[R-sig-eco] life forms spectrum analysis

[Rich Shepard]

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