Various items of supplementary material related to the books in this series can be found at the following links:

Multivariate Analysis of Ecological Data

cc.oulu.fi/~jarioksa/opetus/metodi/vegantutor.pdf
OKSANEN J. Multivariate analyses of ecological communities in R: vegan tutorial. 43 p.
This compact tutorial to the R package vegan is a very useful, brief introduction to the application of multivariate statistics in community ecology.
ordination.okstate.edu
PALMER M.W. Ordination methods for ecologists
The web site is a very useful overview of ordination methods, providing links, references, and guides for self study, including a much needed glossary.

Biplots in Practice

www.carme-n.org
Correspondence Analysis and Related Methods Network, with R scripts and data from Biplots in Practice, Correspondence Analysis in Practice (second edition), and from Multiple Correspondence Analysis and Related Methods.
www.r-project.org
The R project for statistical computing.
deleeuw.rbind.io/
Jan de Leeuw's website for the Gifi system (centred around multiple correspondence analysis and related methods) and R functions.
www.imperial.ac.uk/bio/research/crawley/statistics
Michael Crawley's material from his book Statistics: an Introduction Using R.
www.issp.org
Source of many data sets from the International Social Survey Program.