Worked Example
84
13
Worked Example
This Section gives an example of the use of ECOM. It is based on the well known Dune
Meadow data  set used by Jongman et al. (1995).
The objective of the analysis is to determine if  there any gradients in the species data
that can be explained by the environmental variables.
The data files are supplied with the ECOM installation.
First open the species abundance file using the Biological File drop down menu. This
file holds the dependent variables and is named Dune_species.csv.
Now open the file of environmental variables using the Environmental File drop down
menu. This file holds the independent variables that may influence species abundance
and is named Dune_enviro.csv.
We will now take you through the stages of a typical Canonical Correspondence
Analysis. The purpose of this analysis is to identify the environmental variables that
are most important in moulding the plant community. The stages of this process are
described in turn below.
Preliminary inspection and data transformation
Examine and Select Environmental Variables
Interpreting the results
13.1
Preliminary inspection and data transformation
Having opened the data sets the species and environmental data will be presented in
grids. The raw species and environmental data is viewed by clicking on the
Sample/Species Data and Environmental Data tabs respectively. The data sets
can be changed and transformed from the working data tabs.
Changes made to the working data will not change the raw data.
We will not undertake any transformations on the Dune Meadow data set. This is
because the numbers in both the environmental and species data sets are both with a
single order of magnitude.
We can find out about the range in our data using the Summary tab. Below it can be
seen that the largest maximum environmental variable value is 11.5 and the smallest
is 1. A similar inspection should be undertaken on the species data.
Copyright 2004  PISCES Conservation Ltd





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