SUPPLIES

• 1 rope to make a circle on the ground

• 6 cups

• 6 spoons

• plastic baggies for separating the jelly beans

• 1 stopwatch for the TA

• colored jellybeans purchased from Southern Season

• 250 white
• 100 green
• 70 pink
• 130 yellow
• 50 orange
• for half of the classes, reverse the numbers of pink and yellow

PROCEDURES

This lab requires that the students remain relatively naive about the experiment until the data have been collected.   Explain some of the general principles at the beginning of the lab, but do not explain the experimental design until later.   The lab manual for the students does not include the experimental design.

The point of handling the jellybeans with a spoon is to make it impossible to handle more than one at a time.   Furthermore, the requirement that each jellybean must be carried to the edge of the arena makes it difficult for the searcher to locate more than one jellybean at a time (the Mouth presumably cannot remember exactly where other jellybeans are while handling one).   If all works as it should, Mouths will find and handle one jellybean at a time, with several seconds between jellybeans.

The point of the Stomach moving around the arena is to allow the Anus to throw the jellybeans back into the arena haphazardly and -- ideally -- not in front of any Mouth.   Make sure that a team does not throw jellybeans to its own Mouth!

For the success of this lab it is important to pay attention to two things.  

• Find an arena with grass long enough to make it somewhat challenging to see the jellybeans.
  

• Keep trials brief and run them in a carefully selected order:

  50 white and 50 watermelon green (1 minute total) -- conspicuousness

  100 white (2 minutes) -- training for specific search image (SSI)

  50 white and 50 orange (1 min or perhaps only 30 sec) -- test for SSI (both conspicuous)

For the test of an SSI, there is no easy way to determine the relative conspicuousness of the two colors used in the trials.   Consequently, it is important to reverse the color used in the training trial for half of your sections. Any trials beyond this number are likely to result in sequential influences of one trial on the next.   The searchers will start to develop unpredictable strategies.

To test for an influence of rarity, change searchers and then run these trials:

• 50 white and 50 watermelon green (1 minute) -- conspicuousness

• 50 pink and 50 yellow (2 minutes) -- test for antecedent preference

• 20 pink and 80 yellow (1 minute) -- test for rarity

The second trial above (test for antecedent preference) also serves to make the searchers aware of the presence of both colors in equal numbers in the arena.   It thus should prevent searchers from forming an SSI for the commoner color.

The results are best analyzed with Chi-squared Tests for goodness-of-fit to the expected proportions for random search.

ADDENDUM

This lab could be modified to investigate the influence of profitability and search times on foraging.   To do so, you would have to manipulate search times, handling times, and profits from different kinds of jellybeans.  

Profitability (energy/item) could be adjusted by awarding a different number of points for each color of jellybeans.   Search time could be influenced by the abundance or conspicuousness of each color.   Handling time would be more difficult to adjust.   One possibility is to have the Stomach walk different distances to reach the Anus (once around the arena or twice around, for instance) -- for the Stomach's movements to represent handling time the Mouth would have to wait until the Stomach returned   before it began searching again.   In this case, the labels Mouth, Stomach, and Anus are not really appropriate.   Better labels would be Claws, Mouth, and Digestor (combined Stomach/Anus).  

Any TA who feels ambitious can give this exercise a shot!   See faculty if you would like to brain-storm procedures.