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Suggested answers for
case study 9
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Jaccard and Dice coefficients
The most similar associations are the Stricklandia and Eocoelia
communities. Trends are difficult to see from the table.
Cluster analysis of taxa
The Lingula community (black) form a well-defined group, and the
Clorinda community (green) also shows up well except for the
exclusion of Eoplectodonta. The other taxa seem to be spread
across communities.
Detrended correspondence analysis of associations
The order of the associations along the first ordination axis is
Lingula, Eocoelia, Pentamerus, Stricklandia and Clorinda, in perfect
agreement with the onshore-offshore ordering.
Seriation
The seriation method also gives the 'correct' ordering of samples.
Cluster analysis of associations
The cluster analysis is in good agreement with the results above.
Remember that the PENTA-STRIC and EOCOE-LINGU pairs in the
dendrogram are arbitrarily oriented, so they can be reordered
to appear in the expected sequence.
To conclude, the environmental gradient is well supported by
several different analysis methods.