Natural selection is an important process underlying the theory of evolution as proposed by Charles Darwin and Alfred Russell Wallace. "Survival of the fittest", as the outcome of natural selection is sometimes called, is fairly easy to comprehend, especially if we think of the success in breeding dogs or horses or cattle or many kinds of plants to suit our purposes. Humans artificially select the traits they want in the population. Natural selection is sometimes harder to imagine, although it is a fairly straightforward concept. What is more difficult is an appreciation for the effects of natural selection within a population over time.

PURPOSES: The purpose of this lab is to set up a simple simulation of natural selection in a predator - prey system. Students will act as the predators and the effects can be seen, after only a few generations, of one type of predator or prey having an advantage over another; or in other words the effects of natural selection can be observed!

MATERIALS: Four colors of beans

Five feeding structures (forceps, hand, spoon, fork, knife)

Cups (paper or plastic)

Eager and hungry predators (BIO 130 students)

PROCEDURES: Students will feed individually.

- Each student will be assigned to one of the structural feeding variation groups; that is, predators which feed using forceps, hand, spoon, fork, or knife. These variations represent genetically fixed differences in the population. All individuals have identical mouths (cups).

- 50 beans of each color (200 beans total) will be spread out in an area representing the habitat of these organisms. Mix the colors well (no patches of just one color beans)

- HYPOTHESES: predict the relative success of each predator and prey; 1 =best, 2 =second best…

Predators: Prey:

Forceps _________ white ___________

Hand _________ speckled ___________

Spoon _________ black ___________

Fork _________ lentil ___________

Knife _________

- Begin hunting when the instructor says to begin and continue until you are told to stop. The prey (beans) must be picked up with the feeding apparatus (forceps, hand, spoon, fork, or knife) and placed in the mouth (cup, please don't really eat the beans). No scraping or pushing of the prey into the mouth is allowed. You must hold the bottom of the cup flat against the table. You may, however, dash in and pick up any prey being pursued by another predator. Don't hesitate to intrude…any hungry natural predator would "go for it!"

- When told to stop hunting, count and record the number of each type of prey you captured (tables are attached). We will total the "kills" by type of feeding apparatus for each type of prey. This will allow us to see which predators were most successful (measured by success in capturing prey) and which prey were most successful (measured by NOT being captured).

- The predator groups will be reconstructed for the next generation. Predator types which capture fewer prey than others are not successful hunters and natural selection might remove them from the population. After two generations the least successful predator type will be considered extinct. After the third generation the least successful predator (of the remaining types) will again be considered extinct. Students that had those feeding apparatus will be assigned to other groups and will represent the offspring of the successful predator types.

- After each period of hunting the prey remaining in the prey population (those not captured) will be doubled to represent reproduction. The additional beans of each color will be added to the remaining population in the habitat.

- After each generation and the restructuring of the predator and prey populations, predators will again be allowed to hunt for a specified time period and the procedures will be repeated. This will be done for four generations.

- Data tables (attached) will be filled out as we work through the exercise. The tables, and analysis of the data, will be included in your lab report. Frequency calculation is explained below.
 
 

LAB REPORT: The lab report is due at the end of the lab period. You will turn in your summary tables and on separate sheet(s) of paper, answer the following questions:

1. Which prey variation (bean color) appears to be best adapted to the environment? Explain, based on your data, why that group is considered to be best adapted. Explain, in the "real world" (that is the world of beans) why this group is best adapted.

2. Which prey variation appears to be least adapted to the environment? Again, explain, based on your data, why that group is considered to be least adapted.

3. Which predator variation ("mouth" type) appears to be best adapted to feeding on this prey population? Explain, based on your data, why that group is considered to be best adapted.

4. Which predator variation appears to be least adapted to feeding on this prey population? Explain, based on your data, why that group is considered to be least adapted.

5. Write a statement explaining natural selection and how this simulation demonstrates the role of natural selection in populations (both predator and prey).
 
 

APPENDIX: HOW TO DETERMINE "SUCCESS:"

The success of a predator type is determined by how well it feeds; successful predators eat more than other predators and therefore survive and reproduce. Successful prey are eaten less frequently than other types of prey. These are measured by a percentage:
 
 

# beans a certain predator eats

________________________ x 100 = % of total predation

total # beans killed
 
 
 
 

The same calculation is done to determine prey success:
 
 
 
 

# beans of a certain color present after feeding

____________________________________ x 100 = % of bean population

total # beans present after feeding