[R-sig-ME] Fitting GLMM to percent cover data with glmmTMB

[Vasco Silva]

 Hi,

I am trying to fit a GLMM on percent cover for each plant species:

>str(cover)
'data.frame': 100 obs. of  114 variables:
$ Plot : Factor w/ 10 levels "P1","P10","P2",..: 1 1 1 1 1 3 3 ...
$ Sub.plot: Factor w/ 5 levels "S1","S2","S3",..: 1 2 3 4 5 1 2 ...
$ Grazing : Factor w/ 2 levels "Fenced","Unfenced": 1 1 1 1 1 1 1  ...
$ sp1 : int  0 0 0 1 0 0 1 ...
$ sp2 : int  0 0 0 0 0 3 3 ...
$ sp3 : int  0 1 0 0 1 3 3 ...
$ sp4 : int  1 3 13 3 3 3 0 ...
$ sp6 : int  0 0 0 0 0 0 0 ...
 ...
$ tot  : int  93 65 120 80 138 113 ...

I was wondering whether the GLMM can be fitted with glmmTMB (tweedie
distribution) and if so, should I use percent cover or percent cover
converted to relative abundance?

sp1.glmm <- glmmTMB (sp1 ~ Grazing + (1|Plot), data=cover, family=tweedie
(link ="logit"))

Any advice would be very much appreciated.

Cheers.

Vasco Silva

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