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Grade Level (s): 8
Introduction: The Theory of Natural Selection proposed by Charles Darwin, is one of the most important theories to modern biologists. The four tenets of evolution by natural selection are summarized as follows:
- Overproduction: Organisms are capable of producing large numbers of offspring.
- Variation: Offspring have varying physical and heritable traits.
- Competition: Offspring must be able to compete for limited resources in their environment.
- Differential Reproduction: Those offspring best suited to exploit resources in a particular environment will leave more offspring to future generations than those less well adapted.
Natural selection can be observed in butterflies that use warning (aposematic) coloration indicating its distaste to predators; the well developed eyesight and olfactory senses of a shark that makes it an efficient predator; the camouflaging (cryptic) coloration of a moth against the bark of a tree, are all are believed to have occurred as a result of selective pressure over thousands of years.
True speciation takes thousands of years, but, microevolution, adaptation of individuals within populations, can be observed in a predator - prey experiment.
Students will assume the role of a marine predator and attempt to capture as much prey as possible in order to prevent extinction of their species
Students are to consider:
- The effectiveness of the prey's coloration to prevent it from being captured.
- The effectiveness of the predator's feeding apparatus at allowing it to capture enough prey to survive and produce offspring.
The activity will demonstrate the changes in the frequency of traits over time in a population in response to whether the trait is advantageous to survival or detrimental to the members exhibiting these traits.
Learner Objectives:
- Students will demonstrate that camouflage is a key factor in species survival and natural selection.
- Students will observe that species adaptations are critical to exploit the environment for survival.
Sunshine State Standards Correlation: Science: SC.F.2.4.3, Math: MA.D.1.3.1, MA.D.1.3.2, MA.E.1.3.1
Competency-Based Curriculum Correlation: Science: Sci.M/J3 II-4-B
Materials:
Large plastic tubs (1 per group)
Sand
Aquarium plants (plastic or real)
Shells
Water
Red beads (approximately 50 per group)
Black beads (approximately 50 per group)
White beads (approximately 50 per group)
Tweezers (5 per group)
Plastic forks (5 per group)
Plastic spoons (5 per group)
Small plastic cups (7 per group)
Medium plastic cups (1 per group)
Activity Procedures:
- Ask students to discuss the importance of color to the survival of certain species in marine environments.
- Students are to make a null hypothesis prediction and an alternate hypothesis before beginning the activity as to color of bead and its survival rate.
- Divide the class into groups of ten members.
- Each group should be supplied with a tub setup. The setup should recreate a marine environment. Use approximately one inch of sand and shells at the bottom of the tub half filled with water; anchor the plants in the sand or allow them to float in the water. Depending on class time limitations, tubs may be arranged prior to the activity or students may arrange them as part of the activity. Tweezers, plastic forks, plastic spoons, and small cups should also be at the group stations.
- Each member of the group will have specific jobs/tasks.
- One member (P) will be responsible for the prey population, one member (T) will be the timer, one member (C) will be the counter of captured prey, and
- one member (D) will record the data in Table 1. The remaining students will be predator members (PM), if not selected to be the first generation predator, remaining PM will record observations and interactions among predators and serve as offspring to the predator.
- P is to count out ten individuals of each color prey.
- Place all beads in the large container and mix thoroughly.
- All members of the group should have their backs turned away from the tub while member P sprinkles the prey into the tub.
- Three predator members of the group will select a different mouthpart (either tweezers, fork or spoon, but only one) and a small cup (mouth)
- The timer will tell the predators when to begin their 90 seconds hunt for prey.
- Using only the feeding apparatus, predators will place as many prey in their mouth (cups) as possible in the allotted 90 seconds.
- The timer will call time at the end of 90 seconds. Each predator will place their mouthparts in their cups give them to member C (counter).
- Member C will tally the colors and quantities of the captured prey and give the information to member D (data recorder).
Replenishing the Prey Population:
- To determine the number of survivors in each color class, use the following equation:
Population of living prey for each color at the beginning of generation (GP) - Number of kills of each color (K) = Survivors of each color (S) i.e., GP - K = S
- Calculate the proportion of surviving individuals available for reproduction in the next generation by using the following formula:
Example: If three (3) of the original ten (10) red beads were captured by predators, there are seven (7) red bead survivors. (10 - 3 = 7) If the total number of all beads captured was seven (7), then there are 23 total prey survivors still out there (30 - 7 = 23). The total number of red beads added to the next generation should be:
7/23 X 7 = 2.10 red beads added to the next generation
Replenishing the Predator Population:
- Calculate the number of each predator type surviving in the next generation with the following formula:
Example: If in the first generation, the tweezermouth predator captured five (5) of the total seven (7) beads captured by all predators, then the number of tweezermouths in the next generation will be:
5/7 X 3 = 2.13 tweezermouths
The number of tweezermouths has increased by 1.13. Sorry, you only get to add one (1) tweezermouth since 0.13 is not a whole individual. Let's see if there is more success in the next generation.
- Continue replenishing the prey and predator populations as calculated, if time permits, for two or three generations of natural selection.
Assessment:
- Which color prey seemed to be best adapted by means of camouflage to this aquatic environment? Which is the least adapted? Explain.
- Which predator seemed to be best adapted to successfully capture more prey? Explain.
- What other factors besides bead color could have affected the bead survival?
- What other factors besides mouthpart might have contributed to the predator's success?
- Did any predator or prey become extinct? Why or why not? If the answer is none, which possibly faced extinction over the next several generations?
- Did the experimental results support or refute the null hypothesis?
Activity Extensions:
- Using the internet and books, research predators and prey with unusual mouthparts and camouflage techniques that enable them to adapt to their environments successfully. Create a children’s book highlighting these creatures of evolution.
- The West Indian manatee is an endangered mammal that travels through canals, down rivers and into the ocean. How does this animal need to adapt to the changing environment to survive many generations to come? Write a persuasive letter to the animal convincing him/her that these adaptations are necessary for its survival.
- Research the peppered moth and describe the historical events that led to this animal’ s ability to adapt for survival.
Home Learning Activity:
Ask students to observe organisms (plants and animals) around the schoolyard or their homes. Describe the characteristics that make them successful for survival. Are there any features that put them at risk of possible extinction one day? Explain.
Vocabulary: natural selection, microevolution
References/Related Links:
Johnson, G. B. (1995). Evolution and Natural Selection . In K. Harris, L. Jegerlehner, K. Timp, J. Leland (Eds.), The Living World (pp. 171-196) Dubuque, Iowa: Wm. C. Brown Publishers
Krempels, D. (1998). Go Figure: Critical Thinking and Experimental Design in the Biology Laboratory. Unpublished, University of Miami Department of Biology.
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