[R] Comparing GAMMs

[Paul Simonin]

Greetings!
  I am looking for advice regarding the best way to compare GAMMs. I 
know other model outputs return enough information for R's AIC, ANOVA, 
etc. commands to function, but this is not the case with GAMM unless one 
specifies the gam or lme portion. I know these parts of the gamm contain 
items that will facilitate comparisons between gamms. Is it correct to 
simply use these values for this purpose? For example, the lme portion 
of the gamm returns a log liklihood value that could be used to 
calculate information criteria. However, I am wondering whether entire 
gamms be compared using this, or only the lme part.
  Maybe my thinking about the lme and gam portions of gamms is 
incorrect? If this appears to be the case, let me know! In general, if 
someone could clarify my understanding in any way it would be much 
appreciated.
Thank you very much!
Sincerely,
Paul Simonin