Qualitative Data
On the light-coloured “tree bark” the predator often captured the moths that were closer in distance and of the melanic moths that did not camouflage well with the background. As the experiment progressed, there were more light-coloured moths than melanic moths.
On the dark-coloured “tree bark” the predator also captured the moths that were closer in distance but more of the light-coloured moths. After five trials, there were more melanic moths and light-coloured moths. With the intermediate-coloured “tree bark” the closest moth to the predator were also captured. The different colours of moths were equally captured with a bit more on the melanic moth side.
Data Processing
Overview
I have chosen to use the format of tables to display the data of the percentages of melanic and light-coloured moths left after each trial/generation on different coloured “tree bark”. I have chosen the format of tables because it provides a clear understanding of the collected data and because they are one of the most useful and simple way of data presentation. I have chose to use a line graph to compare the results because it is the best way to visually show the relationship between melanic and light-coloured moths on different coloured “tree bark”
Sample Calculations
Average
Average = Sum of observations
Number of observations
43.3 + 36.7 + 40.0 + 40.0 + 40.0 + 40.0
5
= 40.0
Standard Deviation
Formula:
∑(x-m)2
n-1
∑x = 23.8
n=5
∑(x-m) = 0
(n-1) = 4
∑(x-m)2= 21.7
SD2 = 21.7/4
= 5.43
SD = 2.33
T-Test
Formula:
t= X1-X2
√( (N1-1)S21+(N2-1)S22)/ (N1+N2-2(1/N1+1/N2 )
X1 = Mean in Sample 1
X2 = Mean in Sample 2
N1 = # in Sample 1
N2 = # in Sample 2
S21 = Variance in Sample 1
S22 = Variance in Sample 2
t= 88.0-51.3
√( 5-1)(70.1) + (5-1)(53.3))/((5+5-2)(1/5 + 1/5))
= 36.7
√( (280.2+213.2)/(8)(2/5)
= 36.7
√(493.4)/(16/5)
= 36.7
√( 154.2)
=36.7
12.4
t value= 2.96
Presentation
Graph 1. Comparing the percentage of melanic and light-coloured moth population remained after 5 trials/generation of a predator’s hunting on light-coloured tree bark.
Graph 1. Comparing the percentage of melanic and light-coloured moth population remained after 5 trials/generation of a predator’s hunting on intermediate-coloured tree bark.
Graph 1. Comparing the percentage of melanic and light-coloured moth population remained after 5 trials/generation of a predator’s hunting on dark-coloured tree bark.
Processed Table 1. Calculations of the percentages of light-coloured moths and melanic moths left on light-coloured “tree bark”.
Processed Table 2. Calculations of the percentages of light-coloured moths and melanic moths left on light-coloured “tree bark”.
Processed Table 3. Calculations of the percentages of light-coloured moths and melanic moths left on light-coloured “tree bark”.
Processed Table 4. Calculations of the percentages of light-coloured moths and melanic moths left on light-coloured “tree bark”.
Processed Table 5. Calculations of the percentages of light-coloured moths and melanic moths left on light-coloured “tree bark”.
Processed Table 6. Calculations of the percentages of light-coloured moths and melanic moths left on intermediate-coloured “tree bark”.
Processed Table 7. Calculations of the percentages of light-coloured moths and melanic moths left on intermediate-coloured “tree bark”.
Processed Table 8. Calculations of the percentages of light-coloured moths and melanic moths left on intermediate-coloured “tree bark”.
Processed Table 9. Calculations of the percentages of light-coloured moths and melanic moths left on intermediate-coloured “tree bark”.
Processed Table10. Calculations of the percentages of light-coloured moths and melanic moths left on intermediate-coloured “tree bark”.
Processed Table 11. Calculations of the percentages of light-coloured moths and melanic moths left on dark-coloured “tree bark”.
Processed Table 12. Calculations of the percentages of light-coloured moths and melanic moths left on dark-coloured “tree bark”.
Processed Table 13. Calculations of the percentages of light-coloured moths and melanic moths left on dark-coloured “tree bark”.
Processed Table 14. Calculations of the percentages of light-coloured moths and melanic moths left on dark-coloured “tree bark”.
Processed Table 15. Calculations of the percentages of light-coloured moths and melanic moths left on dark-coloured “tree bark”.
Processed Table 16. Mean and standard deviation of light-coloured “tree bark”
Processed Table 17. Mean and standard deviation of intermediate-coloured “tree bark”
Processed Table 18. Mean and standard deviation of dark-coloured “tree bark”
Processed Table 19. Mean, standard deviation and T test of Melanic Moths on intermediate-coloured “tree bark” and dark-coloured “tree bark”
*From this data, the T test of the results of the experiment is in the critical region and the results are therefore significant.
Conclusion
The results support the hypothesis that the appearance of individuals will influence their likelihood of being seen and eaten by predators. Using the light-coloured “tree bark”, the predator captured more of the melanic moths than the light-coloured moths. After switching the moths captured to the opposite colour to put back on the “tree bark” for 5 trials which in this case represents generations, mostly light-coloured moths remained. With the dark-coloured “tree bark” more of the light-coloured moths were captured resulting in more melanic moths remaining on the “tree bark”. With the intermediate-coloured “tree bark” the number of melanic and light-coloured moth were approximately equal with some fluctuations in the 5 trials. The melanic moths will have a higher success of surviving on dark-coloured environments. The light-coloured moths will have a higher success of surviving in light-coloured environments. It is because of their ability to camouflage in those habits from predators. There were more melanic moths on dark-coloured “tree bark” and more light-coloured moths on light-coloured “tree bark” because of their ability to camouflage in those habits and therefore have higher survival rates from predators. As the opposite colour of moth from its habit dies off, natural selection will favour the moths that can camouflage to its surroundings. In the 50 years after the Industrial Revolution, the melanic moths went from making up just 2% of the population to making up over 85%, a change that could only be explained by natural selection and industrial melanism. Genetic drift would be far too slow a process to account for this. This experiment clearly shows the evolution by natural selection in response to its environmental change. The theory of Natural Selection was proposed by Darwin and Wallace. Species of moths showed inherited variation. There is usually an overproduction of offspring so it led to the moths struggle for survival. As the Industrial Revolution progressed, soot and smoke started to build up on trees and lichens (moth habitat). The melanic species of moths are better adapted than the light-coloured moths because of their ability to camouflage with the darken trees and lichen. This ability made them less likely to be seen and captured by predators. The light-coloured moths that are less able to adapt got captured by predators and the population started to decrease. However, the better adapted melanic moths reproduced and passed on its characteristics due to meiosis and changed the gene frequency. After many generations, evolution gradually started to occur.
Limitations and Evaluation
There were a few limitations to the experiment such as the timer not yelling “hunt” simultaneously as they started the stopwatch and not yelling “stop” at exactly four seconds. This would alter a control in the experiment could cause the predator to either capture less or more moths. There could also be limitations due to the eye sight of predators. Some predators took off correction glasses, put on correction glasses, wore sunglasses or used regular vision. We were all in generally in a dark environment trying to blur our sight. However, we do not know that the real predators of moths have unclear vision or they are nocturnal and hunt when it is dark the sun sets. They could have a clearer or worse sight than could we had while hunting. This is turn causes us to be inaccurate when trying to simulate the hunting environment and sight of the predators and alters the results. In addition the closeness of the predator to the moths might have been close than an arm’s length away and therefore will result in the predator catching more moths. Another error could be randomness of placing the moths on the “tree bark”. Sometimes the same colour moths were close together and thus gave an advantage to the predator to catch all the moths of that colour. The predator also usually captured the moths not due to colour but proximity. They picked up whichever colour of moths that were close to them in length instead of the ones that instantly caught their eyes. This would entirely alter the results of the experiment. The different shade of the intermediate colour tree bark and light-coloured moths for each group could change the results of the experiments containing those variables because then the colour would not a control and would change the results. All the limitations would cause the result of the percentages of melanic and light-coloured moths on different colour “tree bark” left after hunting to be inaccurate. Although there are limitations, the T-test done for the experiment comparing the melanic moths of intermediate-coloured and the dark-coloured “tree bark” gave a t value of 2.96. Using the significant value of 0.05 for a two-tailed experiment, and 8 as the degree of freedom, the critical number is 2.31. Since the t value is greater than 2.31 we can conclude that the results of this experiment are indeed significant.
Improvements that could be made to this experiment to make it of a more accurate simulation include researching moth predators. Finding out if they are nocturnal or diurnal and details of their eyesight could be helpful when trying to simulate the environment and every group should have the same conditions. The same person should also be kept as the predator to keep that as a control. Since every person has different speeds and ability to pick up the moths, keeping that person the same would be helpful to establish as a control for a more accurate result. In addition, because humans have opposable thumbs, it is much easier for us to pick up paper then for predators to capture their prey. Perhaps limiting our finger use during the experiment could result in a more precise simulation. Furthermore, an improvement could be made by taping the “tree barks” on a vertical surface such as a wall and capturing moths were are taped to the “tree bark” to simulate moths on a tree. To time the four seconds more correctly could be possible by using a kitchen timer to count down 4 seconds so the predator could stop when the timer beeps. This would eliminate the reaction time for the Timer to yell stop after seeing 4 seconds on the stop watch. Groups should have used the same shade of intermediate-coloured “tree bark” and lighter-coloured moths. This would keep the control of colour constant throughout every group.
Analysis
b) See Processed tables 1-15.
c) See Graphs 1-3.
d) The lighter-coloured moths were most successful in avoiding predation in the pre-industrial Revolution bark habitat because they were able to camouflage with the colour of the bark. As for the post- industrial Revolution, the darker coloured moths were most successful in avoiding predation because they were able to camouflage into the bark.
e) Based on my data, I believe that natural selection did occur in these moth populations because from processed tables 1-15, the comparison of the percentages shows that the better adapted moths had an increase in population while the least adapted moths had a decrease. Depending on colour of the habitat they were in, the moths that were able to camouflage and blend in with the tree bark is known to be the fittest one because their chance of survival is higher. As the genes of the weaker moths get eliminated, the gene of the fittest ones increases after every generation by meiosis.
Evaluation
f) The purpose of using an intermediate-coloured background in this investigation is for it to represent a control. With a neutral coloured tree bark we can then clearly see that there is a significant difference when using a light and dark-coloured tree bark in terms of the percent of moth left after five generations.
g) See Limitations and Evaluation
h) See Limitations and Evaluation
Synthesis
i) Some poisonous frogs have vivid colours to warn their predators that they are toxic. They do not blend into their surroundings because if they did, they cannot warn their predators. Poisonous frogs and usually very small compared to their predators. If they did blend, they still have the chance of getting captured. However, if they are bright and vivid, they have a better ability to survive by scaring away predators. Through natural selection, the poisonous bright coloured frog probably adapted better than the one that blended into its surroundings. Because of evolution, most poisonous frogs have striking-colouration.
j) Lamarck believed in the evolution theory of use and disuse. In the example of the giraffe, he believed that a given giraffe could, over a lifetime of straining to reach high branches, develop an elongated neck. This theory does not support the peppered moth example because a moth could not adapt to its surroundings by changing its characteristics through the theory of use and disuse.
k) If the original population of the peppered moth did not show variation and evolution did not take place, the moth would slowly die off because of their clear visibility to potential predators. The species could completely become extinct or they would move and find a new environment to live where it hasn’t been affect by industrial melanism.
l) Industrial melanism means the darkness of the skin, feathers, or fur obtained by a population of animals living in an industrial region where the environment is soot and smoke darkened.
m) Biologist Laurence Cook’s new founds supports Kettlewell’s hypothesis to an extent because it says the lighter-coloured moths are making a dramatic comeback when the tree barks are becoming lighter again. The light-coloured moths are now more able to adapt in a lighter-coloured tree bark and the population is increasing because of natural selection. In this case it supports Kettlewell’s hypothesis because he suggested that the colouration of the peppered moth was a result of changes in the environment. On the other hand, it does not support Kettlewell’s hypothesis because Laurence stated that the moths were seldom seen on trees, which means that the moths did they also live there even though the tree barks favours them. Kettlewell’s premise of testing the likelihood of moth’s appearance influencing natural selection only on tree barks was incorrect.
WORKS CITED
Shuttleworth, Martyn. "Industrial Melanism - How Human Contamination Evolved the Peppered Moth."The Scientific Method. Web. 24 Oct. 2009. <http://www.experimentresources.com
/industrial-melanism.html>.
Shuttleworth, Martyn. "Industrial Melanism - How Human Contamination Evolved the Peppered Moth."The Scientific Method. Web. 24 Oct. 2009. <http://www.experimentresources.com
/industrial-melanism.html>.