"Let me paraphrase what you wrote to see if I understand. You have a number of plots each populated with a variety of plant species" OK, "and you are interested in only two of those species." No, I'm interested in the whole plot composition! I would like to understand if there are differences in terms of life forms composition beteween two groups of plots (each group has 70 plots). A simple t-test or other non parametric tests do not work fine with count data, as in my case. In addittion some life forms are uncommon so I have a lot of zero count in my data! You ask if there are meaningful in the relative abundances of each of your two species of interest in the plots. Inviata dal mio Windows Phone
life forms spectrum analysis
2 messages · Ludovico Frate, Rich Shepard
On Mon, 16 Mar 2015, Ludovico Frate wrote:
No, I'm interested in the whole plot composition! I would like to understand if there are differences in terms of life forms composition beteween two groups of plots (each group has 70 plots). A simple t-test or other non parametric tests do not work fine with count data, as in my case. In addittion some life forms are uncommon so I have a lot of zero count in my data!
Ludovico, Then you definitely should look at CoDA because, as you write above, you are looking to see if there are differences betwee the compositions of the two groups, and there will be compositional differences within each group that need to be distinguished from the between-group compositions. ven den Boogaart and Tolosana-Delgado's book, "Analyzing Compositional Data with R" is highly recommended. There are also abundant references on the Web, such as Pawlowsky-Glahn, Egozcue, and Tolosana-Delgado. 2007. Lecture Notes on Compositional Data Analysis. HTH, Rich