This investigation looked to see whether the height on the shore would affect the size or aperture size of Gibula Umbilicalis. Gibula Umbilicalis are a species of topshell which live on the rocky shore, they can be found in the
'Investigating the Affect of the Height on the Rocky Shore on the Ratio Length to Aperture of Gibula Umbilicalis Topshells'
Title of Investigation: THE AFFECT OF THE HEIGHT ON THE ROCKY SHORE ON THE RATIO LENGTH TO APERTURE OF GIBULA UMBILICALIS TOPSHELLS
This investigation looked to see whether the height on the shore would affect the size or aperture size of Gibula Umbilicalis. Gibula Umbilicalis are a species of topshell which live on the rocky shore, they can be found in the upper, middle or lower shore and surely must have adapted to live in the upper and middle shore where living conditions are harsher, due to there being less time when the shore is covered by water. As marine creatures they require water to respire, so how do they cope during the time they are out in the air? A preliminary experiment was carried out to choose which heights on the shore would be best to carry out the investigation. A transect with height intervals was used and a count made of the Gibula Umbilicalis at different heights. The two furthest points (i.e highest and lowest) where there was a supply of Gibula Umbilicalis were chosen. A continuous horizontal transect was carried out at these heights and the lengths and aperture size recorded of the topshells found. For each topshell a ratio was made dividing length by aperture diameter. Then a t-test was performed on the two sets of results and showed there was a significant difference between the ratios of the ones in the middle shore and the lower shore. The ones from the middle shore had relatively larger lengths and smaller apertures. From the results it was concluded that the Gibula Umbilicalis in the middle shore had adapted to hold more water, by having a larger shell and lose less of it through the smaller aperture.
Contents
Rationale
Planning
- Hypothesis
- Variables
- Equipment
- Procedure
- Risk assessment
- Preliminary experiment
Implementing
- Choosing heights
- Running mean
Observing and recording
- Results
- Anomalies
Interpreting and evaluating
- Data Processing (t-test)
- Biological principles
- Limitations
Rationale
The rocky shore is full of life with marine creatures and plants that have to adapt to survive harsh conditions and competition. Snails are numerous in number and variation. They have a strong foot muscle which helps them to cling tightly to rocks. This is a useful feature for a creature on the rocky shore as sometimes conditions can be rough, strong waves have great force behind them. However the conditions are subject to change on the rocky shore and some are just as hard on life forms as rough tidal action, for example when the tide goes out organisms that require water will have to do without until the tide comes back in and at points on the shore and times of year this can be a very long time indeed. Snails that require water for living have to adapt to survive for long periods of time without a water supply. The lower shore will be without water for a shorter time than the upper shore, it is easier for species to exist here because of that, but this draws in competition for other things, like food. The upper shore has less competition but species that inhabit this area must adapt to be able to exist without being under water for longer times than they would be in the lower shore. Gibbula umbilicalis is a a topshell snail, they are found across the shore, upper to lower. It would be expected that there is a difference between the Gibbula umbilicalis in the lower shore and the Gibbula umbilicalis in the upper shore. To investigate whether or not this is correct the ratio between the length of the shell and the aperture of the snails could be measured for snails in the upper and lower shores. Gibbula Umbilicalis are a good choice for this investigation as they are easy to find and identify due to their characteristic grey-green shell with purple zigzag pattern, and also the large quantity of them over the rocky shore.
Planning
Hypothesis
I think there will a significant difference in the ratio of topshell length and aperture size between the Gibbula Umbilicalis on the upper shore and the lower shore.
Variables
My independent variable will be the height on the shore. I will carry out a horizontal continuous transect at two heights on the shore, which I will record. I will use my preliminary experiment to decide these heights.
My dependent variable will be the length of the topshell, and the size of it's aperture. I will put these into a ratio of Aperture:Length. Due to the shape of the topshell there is no definite length of shell, but I will measure from the same correlating points (see appendix) for each shell, otherwise the results will not reflect correctly the actual data. The aperture is an oval shape, so I will need to set a standard method of measuring this also (see appendix).
The variables I will control will be the following:
* The time at which the results are taken will be the same, as It will take me no longer than several hours to collect enough results. Collecting results on different days could make the investigation unreliable.
* The standard method for measuring the length and aperture will be constant
* The Equipment and accuracy to which the results will be measured will be kept the same throughout the investigation
* I will only take shells from one face of the rock i.e. sea-facing or ...
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The variables I will control will be the following:
* The time at which the results are taken will be the same, as It will take me no longer than several hours to collect enough results. Collecting results on different days could make the investigation unreliable.
* The standard method for measuring the length and aperture will be constant
* The Equipment and accuracy to which the results will be measured will be kept the same throughout the investigation
* I will only take shells from one face of the rock i.e. sea-facing or non sea-facing. The two faces will receive different amounts of light and the conditions will be different, I do not want this to affect my investigation.
* I will not collect Gibula Umbillicalis from rockpools. I think whether the topshells are in or out of a rockpool could affect the size of the topshell and so I want to make sure that it does not change the outcome of my investigation
Equipment
I have chosen equipment for its accuracy and practicability.
I will need a 1/4 m2 quadrat. This will be moved along my continuous horizontal transect as a boundary for my selection area for topshells. I think 1/4 m2 is a suitable area for selection. It were smaller I would have to move a large distance to collect enough topshells to have good results. It would be better to be able to collect most of the topshells from similar areas across the height. If it were larger, the sample would be all from the same area and I want to make sure that the sample is more diverse than this, and I think that 1/4 m2 is the right size to get a good spread of data from a few different similar areas across the same height above the sea.
I will need a calculator. This will help me calculate the ratios. It will speed up the investigation as I wont have to work about the ratios in my head or otherwise manually. As I am planning to record a lot of results speed is a necessity, especially with the motive nature of the tide. Also I can use the random number generator function on my calculator to help choose random starting positions for my continuous transect. This is useful as I need to eliminate any bias in order for the outcome of the investigation to be a true reflection of the actual situation.
I will need a tray. I will put all the topshells I find in the quadrat in the tray. Once I have all of them from the selection area, I will take them out of the tray and measure them. Then I will place them back into the selection area I took them from. This should stop the confusion of measuring the same topshell twice.
I will use vernier callipers to measure the length and aperture size of my topshells. I have chosen this measuring device as it is highly accurate, to a tenth of a millimetre, and I want accurate results. The shells are small and the differences in the size of aperture and length of shell will probably be slight, so I need an accurate measuring tool to pick up little differences.
I will be using a cross-staff (see Appendix). It is a plank of wood, with a spirit level, passing through the middle, perpendicular to the plank, 0.6m from the end. A whole through the plank and an angled mirror allow you to find a point 0.6m above the point on which the cross-staff is resting. This is very useful for moving down the shore at height intervals. I chose to use this piece of equipment because it is a simple fast technique for something that would otherwise be a hard task on the shore. I will need to use it in my preliminary test to find which heights on the shore would be best to perform my investigation at.
Procedure
I will start at a height in the middle to upper shore, chosen depending on the outcome of the results of my preliminary investigation. I will need to make the starting spot random. So wherever I am standing I will generate a random number using my calculator and if it is even my starting position will be to my right, and if it is odd it will be to my right. I will then generate another random number, between 1 and 50 (depending on the width of the shore) and then I will take this number of steps left or right. I will make sure that while taking these steps I stay at a constant height on the shore. I will place my quadrat at my feet. This is where I will start my transect. I will collect all the topshells inside the area of the quadrat and place them in the tray. Once all of them have been collected and placed in the tray I will measure each shell's length and aperture. Then I will place it back within the quadrat. When I have measured all of the shells in the tray I will move the quadrat, horizontally, along the shore. I will repeat the collecting and measuring method. I will record the results into a result sheet, which will have a column for working out a running mean. A running mean is the mean of the recorded results, calculated after each result is taken. First I will have to put in the length and aperture measurements. I will then work out the ratio aperture:length (in 1:X form) by dividing length by aperture. When I have measured 35 topshells from the upper shore my results will be complete. I will then move to my chosen height in the middle to lower shore region. And repeat the method above. I chose to move down the shore, because I will start my investigation in the morning so by the time I have collected my results for the upper shore the tide will be out and it will be safer to walk about the lower shore.
Results
I will make a results sheet to take with me when I head out to the rocky shore to carry out my investigation. Here is a sample of the table I will make up to record my results in:
Result No.
Length
Aperture
Length
Aperture
I will use the t-Test to check whether there is a significant difference between my results. The t-Test is a good choice for this because it uses two sets of results and shows how much the results overlap in relation to the number of results.
Risk assessment
(See appendix for risk scales)
Hazards
Likelihood
Severity
Risk
Rating
Consequent Precautions
Slipping on wet rocks
3
X
2
= 6
Wear appropriate footwear, be careful
Cold winds from sea
3
X
= 3
Wear warm clothing, keep warm,
Problems with sharp acutely angled rocks
2
X
2
= 4
Watch footing while moving across the shore
Carried out to sea
X
4
= 4
Avoid getting too near to the sea.
Attacked by a Crab
X
2
= 2
Be careful not to disturb marine creatures
Preliminary Investigation
I will perform a short investigation before I start my big one to help decide on the best way to perform my main investigation.
I will stand somewhere on the shore and use my calculator to generate a random number, if it is even I will head right or if it is odd I will head left, then I will generate another random number, between 1 and 50 (depending on the width of the shore), and I will take his many steps either right or left. When I stop I will walk to the top of the shore and place my quadrat there. I will then count the number of Gibula Umbilicalis in the quadrat and record the number. I will then use the cross-staff to move down the shore and record the number of the Gibula Umbillicalis in each quadrat. I will then repeat this whole method.
Implementing
I carried out my experiment exactly as I had planned and it was fine nothing had to be changed except I decided to use a running mean.
Choosing heights
Becaue of the results of my preliminary experiment (see Appendix), which were very consistent through the repeat, I managed to choose two good heights on the shore where I could perform my investigation. The results showed normal distribution across the middle and lower shore, but there were none found in the upper shore. I decided to carry out the investigation at the two most different points. I chose height '4' because it was the furthest height up the shore where I had actually found gibbula umbilicalis. I also chose height '10' because it was the lowest height on the shore and I had found gibbula umbilicalis at this height.
Running mean
I realised that deciding a number of topshells to measure was not the best way to get a good result, as I wanted a good average of all the topshells on the shore, and if the ones I found were greatly varied then I would have an average, which would not be accurate. So I decided to use a 'running mean'.
A running mean is an average that you calculate after each recording. So I worked out the ratios and then cumulated and divided them by the number of results every time I took new measurements. Then after I had collected thirty five results I checked the last five to see if their running means were within five percent of the previous one. If they weren't then I would carry on collecting and checking the running mean for consistency. If they were then I would conclude that my results were complete, because they obviously contained values that were very similar.
Observing and recording
Shown below are the results of the investigation into the effects of the height on the shore on the ratio of the gibbula umbilicalis' length to its aperture size.
Results from the upper-middle shore
No.
Length
Aperture
Length /Aperture
cumulative
Running mean
9.4
5.3
.774
.774
.774
2
9.4
5.8
.621
3.394
.697
3
9.7
5.3
.830
5.224
.741
4
0.2
5.5
.855
7.079
.770
5
1.4
6.3
.810
8.889
.778
6
0.0
5.1
.961
0.849
.808
7
1.5
5.4
2.130
2.979
.854
8
0.0
5.5
.818
4.797
.850
9
9.6
5.6
.714
6.511
.835
0
0.5
5.3
.981
8.493
.849
1
1.2
5.3
2.113
20.606
.873
2
8.7
4.3
2.023
22.629
.886
3
9.4
4.8
.958
24.587
.891
4
7.4
5.3
.396
25.984
.856
5
8.7
5.3
.642
27.625
.842
6
8.7
5.0
.740
29.365
.835
7
1.8
6.9
.710
31.075
.828
8
0.0
5.0
2.000
33.075
.838
9
0.3
6.3
.635
34.710
.827
20
9.4
5.2
.808
36.518
.826
21
0.4
5.0
2.080
38.598
.838
22
8.9
5.3
.679
40.277
.831
23
8.8
4.6
.913
42.190
.834
24
7.9
4.0
.975
44.165
.840
25
0.5
5.5
.909
46.074
.843
26
1.5
6.4
.797
47.871
.841
27
1.6
6.1
.902
49.773
.843
28
1.2
6.2
.806
51.579
.842
29
0.7
5.8
.845
53.424
.842
30
0.4
5.8
.793
55.217
.841
31
1.6
6.0
.933
57.150
.844
32
0.7
5.7
.877
59.028
.845
33
1.7
5.9
.983
61.011
.849
34
2.5
6.0
2.083
63.094
.856
35
8.0
4.9
.633
64.727
.849
36
1.2
5.9
.898
66.625
.851
37
2.1
5.9
2.051
68.676
.856
38
0.0
4.9
2.041
70.717
.861
Results from the lower shore
No.
Length
Aperture
Length /Aperture
Cumulative
Running mean
2.2
6.6
.848
.848
.848
2
2.3
6.6
.864
3.712
.856
3
8.6
5.7
.509
5.221
.740
4
2.2
6.4
.906
7.127
.782
5
0.6
5.9
.797
8.924
.785
6
0.1
6.0
.683
0.607
.768
7
0.4
6.8
.529
2.136
.734
8
9.1
5.4
.685
3.822
.728
9
9.1
5.6
.625
5.447
.716
0
0.2
6.4
.594
7.040
.704
1
0.6
6.0
.767
8.807
.710
2
2.7
6.3
2.016
20.823
.735
3
2.7
6.2
2.048
22.871
.759
4
1.4
6.4
.781
24.653
.761
5
9.0
5.4
.667
26.319
.755
6
0.8
5.6
.929
28.248
.765
7
6.6
4.6
.435
29.683
.746
8
2.7
6.4
.984
31.667
.759
9
0.6
6.2
.710
33.377
.757
20
9.5
5.2
.827
35.204
.760
21
0.5
6.7
.567
36.771
.751
22
0.2
5.6
.821
38.592
.754
23
0.5
6.5
.615
40.208
.748
24
7.3
4.5
.622
41.830
.743
25
1.5
6.2
.855
43.685
.747
26
9.7
5.5
.764
45.448
.748
27
0.1
5.2
.942
47.391
.755
28
1.8
6.0
.967
49.357
.763
29
8.1
4.6
.761
51.118
.763
30
0.8
6.1
.770
52.889
.763
31
0.7
5.5
.945
54.834
.769
32
9.7
5.8
.672
56.506
.766
33
1.6
6.0
.933
58.440
.771
34
1.8
6.8
.735
60.175
.770
35
0.8
6.0
.800
61.975
.771
36
2.1
6.7
.806
63.781
.772
Anomalies
Mostly my results are consistent and this is shown by the running mean which has very similar values throughout. The shape of the running mean graph is also a very standard shape, so my results must be near perfect.
However, result '17' for the lower shore seems to be different, its ratio is the lowest from all the results and its length is also greatly different from the others. It doesn't affect my results significantly. I think a possible reason for the difference, judging by its size, is that it is an evolved species of gibbula umbilicalis which are smaller than the regular form. Also the fact that they were smaller made them harder to measure accurately with the callipers. I decided to ignore the result, because, although it didn't seem to effect the results, when I carried out analytical tests I didn't want it to effect these.
Interpreting and evaluating
Data Processing
Here are some calculations from both sets of results:
Upper Middle
Lower
Average
.861
.772
Standard Deviation
0.162
0.151
No. of Results
38
36
I will perform a 't-Test' on my results this will hopefully show whether or not there is a significant difference between the sets of results. The test is explained with the formula in the Appendix. My null hypothesis is: "There is no significant difference between the two sets of results"
The calculated 't' value is 2.453.
Using the table in the appendix to find the critical value, knowing that my level of significance is 0.05 and my degree of freedom is 72, I find that my critical value is 1.960. my 't' value is greater than this so I can reject my null hypothesis and therefore state that there is a significant difference between the ratio of length:aperture from the lower shore to the upper-middle shore.
Biological principles
Conclude: there is a difference , maybe need large length hold more water, small aperture to decrease water loss in upper , because of respiration.
The gibbula umbilicalis in the middle shore have a larger ratio of length over aperture than the ones in the lower shore. This means they have a relatively larger length and smaller aperture.
The length of the shell would determine the size of the shell and the larger the shell the larger the area inside the shell. Topshells hold water inside their shells. water is required for topshells to respire. I believe that the gibbula umbilicalis on the middle shore have adapted to spending longer periods of time out of water, by having a larger shell to hold more water in.
The aperture, as an opening in the shell, would normally allow water to pass out of the shell. This would be bad as the water which the topshells need to respire would be leaving the shell. I believe that the topshells in the middle shore have adapted to being out of water for longer periods of time, because they have relatively smaller apertures and larger shells, this means they can hold more water and not lose as much of it through the aperture as the aperture is smaller and would not allow as much water to pass out as it would if it were bigger.
This shows a good example of how creatures on the rocky shore have evolved and adapted to survive the competition for a place in the ecosystem of the rocky shore. By adapting to the harsher environment further up the shore, with less time under water, they can inhabit an area that has less competition, because other species could not live in the harsher conditions.
Limitations
I believe that my results are very reliable as the closeness of them shows they are an accurate reflection of the length and size of aperture of gibbula umbilicalis on the rocky shore. The accuracy is a good sign that they are reliable. By controlling lots of variables I made sure that the results were reliable. The abiotic factors were the same at both heights and so this proves that the results were not affected by them. So in consideration my results are reliable.
Appendix
Shell measuring method
= Measured distance
Cross-section of a Cross staff
Risk assessment
Risk assessment
Severity:
1=slight inconvenience - with verbal reassurance the activity can continue
2=minor injury - after first aid the activity can continue
3=injury/illness - medical attention required, activity can not continue
4=Major injury - hospitalisation/ use of emergency services
5=Fatality
Likelihood:
1=highly unlikely
2=may not occur
3=does occur
4=occurs from time to time
5=likely to occur
Risk = severity x Likelihood
If > 8 then bring attention to the group and use supervision
If > 10 activity must not go ahead
Preliminary results
Below are the results from my preliminary experiment. I counted the number of Gibbula Umbilicalis found inside my quadrat as I did a transect, with 0.6 m intervals, down the rocky shore.
Height
count 1
count 2
0
0
2
0
0
3
0
0
4
2
5
2
0
6
2
3
7
6
6
8
29
22
9
2
5
0
9
8
't -Test'
The t test uses two sets of results and produces a 't value' using the formula:
After you have a t value you need a critical value. They can be found from this table:
As my degree of freedom is more than 30 I use the degree of freedom ?. My level of significance is 0.05 so therefore my critical value is 1.960
If t < critical value then you must accept the null hypothesis
If t > critical value then you must reject the null hypothesis
Michael Cutting 13MD Biology Coursework
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