Hi Ludovico,
You can compare the proportion of each life form using logistc regression,
an example with simulated data for 20 plots:
set.seed(100)
n<-20
population<-sample(c("A","B"),n,replace=T)
lifeform1count<-round(runif(n,0,100),0)
otherlifeformscount<-round(runif(n,0,100),0)
f<-glm(cbind(lifeform1count,otherlifeformscount)~population,family=binomial)
summary(f)#significant difference between populations p=0.01137
plogis(coef(f)[1])#mean proportion of life form 1 in population A
plogis(coef(f)[1]+coef(f)[2]) #mean proportion of life form 1 in population
B
You can run one model for each life form, but maybe multinomial regression
is more correct (never tried)
Aitor
-----Mensaje original-----
From: Ludovico Frate
Sent: Monday, March 16, 2015 6:07 PM
To: r-sig-ecology at r-project.org
Subject: [R-sig-eco] life forms spectrum analysis
Dear List,
I would like to analyse the differences in life form (Raunki?r) 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
I have tried also a simple Mann whitney test but it doesn't work well for
count data. In addition for uncommon life forms I have a lot of zero counts
in my data!
Do you have any ideas about analysing differences in life forms?
Best,
Ludovico
Dott. For. Ludovico
Frate, Ph.D.
University of Molise - Italy
Environmetrics Lab
http://www.distat.unimol.it/STAT/environmetrica/organico/collaboratori/ludovico-frate-1
Department of Biosciences and Territory - DiBT
Universit? del Molise.
Contrada Fonte
Lappone,
86090 - Pesche (IS)
ITALIA.
Cel: ++39
3333767557
Fax: ++39 (0874) 404123
E-mail ludovico.frate at unimol.it
ludovicofrate at hotmail.it
https://www.researchgate.net/profile/Ludovico_Frate
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