Topic 5: Evolution
IB Bio HL/SL
Natural Selection Lab
Introduction:
Within every ecological community there exists a variety of several species. In stable communities each of these species tends
to maintain a relatively stable population size, particularly when viewed over the long term. This condition is known as
equilibrium. However, during times when environmental conditions fluctuate, a new equilibrium must be established. This lab
will explore (simulate) how the forces of natural selection operate to favor certain phenotypes while limiting the success of
others as a new equilibrium is established. In this experiment four different prey species (kidney beans, small red beans,
chickpeas and green beans) and three different predator species (students equipped with a cup and a plastic knife, fork or
spoon) will begin at equal levels and as the forces of natural selection act on each, a new equilibrium will be established. The
overall goal of this simulation will be to observe the process on natural selection as new population levels are established.
From “The Natural Selection of Forks and Beans”
http://www.accessexcellence.org/AE/ATG/data/released/0279-MikeBasham/index.html
Procedure:
Pre-lab set up (already completed)
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Count out 250 of each prey type (kidney beans, small green beans, chickpeas and lentils) and place in individual,
labeled containers
Lay out bench mat material on 2 lab benches
Set up 2 forks, 2 knives and 2 spoons and a stop watch at each of the lab benches
Lab
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Divide into 3 groups of 6 (try to keep groups as even as possible)
Proceed to a lab bench that has the activity set up on it
Divide the utensils (forks/knives/spoons) among the group members
Each group member should take a cup
Pour the “prey” species from their containers on to the lab bench (ON THE COVER MATERIAL) and mix them all up
evenly
Start the timer. “Forage” (i.e. use your utensil to gather as many prey as possible into your cup) for 30 seconds.
Record your data and then move on to generation 2. Every generation the proportion of prey and predator species will
change. Use the formulas provided on the following sheets to determine the numbers of predators and prey for the
next generation.
*NOTE – there are extra utensils and beans at the back of the room*
Foraging:
Each predator will be allowed to forage for 30 seconds. Each prey item must be scooped up onto the utensil and then placed
into the cup which must be kept upright at all times. "SHOVELING" THE PREY ITEM INTO THE CUP IS NOT ALLOWED.
Complete the hypotheses below before foraging:
Hypotheses:
Which prey species do you predict will be captured the most? Why?
Which prey species do you think will be captured the least? Why?
Which predator species do you think will capture the most number of prey? Why?
Which predator species do you think will capture the least number of prey? Why?
Topic 5: Evolution
IB Bio HL/SL
DATA COLLECTION
Qualitative Data
Table 1. Description of prey and predators used in the simulation
Description of Prey
Kidney beans
Green beans
Chickpeas
Lentils
Description of Predators
Fork
Knife
Spoon
Quantitative Data
Table 2. Initial population counts for prey and predators generation one.
Prey type
Kidney beans
Green beans
Chickpeas
Lentils
Total
Predator type
Knives
Forks
Spoons
Total
Number (± 2)
250
250
250
250
1000
Number
2
2
2
6
FORAGE FOR 30 seconds!!
Table 3. Number of prey captured per predator in generation one.
Predator
Knife 1
Knife 2
Fork 1
Fork 2
Spoon 1
Spoon 2
Total
Kidney Beans
Number of prey captured
Green beans
Chickpeas
Lentils
Topic 5: Evolution
IB Bio HL/SL
Table 4. Generation one predation counts after foraging for 1 minute.
Type of prey
Kidney beans
Green beans
Chickpeas
Yellow split peas
Type of prey
Kidney beans
Green beans
Chickpeas
Yellow split peas
Starting number (±2)
250
250
250
250
Total number captured by all predators (±2)
Prey that avoided predation
Sample Calculation
Number of kidney beans avoiding predation after generation one.
Starting number – number captured = number avoiding predation.
250 kidney beans - ____________ total kidney beans captured = ____________ kidney beans avoiding predation
Table 5. Number of prey that avoided predation
Type of prey
Kidney beans
Green beans
Chickpeas
Yellow split peas
Total number avoiding predation
Number avoiding predation (±2)
SETTING UP THE NEXT GENERATION
Generation 2: Initial Prey Population Counts
It will be necessary to determine the population size for both predators and prey for the next generation. The total number of
prey species will remain constant from generation to generation i.e for 4 prey species the total number will always be 1000.
Sample Calculation
Kidney bean population size for generation two =
[Number of kidney beans that avoided predation  total number of all prey species that avoided predation] x 1000
[_______________________ _______________________] x 1000 = ________________ kidney beans for generation two.
Table 6. Prey population counts for generation two
Prey type
Kidney beans
Green beans
Chickpeas
Number (± 2)
Yellow split peas
Total
*Note – now that you have your NEW prey counts for generation 2, you may have to go to the back of the room and get some
more of one type of bean and return some of the other types of beans*
Topic 5: Evolution
IB Bio HL/SL
Generation 2: Initial Predator Population Counts
Sample Calculation
Knife population size for generation two =
[Total number of prey captured by all knives  total number of prey captured by all predator species] x 6
[_______________________ _______________________] x 6 = ________________ knives for generation two.
Table 7. Predator population counts for generation two
Predator type
Knives
Forks
Spoons
Total
Number
*Note – now that you have your NEW predator counts for generation 2, you may have to go to the back of the room and get
some more of one type of utensil and return some of the other types of utensils*
Set up the new prey and predators and on the bench mat for the next generation and forage again for
30 seconds!!
Table 8. Number of prey captured per predator in generation two.
Predator
1
2
3
4
5
6
Total
Kidney Beans
Number of prey captured
Green beans
Chickpeas
Lentils
Table 9. Generation two predation counts after foraging for 1 minute.
Type of prey
Kidney beans
Green beans
Chickpeas
Yellow split peas
Type of prey
Kidney beans
Green beans
Chickpeas
Starting number (±2)
Total number captured by all predators (±2)
Yellow split peas
Type of prey
Kidney beans
Green beans
Chickpeas
Yellow split peas
Total number avoiding predation
Number avoiding predation (±2)
Topic 5: Evolution
IB Bio HL/SL
SETTING UP THE NEXT GENERATION
Generation 3: Initial Population Counts
Use the same formulae to determine the population sizes of the predator and prey for generation 3 as you did for generation 2.
Table 10. Prey population counts for generation three
Prey type
Kidney beans
Green beans
Chickpeas
Yellow split peas
Total
Number (± 2)
Table 11. Predator population counts for generation three
Predator type
Knives
Forks
Spoons
Total
Number (± 1)
NO MORE FORAGING
Conclusions
1) By generation 3, which prey species had been captured the most? Give a reason for your answer.
2) By generation 3, which prey species had been captured the least? Give a reason for your answer.
3) By generation 3, which predator species had the most survivors? Give a reason for your answer.
4) By generation 3, which predator species had the least survivors? Give a reason for your answer.
6) How do the results from this lab represent the occurrence of Natural Selection?