On Mon, 16 Mar 2015, Ludovico Frate wrote:
I would like to analyse the differences in life form (Raunki??) composition between two populations. The two populations (plant communities) were sampled randomly and the presence of plant species were recorded. So for each plot I have the frequency of each life form. First, I thought to a chi square or binomial test. However, I am worried about the applicability because both tests require that the frequency of life forms observed vs expected is grater than 0% (i.e., when a given life form is present in all the plot of both populations - observed = 100% expected = 0%) and less than 100% (better between 20 and 80%).
Pop1, Pop2 present, 70, 56 absent, 0, 0
Do you have any ideas about analysing differences in life forms?
Ludovico, 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, and you are interested in only two of those species. You ask if there are meaningful differences in the relative abundances of each of your two species of interest in the plots. If this is correct (or close to correct), I suggest that you look at these as compositions (the packages compositions, robCompositions, and zCompositions each offer useful functions). The number (or percent ground cover) of the species other than your two are immaterial. Assuming that the relative proportions of each of your two species are the response (dependent) variables, and you have potential explanatory (independent, predictor) variables, then you can perform regression analyses on the compositions. Hope this helps, Rich _______________________________________________ R-sig-ecology mailing list R-sig-ecology@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-ecology
