... as regarding the "recognition" of groups in a continuum without prior group assignment, one method not mentioned so far is mixture modelling, which is simply attempting to fit the data to a mixture of e.g. gaussians. Criteriae such as the Akaike Information Criterion may be used to get some idea about a "reasonable" number of groups, although a proper significance test is not really available.
And then you have all those old clustering methods, including more or less desperate attempts to calculate some kind of significance (beware). If the points are assigned to groups from independent information, there are the standard statistical tests. Since you are primarily interested in PC1, a one-way ANOVA might be sufficient, although I think a MANOVA on all PCs would be better. All these methods are available in e.g. R or PAST. Oyvind Hammer Natural History Museum University of Oslo -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
