The results of The Mann-Whitney U-Test are documented on the following page by the use of a table and statistical valuations.
HEDGEBANK A HEDGEBANK B
N of q/rats
N of G.R.
Rank
N of q/rats
N of G.R.
Rank
1
5
13
12
8
19.5
2
3
5.5
13
5
13
3
4
9.5
14
3
5.5
4
6
16
15
4
9.5
5
2
2.5
16
9
21
6
3
5.5
17
7
18
7
1
1
18
6
16
8
4
9.5
19
5
13
9
3
5.5
20
8
19.5
10
2
2.5
21
4
9.5
11
6
16
R=144.5
N1 = number of results in the smallest group (Hedgebank B)
N2 = number of results in the largest group (Hedgebank A)
R = score of adding the ranks from the smallest group
The following equations are used to work out the values for U1 and U2.
U1 = N1N2 + N1(N1+1) - R U2 = N1N2 - U1
2
U1 = 10 x 11 + 10(10 + 1) - 144.5 U2 = 10 x 11 - 20.5
2
U1 = 110 + 10(11) - 144.5 U2 = 110 - 20.5
2
U1 = 110 + 110 - 144.5 U2 = 89.5
U1 = 110 + 55 - 144.5
U1 = 20.5
The smallest value of U = 20.5
The critical value = 26 (this is taken from the statistical table)
Because the U value is lower than the critical value there is a significant difference between the distribution of Geranium robertianum on the two hedgebanks, (The Null Hypothesis is rejected).
As we have not been given the precise abiotic environments of each hedgebank, we can only hypothesise as to the why there is a significant difference between the two hedgebanks.
There could be a wide range of elements affecting the diversity, these could possibly include edaphic, climatic and topographic factors. Edaphic factors are those that are related to soil, such as the pH value or particle size. To terrestrial organisms soil is particularly important. An example of this is that on hedgebank A the soil could be more acidic than that on hedgebank B. If the Geranium robertianum thrived more in less acidic soil, this could account for their increased distribution on hedgebank B. This would also work in reverse if hedgebank A soil was less acidic and Geranium robertianum preferred more acidic soil.
Climatic factors such as water, temperature, light and wind could also affect distribution. As light is very important for growth of a plant populations it could affect Geranium robertianum if they were in the shade of shrubs and trees all of the time. If hedgebank B was facing south it would receive more light and heat energy, this would increase the growth and distribution of the vegetation including Geranium robertianum, compared to that on hedgebank A. Lack of shelter could also contribute to differences in distribution.
Topographic factors include altitude, slope and the aspect of area. Slope is important as it reduces the chance of the soil becoming waterlogged. On the other hand, if the slope was too steep the soil could not form so plants would not be able to establish themselves. Hedgebank A could have less vegetation if it did not have a slope at all or if the slope was too steep.
As both hedgebanks surround cultivated fields which contain different kinds of crops, another factor here could be the use of insecticides and pesticides by the farmers. If more of these substances were used in the fields surrounding hedgebank A then this could have an affect on the growth and population of Geranium robertianum. Other factors that could possibly affect distribution could be the competition from other species, more insects that could damage or destroy the vegetation and also pollutants.
BIBLIOGRAPHY
PRINCIPLES AND PROCESSES
ROBERTS MICHAEL, REISS MICHAEL, MONGER GRACE
BIOLOGY A FUNCTIONAL APPROACH
ROBERTS M B V
BIOLOGY
BARBER MARCUS, BOYLE MIKE, CASSIDY MIKE, SENIOR KATHRYN
