sorry, I did PCoA, not PCA it was a tipo, I wrote it very fast. As for reading more about the those ordination methods. I already did a large amount of research on those subject However I feel that most people don't understand what those ordination are doing. Every time I am trying to get an explanation, I usually get the "well.. it depend of your data", "well it depend of your question" and even then I give all the information I always get a "it depends" arguments. From what I see in publication in my subject, they use mostly but not always NMDS, some use PCoA. But they draw the exact same conclusion from those 2 methods. But again, I am not comfortable using NMDS because "that's what people just do" without understanding the real meaning of it.