Canonical Correspondence Analysis

44

Biplot   This button presents a grid of the coordinates of the tip of the environmental

variable vectors used in the ordination biplots to show species relationships to the

environmental variable (see 

Rank Plot

).

Inter   This button presents the correlation between the environmental variables and

the site (sample) scores calculated using the weighted average of the species. It is

termed the Inter set correlation.

Intra    This button presents the correlation between the environmental variables and

the site (sample) scores calculated using the regression of the environmental

variables with the site scores derived from the species. It is termed the Inter set

correlation. It is always larger than the intra set correlation.

These results can be printed or exported from the File menu and copied from the Edit

menu. See 

Export Active Grid

.

7.16

Monte Carlo Simulations

Monte Carlo randomization tests are only undertaken if selected from the

Randomization drop down menu. This menu allows you to select 100, 1000, and

10000 trials. It is a good idea to initially run only a hundred simulations as this

procedure can take a long time if you have a large data set.

For each simulation the order of the samples in the sample species array is randomly

shuffled and the Eigenvectors calculated as usual. By shuffling the order of the

samples we are breaking the correlation between the environmental variables and the

species. Thus there will not be any relationship. The probability measure given in the

Monte Carlo output grid is the probability that an Eigenvalue as large as that observed

could have occurred by chance. Also given in the table is the largest and smallest

Eigenvalues observed and the mean Eigenvalue. The calculations are only undertaken

for the 3 axes with the largest Eigenvalues as it is unlikely that you will have

significant variation explained by subsequent axes.

Copyright 2004  PISCES Conservation Ltd