An Investigation into a Woodlice's Preferred Choice of Environment.
AN INVESTIGATION INTO A WOODLICE'S PREFERRED CHOICE OF ENVIRONMENT.
SCENARIO
When he was gardening, Kevin noticed that he rarely ever saw woodlice, but when he lifted stones or wood etc. The woodlice found underneath seemed to run in all directions.
HYPOTHESIS
Woodlice prefer dark, damp and warm surroundings to light, dry and cold environments, by setting up a choice chamber with all of the available conditions within, I will determine that woodlice do prefer a wetter, darker environment to a lighter, drier one. And I predict that you will find that the woodlice mover quickly to the wet/dark compartment, more so than the other three.
Null Hypothesis:- Woodlice do not have a preferred environment for living in. Any difference that occurs will be due to chance factors.
BIOLOGICAL KNOWLEDGE
Woodlice appear as insects but in fact they are crustaceans. They are one of the only crustaceans known that have adapted to living on land instead of water. Like other insects, they have no shell, and they possess no waxy cuticle, which helps prevent water conservation. Because of this, woodlice are prone to losing water easily via evaporation due to their outer skin being very permeable. This is why they prefer to remain in damp environments. It is said that in dry air, within two hours they will be dead, (www.science.org.uk).
By observing them in different environments (e.g. light/dark, wet/dry), a significant difference in their behaviour and reaction should be seen. Woodlice tend to move quicker in dry places than damp places. You may also see them 'clump' together. This helps them to reduce their water loss as it reduces the surface area that is in the open air, as by less air passing their outer layer, less water is lost in that way. This is the same as when some plants that may have adapted to hotter climates have sunken stomata. This serves the same purpose.
Woodlice lack the waxy cuticle that many insects and also plants have to reduce water loss by evaporation, this makes them very different from them. this is why woodlice are very dependent on the conservation of their moisture.
When exposed to light, woodlice are said to be negatively phototaxis, a reason for this could be the heat element that is associated with light. If a mammal encounters a lot of heat, it will produce sweat to cool its body down. This causes the amount of water conserved in their bodies to reduce. The same will occur in a woodlouse and therefore they will lose some water, water which is vital for them to survive, because of this, woodlice will attempt to move away from the light into more darker regions, where they hope it will also be cooler.
It says that when exposed to different temperatures, woodlice will exhibit a non directional response - orthokinesis (speed of movement). Meaning that when exposed to higher or even lower temperatures than they prefer, woodlice will move, attempting to find a more suitable environment.
Woodlice will also exhibit a noticeable response when exposed to a different humidity level. They will move with increased speed (orthokinesis), and with a decrease in the rate of turning also, (klinokinesis) in dry conditions, and moving at a slower rate of movement in more humid conditions. Thus, resulting in the woodlice accumulating in more humid regions.
Another effecter on a woodlouse's movement is whether or not their body surface is in contact with any other object (including other woodlice). They exhibit a positive thigmokinesis when this occurs, and will move around so that the maximum amount of their body is touching something else, whether it be a rock or another woodlice. This results in the woodlice forming clumps. By doing this, it reduces the amount of water lost by diffusion of their outer shell. The woodlice in the middle consequently lose less water than those on the outside, and therefore after some time they will all switch places to ensure that they are all conserving as much water as is possible.
It can be said then, that woodlice have a preference for dark, damp, fairly warm surroundings. This is true as woodlice tend to be found under rocks, stones and wood. It is clearly dark and damp underneath these, and would also be fairly warm as heat cannot be lost easily as wind may not pass easily underneath the wood etc, making it cooler.
INTRODUCTION
This experiment is to test the preferred environments of woodlice. As is said above, it is said that woodlice prefer fairly dark and damp environments to live in as compared to drier ...
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It can be said then, that woodlice have a preference for dark, damp, fairly warm surroundings. This is true as woodlice tend to be found under rocks, stones and wood. It is clearly dark and damp underneath these, and would also be fairly warm as heat cannot be lost easily as wind may not pass easily underneath the wood etc, making it cooler.
INTRODUCTION
This experiment is to test the preferred environments of woodlice. As is said above, it is said that woodlice prefer fairly dark and damp environments to live in as compared to drier and lighter ones. By using a choice chamber combining these four different conditions, and by using cotton wool, silica gel, a lamp and some black paper I will be able to see if there is a difference in the condition that is picked the most by a woodlouse. In order to make sure the experiment doesn't encounter any difficulties, I am going to ensure that the woodlice are kept out of harm for the whole time. Giving them plenty of time so that they do not lose too much water, water that is vital to them to survive in this world as has already been said in the biological knowledge.
In this experiment I am experimenting with the woodlice by placing them in different situations prior to being placed in the choice chamber. 10 will be placed in a dry container, 10 in a wet container and 10 in the conditions in which the woodlice were living prior to the experiment. By doing this I will interpret the movements given by the different groups once placed in the choice chamber. I will need to mark the woodlice in order to do this. I have chosen to put a small white dot on the back of the normal woodlice and two dots on the backs of those placed in the dry conditions.
By doing this I will be able to differentiate between the woodlice and therefore know if their movements are quicker than their counterparts due to the environment they were placed in prior to the experiment. In order to test the significance of my results, I will use a statistical test. The one I have chosen is the chi-square test. I have chosen this particular test as I have quantitative data and so will be able to conduct this test with ease. Once I have calculated the test, an overall result will enable me, by looking at a table about the significance of statistical tests and by calculating the number of degrees of freedom, I will be able to say whether or not my experiment has worked. And, if so, exactly how significant it is.
INDEPENDENT VARIABLE
> Woodlice tested under four conditions: wet/dark; wet/light; dry/dark; dry/light - this will be achieved by using a choice chamber and by splitting it into four different chambers for each of the conditions involved, by using cotton wool, silica gel and some black paper this should be achieved quite simply.
> Under each of these situations, the safety of the woodlice will be taken into account and every precaution will be taken to ensure they come to no harm - by making sure they are not exposed to overheating which may damage them permanently, and by also ensuring that they have food and shelter before and after the experiment commences.
CONSTANTS
> There will be 10 woodlice in each condition (wet and dry) and 10 will remain in the conditions in which they were living prior to the experiment taking place.
> The light intensity in the light region of the choice chamber (a lamp will be used to achieve this) - we will measure this using a probe that measures light intensity and note it in the results.
> The darkness of the dark region - this will also be tested using the light intensity probe to ensure it is accurate.
DEPENDENT VARIABLE
As soon as the woodlice are all let into the choice chamber I will begin timing. Then I will watch the clock and the woodlice and every 30 seconds for 10 minutes I will note how many woodlice are under each condition. This will determine which environment the woodlice favour. There may be some woodlice that don't move completely into another section though. If they are half and half I will simply note this at the time, also noting between which conditions they are. I will also take any woodlice that is three quarters of the way into a condition as part of that condition.
APPARATUS
> 60 woodlice - 30 for each experiment (the experiment is being conducted twice)
> Choice chamber - split into four sections, dry-dark, wet-dark, dry-light, wet-light.
> Cotton Wool - to be dampened with a little water for the damp section of the choice chamber.
> Silica Gel - to put underneath the muslin in the dry section of the choice chamber, it will ensure that all moisture is absorbed by it and not by the woodlice.
> two identical containers, one for the damp scenario and one for the dry scenario that some woodlice will be placed in via to the experiment.
METHOD
. 10 woodlice will be placed in dry conditions in a container for ten minutes - this will be achieved by placing silica gel underneath some muslin before introducing the woodlice to the container
2. Another 10 woodlice will be placed in wet conditions in a container for 10 minutes - this will be achieved by placing some damp cotton wool/tissue underneath some muslin before introducing the woodlice to the container.
3. Another 10 will be drawn from the other container containing all the woodlice. (Meanwhile the other 30 will remain in the container with things from their natural habitat with leaves, rocks and food.)
4. Whilst the woodlice are in their different conditions, I will begin preparing the choice chamber for each condition by placing damp cotton wool into one half of the choice chamber, and into the other half, I will place some silica gel.
5. Muslin will then be placed all over the choice chamber to ensure the woodlice aren't walking on the cotton wool or the silica gel so they don't experience any discomfort whatsoever.
6. I will then put black paper over half of the choice chamber, this will be the dark region. It will have to ensured that the black paper covers a quarter of the cotton wool and a quarter of the silica gel. All four conditions are now set. (see appendix 1)
7. Once the woodlice have been in there different conditions for the ten minutes, I will move the woodlice from their separate containers 10 out of each condition into the choice chamber. They are inserted directly in the middle of the four conditions. Once they are in I will commence timing. At every 30 seconds I will count the wood lice to see how many are in each condition, until ten minutes of timing has passed. These results will be noted in the table of results (see appendix 2).
SAFETY ASPECTS
> A lab coat will be worn
> Safety glasses will be worn
> Gloves will be worn
> The woodlice will be monitored very carefully throughout the experiment very carefully. If at all during the experiment they seem to be suffering discomfort, the experiment will be stopped and the woodlice returned to their natural habitat.
Appendix 1
As you can see the choice chamber has been split into four different sections. Sections 1 and 2 have cotton wool underneath them, whilst sections 3 and 4 have silica gel underneath them. Sections 2 and 4 also have black paper over the top of them, stopping any light form getting in.
This mean that:-
Section 1 - wet/light
Section 2 - wet/dark
Section 3 - dry/light
Section 4 - dry/dark
The woodlice will be placed in the whole in the middle of the chamber, from here they can access all four conditions easily and it makes the experiment more valid as each condition is the same distance away from them.
Appendix 2
Amount of
time passed
wet/dark condition
wet/light condition
dry/dark condition
dry/light condition
other notifications noticed
from the woodlice
30s
60s (1)
90s
20s (2)
50s
80s (3)
210s
240s (4)
270s
300s (5)
330s
360s (6)
390s
420s (7)
450s
480s (8)
510s
540s (9)
570s
600s (10)
CHI-SQUARE
In order to test the significance of my results, I will carry out a statistical test on my data that will enable me to determine their validity. The chi square test is a test of association used on independent data at a nominal level (Cardwell 2002). By using the formula:
?2=? (O-E)2/E
Where O stands for the observed results obtained, and E is the expected results. Chi-square uses the observed result I have recorded with the results that would be required in order for my null hypothesis to be retained. Seeing as I expected there to be no difference n where the woodlice would go, my expected number is 10, meaning that there would 10 in each condition at all times. In order to get the observed for each condition, I worked out the overall average and am using that in my test.
Here is a table for the result of my chi-square test:
CONDITION
O
E
(O-E)
(O-E) 2
(O-E)2/E
dark/wet
7.3
0
7.3
53.29
5.329
light/dry
2.7
0
-7.3
53.29
5.329
light/wet
8.925
0
-1.075
.155625
0.155625
dark/dry
1.075
0
.075
.155625
0.155625
? (O-E)2/E = 10.96925
As I have four degrees of freedom (four fields of results), I can now look at a statistical table to see how significant my result is. By looking in the table by 4 degrees of freedom and under the column for the probability being less than 0.05 would have to be below the critical value of 9.49. As my result (10.96925) is above this number, then the probability that my results occurred due to chance factors is very slim indeed. This would mean that my null hypothesis: - "Woodlice do not have a preferred environment for living in. Any difference that occurs will be due to chance factors" would be rejected, and my hypothesis retained. This does not mean, however that other factors did not affect the woodlice's behaviour when in the choice chamber. Other factors also come into play. The woodlice may have been under stress due to the experiment they were under, or they may have been lost due to the fact that they had been taken from their natural environment without knowledge.
RESULTS
After doing each experiment twice, I calculated the average for both and put all of them, every condition into the table that follows.
TIME PASSED
LIGHT/WET
DARK/DRY
LIGHT/DRY
DARK/WET
30s
7
23
8
32
60s (1 min)
4
26
7
33
90s
2
28
4
36
20s (2 mins)
6
24
8
32
50s
7
23
0
30
80s (3 mins)
7
23
5
35
210s
20
20
9
31
240s (4 mins)
7
23
6
34
270s
21
9
6
34
300s (5 mins)
9
21
6
34
330s
5
25
4
36
360s (6 mins)
7
23
5
35
390s
7
23
4
36
420s (7 mins)
9
21
2
38
450s
24
6
4
36
480s (8 mins)
20
20
39
510s
8
22
6
34
540s (9 mins)
6
24
4
36
570s
23
7
4
36
600s (10 mins)
8
22
5
35
I also plotted these results in a graph. You can see the results for this in the line graph below. This can then be used for comparison between each condition.
By looking at the graph you can see that the Dark/Wet section had the most woodlice in it. This would support the hypothesis that they prefer this kind of environment. The woodlice also seemed to like the Dark/Dry and Light/Wet conditions. This could be due to the fact that they have some of the features that woodlice seem to like.
INTERPRETATION
By looking at my graphs I have noticed a pattern on some of them. In the conditions of light/wet and dark/dry, you can see that the lines cross each other a fair bit, and therefore means the woodlice are moving to and fro quite a lot. If you compare this with the graphs for light/dry and dark/wet you can see that the majority of the woodlice are in the dark/wet environment, thus supporting my hypothesis that woodlice prefer a more dark and damp environment.
EVALUATION
As you can see, I had to amend my experiment, as I had not taken everything into account.
After setting up most of my apparatus and collecting in my woodlice, and putting them in their appropriate container, I realised that it was going to be impossible to see into the dark region to see if they were in the dark/wet region, or the dark/dry region. Therefore I decided to change my experiment slightly to determine whether or not woodlice preferred a light/wet, light/dry, dark/wet or a dark/dry environment. I am still testing the same variables as mentioned previously in my plan, but not all at once.
In order to do this I changed the way in which I set up the choice chamber.
I split it into two different sections, and placed damp cotton wool in one and left the other one as it was. I then put black card over one side of the lid of the choice chamber, and by putting muslin in between the bottom and the lid I ensured that no woodlice would touch the cotton wool or the empty section. As I was doing this I made sure that the first time I conducted it that the entire black half of the lid was placed over the dry section of the choice chamber. I then put a lamp over the choice chamber and put in twenty woodlice. By counting how many woodlice were visible in the light section of the choice chamber I could then deduct this number from 20 to work out how many were in the dark section. I counted this every 30 seconds for 10 minutes as I had planned to do before. I then repeated this again using another 20 woodlice and placed the other 20 into a container containing things from their natural habitat and some damp cotton wool at the bottom. I did the same thing again with the next twenty and recorded the results in the tables you have just seen in the results section. I then took all the woodlice out and placed them another container with dampness and soil.
I then had to change the choice chamber around. By placing the lid back on with the damp cotton wool section underneath the dark region of the chamber. I then used the woodlice that I had used first before and placed them in their and timed and counted again, and then repeated it again but using the woodlice from the second container.
This way proved to be a lot more efficient in counting the woodlice. They did seem to clump a lot thought, in all conditions. Thus proving that they do clump to conserve water as was said in the biological knowledge. They also showed a thigmokinesis, they always ensured that they were against something. On occasions it was other woodlice, but in the results where you can see that one woodlouse was on its own at some point it was always up against the edge of the choice chamber.
I would therefore say that my experiment had not been a success as the chi-square test proves. Perhaps in order to change it, I would attempt to use a bigger choice chamber, with more woodlice and I would try to change conditions more, and possibly introduce wind into it also.
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