Obtaining help
restoration on biodiversity in several chalk streams in southern England. The
report on the investigation, 
Effects of physical restructuring of channels on the
flora and fauna of three Wessex rivers
, can be downloaded in Adobe Acrobat
PDF format from our website at
Concentrating on macroinvertebrates, the data comprise percentage composition
by family from restored and unrestored reaches of the 3 rivers and 2 tributaries.
There are 61 families (rows) across 49 sample sites (columns).
The site names are coded with the initial letter of the river and  U  or  R  for
unrestored or restored. The rivers are the Wylye, its tributary the Till, the Piddle,
its tributary the Devil s Brook, and the River Avon. So for instance, the unrestored
stretch at Hyams Farm on the Avon is coded Ahyam U, and the restored site at
Great Wishford on the Wylye is coded Wgwish R.
To begin the example, open the data file 
 from the File menu. On opening the file, a warning
box pops up, to inform you that the row titled  Hydrida  has no data   i.e. all the
values are zero. The program will automatically remove this row from the
Working Data
Let us first perform a Principal Components Analysis; from the Ordination menu,
choose PCA   Covariance. Click on the PCA Plot tab which appears at the
bottom, to view the resulting chart (shown below with all labels removed, for
clarity). Note that, because the PCA depends on a randomisation of the data, the
chart may appear as a mirror image of the one below. This is unimportant.
Immediately, we can see that most of the species vectors are tightly grouped in
the centre of the plot, but there are 3 strong vectors and a number of sites
associated with them. By experimenting with the labelling, we can see that the
three families are Simuliidae, Hydrobiidae and Gammaridae. By looking at the
site labels, it becomes obvious that the 8 sites plotted in a line to the right are the

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