Natural Selection (Shelly Magier)
Title: Natural Selection: Camouflage
Principle(s) Investigated: Natural selection
Grade 7
Evolution
3. Biological evoluation accounts for the diversity of species developed through gradual processes over many generations. As a basis for understanding this concept:
a. Students know both genetic variation and environmental factors are causes of evolution and diversity of organisms.
b. Students know the reasoning used by Charles Darwin in reaching his conclusion that natural selection is the mechanism of evolution.
Grades 9-12
Ecology
6. Stabilty in an ecosystem is a balance between competing effects. As a basis for understanding this concept:
c. Students know how fluctuations in a population size in an ecosystem are determined by the relative rates of birth, immigration, emigration, and death.
g*. Students know how to distinguish between the accomodation of an individual organism to its environment and the gradual adaptation of a lineage of organisms through genetic change.
8. Evolution is the result of genetic changes that occur in constantly changing environments. As a basis for understanding this concept:
a. Students know how natural selection determines the differential survival of groups of organisms.
b. Students know a great diversity of species increases the chance that at least some organisms survive major changes in the environment.
Materials:
Preparation:
1. Enough paper to punch out 60 dots per color, + additional dots (still need to test out optimal number) for dot reproduction. (Purchased at Michael's)
2. Hole punch (Invest in a good hole punch or your hand will suffer. Found a good two-hole model at Office Depot, but there are better electric ones. Or, put your students to work!)
3. Full sized piece of paper for each group of three (ideally) students. (Can use carpet squares, or fake turf instead of colored paper.) Pick at least two shades that match your dot colors.
4. Tweezers (Lab, 99 cent store had small salad tongs with four per package.)
5. Timing device (can use timer on phone, or can supply a timing device-- still not sure about the supplier
6. QUICKWRITE
7. DATA ENTRY WORKSHEET (Graphs already set up and ready to graph data entered by students)
Carrying out activity:
1. Each group of three students should have:
a. One piece of paper ("habitat")
b. One pair of tweezers.
c. One timing device.
d. One container of 60 dots of each color being used.
e. Access to a supply of extra dots of each color for reproduction.
f. A data sheet if data is not being entered directly into a spreadsheet.
h. Camera, or phone that can take photos.
Example of a data sheet
Circle your habitat color: Light Green, Dark Green, Grey, Orange, White
Trial interval (sec):
Procedure:
1. Work in groups of four.
Each group should have:
One full-sized piece of paper (green or orange)
One pair of tweers (bird's mouth)
One beaker (stomach)
One dot nursery
One timer
Open to Data entry spreadsheet
One person for each job listed below
Jobs:
1) Predator (bird),
2) Scientist (times each trial, counts the number of prey of each color left on the solid sheet of paper (“habitat”) and enters the data into spreadsheet),
3) Photographer to document population after each trial (TAKE PHOTO BEFORE PREY KEEPER ADDS OFFSPRING).
4) Prey keeper (initially distributes prey dots, and adds one dot for every dot that is left after the scientist has counted how many dots of each color are remaining on the solid sheet of paper.)
2. The predator looks away while the prey keeper spreads out all of the dots evenly on the full-sized sheet of colored paper (“habitat”).
3. When the scientist says “go”, the predator quickly turns around, and removes as many dots (“prey”) as possible in 30 seconds.
4. The scientist counts and records the number of prey of each color that are left on the solid sheet of paper.
5. The prey keeper adds one colored dot of the correct color for every dot of that color that is still on the solid colored sheet of paper. The dots on the paper have survived and live to reproduce! (Example: for every one orange dot remaining, and additional one is added to the habitat.)
6. Repeat steps 2-5 three more times. Record the outcome for each trial in the spreadsheet.
Student prior knowledge: The activity would be most useful if students had a good understanding that traits are passed from one generation to the next via genetic information encoded on DNA. If they understand this concept they will understand why an individual's ability to reproduce may be directly linked to the perpetuation of a certain phenotypes.
Explanation:
IMPORTANT NOTE: I took this directly from the source below. I do not have a website for this source. It is a good explanation of the concepts addressed in this exercise and I plan to work with it and modify it, but decided to use it for class today.
From COASTeam Aquatic Workshops: the Piedmont (Grade 3); a joint effort between the COASTeam Program at the College of Charleston and the South Carolina Aquarium – funded by the SC Sea Grant Consortium.
Detailed Information
Detailed Information gives more in-depth background to increase your own knowledge, in case you want to expand upon the activity or you are asked detailed questions by students.
"Individuals in a population of any species vary in many traits that are inherited from their parents. Since members of a species have the potential to produce far more offspring, or young, than the environment can possibly support with space, food, water and other resources, a constant struggle for existence among the varied members of a population (a group of interbreeding organisms, usually within the same species) is inevitable. Charles Darwin calculated that a single pair of elephants would have 19 million living descendants just 750 years later, provided that every descendent along the way lived to be 100 year old and had just six surviving offspring. But elephants and most other populations remain stable because most of the young animals generated by a species die without reproducing. The “winners” of this constant struggle for existence are those individuals with adaptations best suited to the local environment. Adaptations are body part or behaviors that help an organism to survive in its environment. Because of their special, inherited traits some individuals are likely to be better able to avoid predators, to find food or mates or to deal with climatic pressures. These individuals will tend to survive longer and leave more offspring than others in their species that have different and less successful adaptations1.
Natural selection is the process that occurs when individuals differ in their traits and the differences are correlated with differences in reproductive success. In a very real sense, nature “selects” the best varieties to survive and to reproduce. To illustrate this process, consider the following hypothetical scenario. Imagine a new species of snake in which most individuals have green body color, but some have greenish-brown body color. This hypothetical snake lives among the treetops in green foliage and is a master of camouflage. This high degree of camouflage allows the snake to escape detection by predators and prey. The snakes with green bodies are more likely to survive and reproduce than the snakes with greenish-brown bodies; they are more adeptly camouflaged. This particular type of snake thrives on eating tree frogs and does well for quite some time. Over time, however, pollution in the area decreases the tree frog population and the snakes are forced to move from the treetops down to the brown forest floor strewn with dead leaves to search for food. The snakes find that rats are fairly easy to catch and that they can survive by eating them. Which color morph is more likely to survive at this point? Those with greenish-brown body color; these snakes with more brown along their bodies would be better camouflaged than the strictly green snakes. Over time, if the snakes continue to feed among the dead leaves, you would expect those snakes with the most brown body coloring to survive because they would be the most camouflaged and would survive most frequently to reproduce. In this manner, nature “selects” the best-adapted variety to survive and reproduce, and thus to pass their genes onto the next generation.
In this activity students will model the process of natural selection. You can choose whether or not to explain the term to your students or whether it is simply enough to introduce the concept that those animals best adapted to their environment survive to produce more offspring."
Bibliography
Alcock, John. 1989. Animal Behavior. Sinauer Associates, Inc., Massachusetts.
Student Key Terms
· camouflage
· reproduction
· adaptation
· natural selection
Objectives
The learner will be able to:
· model natural selection through role-playing.
· observe, record, and graphically represent data.
· predict possible outcomes of the activity, and discuss how the outcomes differ from predictions.
Questions & Answers:
1. Why are white colored animals rare in southern California?
White colored animals are rare in southern California because white stands out against most habitat types found in southern California. As a result, individuals that are predominantly white may be preyed upon before they can reproduce. Predators that are white might be spotted by prey and as a result would be poor hunters. If an animal cannot eat, it cannot reproduce.
2. Why is counter shading a pattern of coloration that occurs in several different taxa of organisms that live in the ocean?
Counter shading is an effective method of camouflage in the ocean. If a predator is looking down upon you your dark back will likely blend into the darkly shaded ocean surrounding you. If a predator is looking up at you, your lightly colored underside will blend in against lightly shaded water (from light filtering through from the surface) surrounding you.
3. The southern Pacific rattlesnake has quite a bit of phenotypic variability depending on where the snake lives (up in the mountains vs. closer to the LA Basin for example). Southern Pacific rattlesnakes in the mountains tend to be wider and have a darker appearance than those closer to the LA Basin. How might this type of phenotypic variability have evolved?
The snakes in the mountains may be wider because snakes with a lower surface area:volume ratio may have been selected for so that they will stay warmer longer. The warmer they stay the longer they can hunt. The darker color may have been selected for due to differences in habitat type.
Applications of the principle of natural selection to everyday life:
1. Free market economics: It seems only natural for students to see the similarities between the principles associated with natural selection and those associated with free market economics. High school students may find it interesting to apply this idea of the survival of the fittest to discussions about the ebb and flow of the nature of business. They can use concrete examples of starbucks vs. the local coffee house, or WalMart vs. smaller local businesses. Students may want to consider the similarities and differences between these two principles. They can also begin to see that a free market system may resemble natural selection, but the system that we currently have in place is not actually a free market system.
2. Discussions about social issues, access to public services in terms of homelessness: Again, for high school students, I wonder if the concept of social Darwinism ties into curriculum outside the sciences. There are great readings and from there conversations that can be had about the idea of applying biological concepts to humans. A sensitive topic no doubt, but one that many high schoolers may be willing to approach.
3. Discussions about our responsiblity to respond to global climate change: Gobal climate change is an important topic that should be discussed. As plants begin to shift their life cycles according to changes in climate, animals will (and have begun to) respond to these changes. It might be interesting to have students consider what changes might occur in the animal world as ecosystems begin to shift. Can evolution occur fast enough for all animals to adapt to the changes? How might natural selection act on animal coloration, behavior and physiology?
Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.
Videos and photographs:
