Ancient Greek, Romans and Chinese all had philosophies which formed the basis for evolution. In the 1700’s geologists noticed that there was a pattern in fossils within rock strata, which led many to begin looking at the fossil record comparatively and seeing changes in organisms over time. By the 1800’s, evolution was becoming well studied and solidified in the scientific community; however, the mechanism of how it worked was heavily debated.
In the early part of the 1800’s a well-known French biologist named Jean-Baptiste Lamarck came up with the first full proposed mechanism for how evolution works. He stated that all organisms evolved based on the inheritance of acquired characteristics in a progression from simple to more complex forms. Although Lamarck’s ideas had many flaws, his was the most thorough hypothesis for the mechanism of evolution at the time. In 1859, Charles Darwin published his now world-famous book On the Origin of Species. In this book he proposed his theory of evolution by natural selection, now widely accepted within the scientific community as the primary means by which species evolve. Natural selection is defined as a difference, on average, between the survival and reproductive success of individuals with certain phenotypes compared with individuals with other phenotypes. When an organism has a trait that confers an advantage in survival and reproduction, that trait will be passed on to its offspring, and will therefore become more common in the population over future generations.
In nature we see rapid evolution by natural selection in predator and prey populations. This is because there is strong selective pressure for traits that help prey to escape or avoid predation (by camouflage, change in behavior, change in size etc…) as well as strong selective pressure for traits that allow the predator to continue to catch its prey.
In this experiment we will be simulating a predator population with varied methods for gathering prey and a prey population with different levels of camouflage and color.
Materials
White rice
Wild rice (a mix of colored rice)
Black beans
White beans
Red beans
Plastic utensils for each member in the group
Small cup for each member in the group
Stopwatch or timer on phone
Shallow pan or bowl
Lid or piece of paper to cover pan/bowl
Graph paper (or computer graphing program)
Procedure
A. Model how variation in a phenotypic trait affects a prey population over time.
Fill the shallow pan halfway with white rice. This represents your environment. Count out 40 black beans, 40 white beans, and 40 red beans. The beans represent different phenotypes of the same organism living in the environment.
Make sure the beans are mixed thoroughly into the environment. Mix by either by covering the pan with a lid and shaking for five seconds or stirring for ten seconds. Keep the lid on the pan or cover the pan with piece of paper until you are ready to start.
Read the following directions before you use your utensil to “hunt” prey for 60 seconds.
Start with your utensil (your “predator mouth”) on the table.
Simulate hunting by picking the prey (beans) out of the rice and putting them into a small paper cup (your “stomach”).
All phenotypes of beans have the same nutritional value, therefore you should eat any beans you see, not hunt for or eat just one particular color of bean.
You can only pick up one bean at a time.
You cannot scoop up the beans.
After picking up a bean, put your utensil down on the table and touch your forehead before picking up your chopsticks and foraging for more prey. This simulates the time it takes you to digest your prey.
All beans must be deposited in your cup. If you miss, you must collect your escaping prey and return it to your cup before continuing to hunt for new prey.
As soon as time is up, put down your utensil. If a bean is not in your cup when time is called return it to the environment.
After 60 seconds of predation, count the number of beans that have been eaten, and figure out how many remain in the population by subtracting the number eaten from the original 40. Record these numbers in Table 1.5.
We will assume a simple model where there is no death, and all individuals are able to produce one offspring that will survive to adulthood. Simulate a reproductive event by doubling the number of each color of bean remaining in the environment. Record that number in Table 1.5 as the start of the next generation.
Add the new beans (the “offspring”) to the environment. Mix them thoroughly into the environment following step 2 and repeat the prey hunting process. Repeat predation for four generations of prey.
In the activity questions section graph the number of beans of each phenotype in the population at the beginning of each generation.
Repeat the simulation, but this time place the beans into a new environment composed of wild rice.
Before you begin, write down your prediction and reasoning about which color beans will do well in this new environment.
Record your results in Table 1.6.
Graph your results on your graph paper.
PREDICTION: Make a prediction and provide your reasoning for which bean color will do better in the wild rice environment.
Activity Questions:
1. Graph the number of beans of each phenotype in the population at the beginning of each generation for white rice on your graph paper. See example below:
2. Graph the number of beans of each phenotype in the population at the beginning of each generation for wild rice on your graph paper. See example below:
3. In Part A, did one bean phenotype survive better? Why? What features or qualities did it have that helped it survive in this environment?
4. In Part A, how did the prey population change over the four generations? Did the percentage of each bean type eaten change over time?
5. In Part A, were there any variations in predator efficiency (the number of prey eaten in 60 seconds) between group members? What were the causes for this variation?
6. The simulation in Part A ended after four generations. What do you think would happen if the simulation continued for another four generations?
7. In Part A, you were instructed not to preferentially select one color bean or another. However, did you ever find yourself looking for one color over another? Why?
8. How did a different type of environment affect natural selection of the prey population? What happened when the prey was living in the environment made up of the darker wild rice compared to the white rice environment? Was your prediction correct?
9. What would happen if a non-visual predator moved in, such as one that hunts at night using smell? Would certain types of beans still have an advantage?
10. In this simulation, white or black beans were different variations within the prey population. What would be necessary to consider them separate species?
11. How realistic is the model for simulating predators and prey in Part A? Explain your reasoning.