[R-sig-ME] lme4 - GLMM dispersion parameter?

[Liam Crowther (BIO)]

Dear list users,

I'm using lme4 to model the densities of several bee species in response to landscape gradients. For some species I've used just a random intercept and for others I've allowed a random effect of forage quality, this is determined by comparing maximal models with the different random components before refining the fixed effects. The dependent variable is a count at at a transect of which there are repeated measures so I'm using a GLMM with Poisson errors, examples of final models below:

hy25<-glmer(Bh~+DATE+bees$X250PCURB+bees$X250PCOSR+bees$X250PCWOO+ (1|TRANSECT), data = bees, family =poisson)

b23<-glmer(BtA~FORAGE.ST+DATE+bees$X250PCURB+bees$X250TE+bees$X250PCSNA+bees$X250PCWOO+ (1+FORAGE.ST|TRANSECT), data = bees, family =poisson)

In total there are 338 observations of 42 subjects, is there a general method for extracting a dispersion parameter from models such as these (there are models for 7 spp. at 3 different scales) where there are differing numbers of predictors and random effects?

Thank you

Liam Crowther