[R-sig-eco] Binomial GLM: Is it the right way?

[Ludovico Frate]

Dear List,
I'am trying to fit a GLM with a binomial error distribution but I am a little bit confused about the model.
I have 24 vegetation permanent plots, randomly distributed, sampled two times: 1962 and 2009. I am looking for any changes in vegetation composition and in particular based on plant traits (life forms).For each species, I assessed whether it had colonized (i.e. been in 1962 absent but in 2009 present) or become locally extinct (i.e. been in 1962 present but recently absent) in the plot.I would like to analyze whether a species trait affected the likelihood of colonizing or becoming extinct on a summit.
example: Colonizing species
Traits	TOTAL	COLONIZING	PROB_COLChF		24		0			0ChC		24		1			0,041666667ChR		24		11			0,458333333ChSC	24		1			0,041666667ChS		24		18			0,75Ph		24		2			0,083333333Geo		24		18			0,75HeB		24		1			0,041666667HeC		24		36			1,5HeR		24		47			1,958333333HeS		24		161			6,708333333Th		24		28			1,166666667

Traits is the plant trait analyzed, TOTAL is the number of plots and COLONIZING represents the number of new species found in 2009 per plot, PROB_COL is the probability of colonization (COLONIZING/TOT)
However PROB_COL is >1, so I think that TOTAL should be different (i.e. total number of colonizing species)?
Any suggestions?Thank you,Ludovico
                                                                                                                                
Ludovico
Frate

PhD student (University of Molise - Italy)
Environmetrics Lab
http://www.distat.unimol.it/STAT/environmetrica/organico/collaboratori/ludovico-frate-1
Department of Biosciences and Territory - DiBT
Università del Molise.
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E-mail ludovico.frate at unimol.it
ludovicofrate at hotmail.it

 		 	   		  
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