[R] MCMC glmm

[garciap]

Hi to all the people,

I'm working with abundance data of some species, but containing too zero
values, and the factors are the ones typical in a BACI experiment
(Before-and-After-Control-Impact). Thus, these are two fixed factors. As the
data does not holds the normality and homogeneity of variances assumptions
of clasiccal ANOVA, I'm trying to fit a zero-altered model using the MCMC
glmm library.
I've two questions:

1.- how I can include an interaction between the BA (before and after) and
the CI (control-impact) components in this kind of models? I'm searching in
the notes available in the models but found no clear answer. My first
approach to this wil be to wrote a formula like: Abundance~BA+CI+BA*CI.
2.- Even when I try to fit a model without interactions I can't do it
because I obtain the following error:
> fit<-MCMCglmm(Abundancia~BA+CI, random=NULL,
> family="zapoisson",data=Trucha)
Error in MCMCglmm(Abundancia ~ BA + CI, random = NULL, family = "zapoisson", 
: 
  please use idh(trait):units or us(trait):units or trait:units for error
structures involving multinomial data with more than 2 categories or
zero-infalted/altered/hurdle models

I don't know where is the problem, maybe because my original data is
organised as (obviously with much more data):

Abundance    BA    CI
5       1    1
3       2    1
6       1    2


Any idea or suggestion? Many thanks for your help and patience, best regards


Pablo
8       2    2
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