Download Name: Evolution and Adaptation: Wooly Worms Simulating Natural

Name:
Evolution and Adaptation: Wooly Worms Simulating Natural Selection
NGSSS: SC.912.L.15.13 Describe the conditions required for natural selection,
including: overproduction of offspring, inherited variation, and the struggle to survive,
which result in differential reproductive success.
Purpose: By completing this lab, you will become familiar with specific adaptations
such as coloration and how this can ultimately determine what species dominates a
population.
Background Information:
Wooly worms are simply pieces of yarn distributed in a random manner over a
designated area of the school yard. You are going to simulate the feeding of predators
that prefer the wooly worms in their diet. You and a partner will feed on (collect) as
many of these delectable organisms as possible in a timed session. The collected worms
will be counted and recorded and then we will use a Chi-Square test to determine if the
worms were collected in a random process or by some sort of selection process.
Since worms of certain colors are best suited to survive in their environment, certain
variations are more favorable to the individual and species than others. These favorable
variations are termed adaptations. Adaptations increase an organism’s chances of
survival and subsequent ability to reproduce and pass on its traits (favorable genes) to its
offspring. An example of adaptation is cryptic coloration, whereby an organism blends
into its environment so well that it is difficult to detect. Cryptic coloration can help
animals escape predators or capture unsuspecting prey. This “survival of the fittest”
concept is supported by Darwin’s Theory of Natural Selection.
As with many other worms, the wooly worms in this activity represent or simulate insect
larvae in a natural habitat. They will complete their metamorphoses into adult insects, so
long as they survive. Predation places a selection pressure on certain colors of wooly
worms; those who exhibit favorable adaptations are positively selected for. Those who
may contrast with their surrounding s are easy prey for the predatory birds, and are said
to be selected against. The gene frequencies for wooly worm coloration will changesuch changes illustrate the dynamics of natural selection. Drastic and sudden changes in
the environment may lead to extinction, but this is not common in nature.
Random Numbers and Selection:
The different colors of yarn distributed randomly on school grounds represent the
different color varieties of wooly worms. If these yarn pieces are collected randomly, the
number of worms of each color should be nearly equal. If, however, the data does not
support this hypothesis, then selection of certain colors must have occurred. A null
hypothesis is proposed for these circumstances, something to the effect that the color of
the wooly worms will have no effect on numbers of each color collected. If you can
reasonably show that this is not the case through a statistical process, then the selection
must have occurred. The Chi-Square test will be used to the test the null hypothesis by
comparing the expected number of worms of each color against the observed numbers
actually collected. A variance between the expected and the observed numbers is likely
in any chance event. The Chi-Square test will determine if this variance is within
acceptable statistical limits to support the original null hypothesis. The Chi-Square test
will reveal how likely it is that the worms were collected randomly.
Null hypothesis: Remember that we cannot prove hypotheses in science – we
can only support hypotheses with repeated experiments. However, we can
disprove hypotheses with data.
So professional researchers create a null hypothesis that predicts no significant
change in the data. This is typically the opposite of what researchers want to
show – scientists try to obtain data that does show a significant change. If they
do, then they reject their null hypothesis, and therefore indirectly support their
true hypothesis.
Example: Medical researchers are trying to show that the new drug X
works better than aspirin at curing headaches.
Hypothesis: New drug X works better than aspirin.
Null hypothesis: New drug X works just as well as aspirin.
Data:
% of people stating
headache disappeared
How well headache medicines work
100
80
60
Series1
40
20
0
Drug X
Aspirin
Brand of medicine (100 mg)
Conclusion: Bar graph clearly shows drug X working better than aspirin.
Null hypothesis is rejected, and therefore original hypothesis is supported
(though not proven).
Materials:
14 colors of yarn
Master chart of yarn color
Chi Square Probability Table
Chi Square Calculations Table
Calculator
Procedure:
Before activity:
1.
After you understand the activity, develop your hypothesis and the null
hypothesis.
2.
Divide into pairs, you are now a “hunting pair”
During activity:
3.
Collect as many worms as you can in two minutes.
4.
Return to the lab and determine the numbers of each worm collected.
After Activity:
5.
Collect class data and work on Chi Square Data Table. The number of each
worm collected should be placed in the first column- “Observed.”
Data:
Hypothesis: Make a prediction about how coloration will affect which worms will
be eaten and which worms will survive.
_______________________________________________________________
________________________________________________________________.
Null Hypothesis:
________________________________________________________________________
Color
A. Observed
B. Expected
C.
Obs.- Exp.
D.
E.
(Obs-Exp)2 (obs.-Exp.)2/ Exp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Total =X2 =
1. Fill in the Chi-square table using the following:
A. Class Observed Data
B. The “expected number” for each color is determined with your calculator by dividing the total
number observed by the number of different colors:
Total number observed
Number of different colors
= Expected number for each number
C. Subtract the expected number from the observed number. Answer may be either positive or
negative.
D. Square the number obtained immediately above. (Negative numbers will now be positive).
E. Divide the answer immediately above by the expected Exp number.
Repeat the calculations for each of the colors observed during the feeding period.
Determine the Chi-square value based on the following equation:
Χ2 = ∑
(observed - expected)2
expected
Add up all the final figures (column E) for each color to get the sum of Chi-square.
2. Determine the degrees of freedom to be used. The degrees of freedom to use will always
be one less than the total events (colors) observed. For example, if 14 colors were
observed, then 13 degrees of freedom will be used.
3. Determine the probability that the Chi-square value you obtained is caused by chance
factors or by selection. The columns with the decimals - .99, .95, .50, .01, and .001 refer
to probability levels of the Chi-square numbers illustrated. If you obtained a Chi-square
value of 9.93, then you could conclude that the observed numbers you obtained did vary
from the expected but such a variance is likely 50% of the time. Therefore, chance alone
could cause such a variance. The null hypothesis would be supported. However, if a Chisquare value of 22.36 or higher was obtained (at or below the .05 level or probability),
then we would have to conclude that chance factors are not likely to cause the variance
observed. The null hypothesis would be rejected. Selection of certain colors over others
must have occurred.
Analysis Questions:
1)
Should we accept or reject our null hypothesis? Why?
2)
Which colors of worms were subjected to appositive selection pressure? How
about a negative selection pressure? Explain.
3)
Thinking about the last question, how would you expect the selection of
certain worms to change with both the time of day and season? Thin about
feeding times, ability to see color, vision acuity, etc. in answering this
question.
4)
Consider the environment in which you fed like crazy on the poor wooly
worm. If this environment remained unchanged for many years, how would
gene frequency be affected in future generations?
5)
Suppose there was an increase in rain on the grounds, how would this affect
the gene frequency of the different colors of the wooly worm population in the
future?
6)
Suppose there was a sharp decrease in rain on the grounds, how would this
affect the gene frequency of the different colors of the wooly worm population
in the future?
7)
Explain the connection between Darwin’s Theory of Natural Selection and
gene frequencies.
8)
While some of the wooly worms blend in with their environment to increase
their ability to survive, some animals actually contrast sharply with their
environment to survive. Why would an animal do this, in other words, can
you think of an organism that does this and how it helps them survive?
Grading List:
Background Information for Activity:
10 points
______
Brief Procedure:
Activity Itself (collecting procedure)
10 points
______
10 points
______
Chi Square Data Table is Completed Accurately:
20 points
______
Analysis Questions are Answered and Fully Explained:
40 points
______
Statistics
Brief Mention of Validity (how could the experiment have been improved?):
10 points
______
Total Points: ______