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Figure 8.10 shows the dendrogram produced by hierarchical agglomerative clustering
with group-average linking of all 48 samples, i.e., the 6 patch and 6 non-patch
replicates for each of April, August and December 1997, and August 1998. The
dendrogram shows that most replicates within sites cluster with greater similarities
between each other than they do with replicates between sites. Additionally, the
dendrogram suggests that the August 1998 communities were very dissimilar to those
of the 3 previous sampling months. Figure 8.11 shows the 2-dimensional MDS
ordination plot of this dendrogram, with groups formed by patch and non-patch
replicates defined. Non-patch replicates are labelled as 'N' rather than 'NP' for this
plot due to the large number of points. This plot allows an assessment of the temporal
changes in both patch and non-patch community structures.
There is very little overlap between the patch and non-patch replicates in Figure 8.11
which implies that the community differences between these two plot types were large
compared to temporal effects. However, temporal effects are noticeable. Although
there was very little change in community structure from April to August 1997,
replicates for December are positioned predominantly on the left of the MDS plot.
The community change which occurred during August 1998 is also very apparent
from the MDS and these replicates are located on the right of the plot with a clear
separation from the others.
Table 8.4 presents the results from the SIMPER program on PRIMER. This program
calculates the relative contribution of each species to the total dissimilarity between
groups (patches and non-patches), the 3 species with the highest percentage
dissimilarity each month are shown in Table 8.4. The main species responsible for the
statistical differences in faunal communities between patch and non-patch areas were
C. edule, C. volutator and C. capitata, with P. cornuta, M. balthica and oligochaetes
(mainly tubificids) being influential at certain times of the year.
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