Dear Alan It would seem to me a better choice to use a Mantel test since you are looking at a specific contrast, if I remember PCOrd does that, if you are looking for software (they also publish a good general book on the subject)
--- Alan Griffith <[EMAIL PROTECTED]> wrote: > Hello all, > > I am gathering data this summer on species > abundances beneath 1) plots > covered by Ailanthus altissima and 2) plots not > covered by Ailanthus. I > will have replicate plot data from 4 different > sites. I would like to > explore the possibility that different species or > species types (e.g. > vines) may be more abundant under Ailanthus or more > likely to be found > under Ailanthus. I will have little information > about differences between > plots and sites aside from Ailanthus presence / > absence and light levels. > Even then, light levels will probably vary little > between plots. > > I've been sifting through a variety of information > on ordination as it may > relate to plant community data. If I understand > correctly, some > ordination process may be able to tell me if > Ailanthus plots cluster > together on an ordination axis. Michael Palmer, on > his ordination for > ecology website, presents a dataset organized by > species in rows > and "sites" in the columns. This would be one way I > might organize my > data. My difficulty is in understanding the > differences between the many > different ordination techniques and how to choose > which technique is > appropriate for our current task. > > I look forward to any suggestions from the list. > > Alan Griffith > Department of Biological Sciences > University of Mary Washington > <P>Abraham de Alba Avila</P> <P>Terrestrial Plant Ecology</P> <P>INIFAP-Ags</P> <P> Ap. postal 20,</P> <P> Pabellón Arteaga, 20660</P> <P> Aguascalientes, MEXICO</P> <P> Tel: (465) 95-801-67, & 801-86 ext. 118, FAX ext 102 alternate: [EMAIL PROTECTED] cel: 449-157-7070</P> __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
