Extracts from this essay...
ECOLOGY ASSIGNMENT INVESTIGATION INTO THE NUMBER OF GERANIUM ROBERTIANUM ON TWO DIFFERENT HEDGEBANKS A student was investigating the hedgebanks surrounding two cultivated fields. Each field contained a different crop. They were situated approximately 1 mile apart. Using random quadrats the student recorded the distribution of the cranesbill Geranium robertianum on the two hedgebanks. The results are shown below. Number of Geranium robertianum per quadrats HEDGEBANK A 5 3 4 6 2 3 1 4 3 2 6 HEDGEBANK B 8 5 3 4 9 7 6 5 8 4 Q1. Was there a significant difference between the distribution of Geranium robertianum on the two hedgebanks? (Give reasons for the test chosen and the conclusion reached) Q2. Suggest possible reasons for any differences in vegetation between the two hedgebanks. I have decided to choose the Mann-Whitney U-Test to determine if there is a significant difference between the distribution of the Geranium robertianum, on the two hedgebanks.
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.
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.
Found what you're looking for?
- Start learning 29% faster today
- Over 150,000 essays available
- Just £6.99 a month
- Over 180,000 student essays
- Every subject and level covered
- Thousands of essays marked by teachers