BIOL 100 Lab 2: Optimal Foraging Behavior Simulation: Group vs. Solitary
Foraging Under Different Food Distribution Patterns
I. Learning Objectives
• Understand some basic principles regarding optimal foraging theory
• Participate in testing hypotheses regarding optimal forging theory
• Demonstrate how solitary or group foraging efficiency is affected by different
patterns of food distribution
A calculator or computer with Microsoft Excel will suffice.
The demands of food acquisition exert strong selective forces on the anatomy,
physiology, and behavior of animals. Natural selection for efficient foraging affects
“decisions” about prey choice, patch choice for foraging, patch exploitation strategy, and
foraging group size (solitary versus group foraging) (Krebs 1978). It has been widely
demonstrated that food abundance and distribution (along with predation) are the primary
determinants of foraging behavior (e.g., Caraco et al. 1980, Pulliam and Caraco 1984).
Indeed, previous studies suggest that when food is approximately evenly dispersed in an
environment, solitary foraging yields a higher energy return per unit time (or less time to
acquire a set amount of energy) (Verbeek 1973). Alternatively, when food is clumped,
group foraging is more efficient (Zahavi 1971, Krebs et al. 1972).
This exercise is intended to provide experimental data to test hypotheses regarding
optimal foraging behavior (group or solitary) in environments with different food
distributions. Specifically, the exercise tests the hypotheses that widely dispersed food
favors solitary foraging and that clumped food distribution favors foraging in groups
(Cody 1971, 1974; Krebs et al. 1972.).
During the fall and spring semesters when I teach BIOL 100 on campus, this lab
exercise attempts to simulate and test these non-intuitive concepts by letting students
serve as “foragers” searching for “prey.” The foraging environment is the classroom,
prey are colored note papers attached to the underside of chairs on the lab, and students
will serve as predators. What I intend to have this online class do is summarize data
obtained from a fall semester class (e.g., generate means and standard deviations for data
and graph the data) and then interpret those data.
Four basic trials were conducted in this exercise to test the following hypotheses:
Hypothesis 1 – There should be no difference in time required to locate and capture prey
necessary to meet energy requirements between solitary and group foragers when food is
evenly (approximately) distributed in an assigned space.
Alternative Hypothesis 1a – Based on theory presented above, solitary foragers should
require less time to locate and capture prey than group foragers when food is evenly
(approximately) distributed an assigned space.
Hypothesis 2 – There should be no difference in time to acquire prey needed to meet
energy requirements between group and solitary foragers when food is patchily
distributed (clumped) an assigned space.
Alternative Hypothesis 2a – Based on theory presented above, group foragers should
require less time than solitary foragers to acquire prey to meet needed energy demand
when food is patchily distributed (clumped) an assigned space.
V. Trials that were Conducted during a Typical Fall Semester Class
For Trial 1 (solitary foragers; food evenly dispersed), 12 sticky notes (all of a
single color, e.g., blue) were placed in a widely dispersed (pseudo-uniform) pattern on
the underside of chairs in the laboratory classroom. Nine student volunteers were
gathered outside the foraging patch (e.g., at the front of the class). Other students acted
as timekeepers. (Note: The nine student volunteers do not know where the sticky notes
are located. On a set signal, the student foragers began searching for food (sticky notes)
in the foraging patch (set of chairs). Once a student has found and “captured” a food item
(i.e., met their daily energy need) he/she/they left the foraging patch. Total elapsed time
from beginning of search until a prey item was captured was recorded for each student
For Trial 2 (group foraging, food evenly dispersed), 12 sticky notes (of a different
color, e.g., yellow) were distributed in a widely dispersed pattern in the classroom.
Again 9 student volunteers were gathered outside the foraging patch. To simulate group
foraging, students were grouped into 3 groups of 3 individuals. Group integrity was
maintained by requiring students to hold hands through the foraging bout. To mimic
within group dominance hierarchies and possible interference during prey capture,
student groups had a dominance hierarchy assigned (e.g., by student height). Subordinate
individuals were to pass any prey item they captured to the next highest-ranking
individual in the group until all (if any) higher-ranking individuals had been fed. Once
all members of a group had obtained 1 prey item, the group left the patch. Time from
onset of foraging until each individual within groups captured a prey item was recorded.
Again, to simplify, only total elapsed time from initiation of foraging until the last
individual locates a prey item was recorded.
To test hypotheses regarding solitary and group foraging efficiency when food is
clumped also required 2 different trials. For Trial 3 (solitary foraging; food clumped) 12
sticky notes (all of a single color, e.g., green) were placed in a clumped distribution
throughout the classroom foraging environment. The sticky notes were distributed in 4
clusters with 3 prey items in each cluster (for each cluster, 3 sticky notes were placed
under a single chair). Nine foragers searched individually for prey and total elapsed time
was recorded for each forager. For Trial 4 (group foraging, food clumped), again sticky
notes (e.g., pink) were distributed in a clumped distribution as in trial 3. Nine student
foragers were arranged in groups and foraged under the rules described for trial 2 (e.g.,
students were grouped into 3 groups of 3 individuals).
To prevent “information transfer” (sensu Zahavi 1971), all sticky notes were hidden
prior to student entry into the classroom. Additionally, having different students act as
foragers in each trial should reduce errors associated with learning patch characteristics,
search image development, etc. Care was taken to prevent mistakes in prey choice
(wrong color of sticky notes).
The “raw” data for each of the trials presented above are presented in Table 1 on page 5.
Using these data, you are expected to do the following:
1. Calculate means and standard deviations of foraging times for the different trials.
Include these values in your lab assignment that you turn in to me. You should then be
able to use the means and standard deviations to create a graph using Microsoft Excel
that visually compares the efficiency of the four trials. Suggestions: The two variables
that you need to put on your graph are: 1) average time to capture food (in seconds) and
2) the pattern of food distribution (evenly distributed versus clumped). Make sure you
know which variable is dependent (goes on the y-axis) and which one is independent
(goes on the x-axis). You will need to use different colors to distinguish between group
and solitary foragers on your bar graph. You will need a legend to distinguish solitary and
group foragers. (In that respect, your graph will be similar to what was done to
distinguish among damaged and undamaged treatments in the example graph – Figure 1below. Of course, the axes for your data summary will be labeled differently, you will
have a different legend, and a different figure caption.)
As indicated above, be sure to include the standard deviation error bars for the
mean values presented in your graph. The graph should be accompanied by a caption,
describing what is being depicted in the graph. Recall one of the YouTube videos I
provided for you about using Excel to make a bar graph with error bars:
https://www.youtube.com/watch?v=G10_qGcuELA The graph you need to create is a bit
more complex (e.g., you need to convey types of foragers and types of food distribution).
This YouTube video (beginning around 6:45) should be helpful to you in this regard:
https://www.youtube.com/watch?v=s3_hcCQGc50 I have also posted a file to
Blackboard with helpful hints on making a graph for this lab assignment.
The example graph below should give you ideas about how to display the data from the foraging
trials. Think about how to properly label your x- and y-axes and what should be labeled in the
legend. Don’t forget to include a figure caption below the graph that summarizes what is being
displayed in the graph.
Figure 1. Root:shoot ratios (mean+SD) of Ascepias syriaca plants for undamaged and
damaged treatments at low and high nutrient concentrations.
2. Answer the following questions: A) Do the data you summarized meet or adhere to
expectations based on what is known about optimal foraging theory? Explain in a couple
of sentences. In other words, do the data support the foraging strategies that are predicted
when food is evenly distributed and clumped? (You may need to go back and read the
first two pages of this lab to effectively answer this question. Please note that the faster
the foraging time, then the more efficient is the foraging strategy.) B) What are some
concerns you have with this type of classroom experiment? (Re-read the experimental
protocol on p. 2-3.) How would you avoid or improve on these concerns, if you were to
conduct your own experiment? (Here I want you to think about things you would
implement if you were to redo this experiment on a lab setting.)
VII. Due Date
This assignment must be emailed to the instructor via by 4:59 pm on 9/14.
VIII. Final Instructions
You should submit (=email) this lab assignment (as you would all other lab
assignments) as a Word document. (Recall that it is easy to copy a graph from Excel and
paste it into a Word document.) Your Word document should have: 1) the mean+SD for
each trial; 2) the appropriately labeled graph summarizing these data; 3) Address the two
questions that were posed. Your file must be named in the following manner: your last
name and the number of the lab assignment. For example: Smith Lab 2.docx.
Table 1. Foraging data obtained by BIOL 100 students for solitary and group foragers
with different food distributions (food evenly dispersed or clumped). All values are in
St dev ________
Caraco, T. 1979. Time budgeting and group size: a test of theory. Ecology 60: 618-627.
_____., S. Martindale, and H. R. Pulliam. 1980. Grouping: advantages and
disadvantages. Nature 285: 400-401.
Cody, M. L. 1971. Finch groups in the Mohave Desert. Theor. Pop. Biol. 2:142-148.
_____. 1974. Optimization in ecology. Science 183: 1156-1164.
Krebs, J. R., M. H. MacRoberts, and J. M. Cullen. 1972. Grouping and feeding in the
great tit Parus major: an experimental study. Ibis 114: 507-530.
Pulliam, H. R., and T. Caraco. 1984. Living in groups: is there an optimal group size?
Pages 122-147 In J. R. Krebs and N. B. Davies, eds. Behavioral Ecology: An
Evolutionary Approach. Second Ed., Blackwell Scientific Publications, Oxford,
Verbeek, N. A. M. 1973. The exploitation system of the Yellow-billed Magpie. Univ.
Calif. Publ. Zool. 99:1-58
Zahavi, A. 1971. The social behavior of the White Wagtail Motacilla alba alba
wintering in Israel. Ibis 113: 203
View of data and graph in Excel using a Mac computer
2. Click on the Column Menu when in Charts
and select Clustered Column
1. Organize your mean values for
solitary/group foragers and food
distribution (even vs. clumped) in the
3. Your graph should look
like this. Note you still
need to add standard
deviation values, as
instructed in Lab #1. For
help with this go to:
These are the design tabs when closed.
Click on them to open.
This is what the Excel spreadsheet looked like when I made the graph. When you click in the
graph (see blue arrow) itself you should be given option to Add Chart Elements (see red
When you click on the Add Chart Elements (see red arrow) a menu you drop down giving you
options to label x-and y-axis and make change to the legend
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