on the student level, the instructor may want to incorporate the competitive exclusion principle, or Gause’s hypothesis (Gause, 1932; Gilbert et al., 1952; Pulliam, 1985; McPeek, 2014), which states that two species cannot occupy the same niche within the same habitat. One species will always outcompete the other. The student’s job is to drive these other organisms off. As a water-eater, students are not equipped to fight; instead they must defeat their competitors by out-reproducing them. To do this, students must be the most efficient water-eaters in the lab. This means that each year, students will attempt to eat more food in order to survive and out-reproduce all of the competition. Remember that in any competition, there is a winner and a loser. To win this competition, the student must become an optimal forager.
Because the goal of today’s activity is to reproduce, it is important to know about r/K selection theory (MacArthur and Wilson, 1967; Reznick et al., 2002), which suggests that there is an evolutionary trade-off between quantity and quality of offspring. R-selected species devote lots of energy into making a lot of offspring but devote little energy into caring for them. By contrast, K-selected species have fewer young but devote lots of energy into caring for them. In today’s lab, the students are a K-selected species.
In addition to introducing the key concepts, the instructor should introduce the students to the procedure. Be sure to explain each feeding ground. Remember, feeding ground A does not have any predators that can kill and eat a water-eater, but the energy value of the food is very low (i.e., tablespoons). Feeding ground B does not have a predator, but the energy value of the food is much greater (i.e., 1/8-cup coffee scoops, but students have to run). Feeding ground C has a predator, and the energy value of the food is average (i.e., soup spoons). At this feeding ground, one student will die at the end of each round. At the end of each round, the instructor should have one student from this feeding ground roll a die. Students will count off counterclockwise to determine who has died in this round. Here are two potential scenarios. Let’s say you have four students foraging at this feeding ground. At the end of the round, one of the students rolls a 2. The second person to the left of the die-roller would be dead. Alternatively, let’s say you have four students and they roll a 6 at the end of the round. In this case, you will continue counting counterclockwise around the group until you reach a 6. Students that die start over in the following round as a “new” water-eater.
It is a good idea to use a few examples to show students how to complete the chart (Table 2). Let’s imagine that a student weighs his cup at the end of round 1 and has only collected 180 g of water. It requires 200 g to survive; therefore, the student has died in round 1. The student starts over in round 2 and collects 225 g of water. In this case, there would be 225 consumed, and a total of 225. After subtracting 200 g, the student has 25 g in the stored column. In round 3, the student collects 250 g of water. So there would be 250 consumed, and a total of 275 (250 + 25 from the stored column). After subtracting 200 g, the student now has 75 g in the stored column. In round 4, the student collects 190 g. There would be 190 consumed, and a total of 265 (190 + 75 from the stored column). After subtracting the 200 g, the student now has 65 g in the stored column. As you can see, the stored column serves as a running total. Finally, remember that a student needs 500 g of stored energy in order to reproduce. In the year following reproduction, a student must collect enough water for him and his offspring to survive (total of 250 for himself and one offspring).
|Year .||Consumed .||Total .||Cost of survival .||Stored .|
|Year .||Consumed .||Total .||Cost of survival .||Stored .|
The following are a few questions we ask students to explain:
What aspects of the environment influenced your foraging strategy (list at least three)?
There is a concept in community ecology called the “encounter-dilution effect.” It basically implies that there is safety in numbers (Caraco, 1979; e.g., herds, schools, and pods). Was this a factor in your decision to go to the feeding ground that contained the predator? Why or why not?
There is a concept of population ecology called the “ecological optimum,” which is the optimal population density (individuals per unit of space) that a habitat can support. This idea suggests that densities above the optimal population density have a negative impact on individuals. Was density of competitors a problem at any of the foraging grounds? If so, which grounds?
Draw a graph depicting time (x-axis) versus consumption (y-axis). Have the students offer possible explanations of the data outcome.
We thank Dr. Alvin Tubbs (Huntingdon College, Montgomery, AL) for his contributions to this effort.