Lab 30: Optimal Foraging — Procedure

  1. Simulating Foraging with Artificial Habitats and Prey
    • NOTE: The foragers will hunt for prey represented by pinto beans in four buckets of rice with varying prey densities. Without knowing what these densities are, foragers must obtain as many prey items as possible in as little time as possible.
    • HYPOTHESES: In this experiment, the experimental hypothesis could be that foragers will catch the most prey in the higher prey density bucket and also spend the most time foraging there. The null hypothesis would then be that foragers will catch an equal number of prey in each bucket and that foragers will spend an equal amount of time foraging in each patch.
    • To begin the foraging activity, record the names and role of each participant at the top of the student data collection sheet. NOTE: Before starting the experiment, the forager is allowed to become familiar with the foraging process – the following steps are a practice round.
    • The forager should kneel or sit in front of the average density bucket.
    • Once the timer says start, the forager may begin looking for the pinto beans representing the prey. The forager can spend as much time as they like foraging in this bucket.
    • Once a prey item is located, the forager must signal that one has been found and place the prey in the cup next to the bucket.
    • Once they believe they have acquired most of the prey in the patch, they should tell the timer to stop the time and the practice round is over.
    • To begin the simulation proper, the forager should sit or kneel in front of bucket A.
    • The timer must be ready to start the stopwatch.
    • The recorder should be ready to record the time each prey item is located, in addition to the time that the forager arrived at and left each bucket.
    • When all parties are ready, the timer should start the stopwatch and say “start”, and the forager should begin foraging. NOTE: The stopwatch will run through the rest of the round for buckets B and C.
    • As the forager signals finding pinto beans and places them in the cup next to the bucket, the timer should tell the recorder the time.
    • The recorder should then write the time in the student data collection sheet. Click Here to download Table 1
    • Once the forager has decided to move on to the next bucket, they should tell the timer “done”, and begin moving to the next patch.
    • The recorder should record the time the forager left and the time they arrived at bucket B in the student data collection sheet.
    • Repeat the same procedure for buckets B and C. Once the forager has completed the activity, it is time for the next forager to begin using the same procedure.
  2. Results
    • Before performing any data analysis, review the data collection sheet and compile your individual data for captured prey, foraging time, and travel time for each bucket in your student calculations table. Click Here to download Table 2
    • After this, calculate your individual capture rate for each bucket by dividing the number of prey captured by the sum of the foraging time and travel time and record these values in your table. Individual capture rate = Number of prey captured / (foraging time + travel time)
    • To calculate your Giving-Up-Time or a GUT for each bucket, subtract the time that the last prey item was acquired from the time you left the bucket. GUT = time forager left bucket - time last prey item acquired
    • Next, calculate the mean GUT for your foraging group and record the values in your table.
    • Finally, calculate your scaled GUT for each bucket by dividing the bucket GUT by your group's mean GUT. Scaled GUT = Bucket GUT / Group mean GUT NOTE: The scaled GUT will allow class data to be pooled later on without differences in individual foragers skewing the data.
    • The instructor should now compile the data into the classroom spreadsheet. Click Here to download Table 3
    • Plot a bar graph of the average number of prey collected in each bucket. On the x-axis, A should represent the low prey density bucket, B should represent the medium prey density bucket, and C the high prey density bucket. Plot the y-axis as the number of prey items caught.
    • Next, plot the graph of the class average scaled GUT, where the x-axis represents the buckets with varying levels of prey density and the y-axis shows the values for the average scaled GUT.
    • Plot a third graph of the average time spent foraging in each bucket.
    • Now review the Marginal Value Theorem (MVT) from the concepts video and examine the three graphs that you generated from your class data. Take note of whether the graphs conform to the predictions of MVT.