Species diversity on the Ynyslas sand dunes.
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Species diversity on the Ynyslas sand dunes For this work we went to the Rheidol study centre near Aberystwyth in Wales. From here the field work was carried out on the Ynyslas sand dunes near the River Dovey mouth on the west coast of Wales (see map). Sand dune formation To form the following things are needed: supply of sand wind stabiliser Stage 1 - Sand particles are transported by the prevailing wind by the process of saltation. If there is a stabiliser, an obstacle, sand is deposited on the leeward side where it can no longer be picked up be the wind. The grains build up and form a small dune. Stage 2 - Dune continues to grow and in colonised by pioneer species such as marram grass. The roots bind the sand and the shoots trap more sand and an embryo dune is formed. Stage 3 - The dune increases in size and is colonised by further species, making it more stable. New dunes form in front of older ones. The unique formation system of sand dunes leads to plant succession and zonation on the dunes. While doing trail work on dune vegetation I noticed that the number of species present increased as the age of the dunes increased. I can see from research that the probable reason for this is that the older dunes are at a later stage of succession than the younger ones so will have a higher diversity of plant species.
meters from rank number of rank D D² 1st dune species 0 1 0 1.00 0.00 0.00 50 2 1 2.00 0.00 0.00 100 3 3 3.00 0.00 0.00 150 4 6 4.00 0.00 0.00 200 5 7 5.50 -0.50 0.25 250 6 9 8.00 -2.00 4.00 300 7 7 5.50 1.50 2.25 350 8 8 7.00 1.00 1.00 400 9 10 9.00 0.00 0.00 450 10 11 10.00 0.00 0.00 ?D²=7.5 Rs = 1 - 6?D² = 1 - (6 x 7.5) = 1 - 45 = 1 - 0.0455 n(n² - 1) 10(10² - 1) 990 Rs = 0.955 Where: Rs is the Spearman rank correlation coefficient D is the difference between the 2 ranks n is the number of sets of data Critical values for Rs n 5 6 7 8 9 critical value 1.000 0.886 0.786 0.738 0.683 n 10 12 14 16 18 critical value 0.648 0.591 0.544 0.506 0.475 When compares to the critical value the Spearman rank coefficient of correlation is much larger. This allows the null hypothesis to be rejected as it proves that there is a significant correlation between the number of species and the distance from the 1st sand dune. The Rs value is positive therefore the correlation is positive. The results are significant at the 0.05 level. This means that the results would have occurred by chance in fewer than 1 in 20 occasions.
With no results it can not be proved that the embryo dune do follow the trend, but, from observation, there appeared to be only 1 species present, which indicates that they do follow it, thus supporting the conclusion. Time limited the size of the area that could be sampled. There was only time to do one transect and the sample intervals were increases from 30m to 50m for the same reason. From the earlier work on the dunes 50m sampling intervals were judged to be sufficient. The sand dunes cover a large area. The profile of the dunes and the position on blow outs and slacks changes though out this area. By only doing one transect the effect of these changes on species diversity could not investigated. Also it allowed only a relatively small area of the sand dunes to be sample. This could reduce the validity of the conclusion. As the results follow the typical pattern of species diversity discovered in research the conclusion drawn is most likely a valid one. The anomalous results do not limit the conclusion as they were investigated and a reason for them was found, therefore do not effect the conclusion made. To improve the investigation more time would be needed so more transects could be done. This would show more accurately the effect of distance from the 1st dune has on the species diversity by enabling a larger proportion of the dunes to be sampled. Also, if the embryo dunes could be sampled the results could be used to support, or undermine the conclusion.
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