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Community Analysis Package

9

Groups

This menu allows you to (1) assign individual samples to different groups, (2)

undertake an Analysis of Similarity (

ANOSIM

48

) and (3) Identify those species

which most contribute to the similarity (or dissimilarity) between samples

(

SIMPER

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).

Why does CAP allows you to assign samples to groups? You might for example

allocate a series of samples to polluted and control groups or in a benthic study to

different physical conditions such as mud, sand and gravel substrates. In another

type of study you might want to define as a group all samples that held a species

of particular interest.

By allocating samples to groups you can show the different groups in ordination

plots and other graphs.

For example, in the Powerfish example dataset supplied with CAP the species of

fish caught on different power station intakes the stations are grouped as

estuarine and marine. If a PCA is run on these data the two groups can be clearly

seen to cluster around different positions within the ordination space.

Once samples have been placed into groups you can test if the similarity of

samples within each group is greater than the similarity that would occur by

random chance using 

ANOSIM

48

.

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