[R] Effect size in mixed models

[Bruno L. Giordano]

Hello,
Is there a way to compare the relative relevance of fixed and random effects 
in mixed models? I have in mind measures of effect size in ANOVAs, and would 
like to obtain similar information with mixed models.

Are there information criteria that allow to compare the relevance of each 
of the effects in a mixed model to the overall fit?

Thank you,
    Bruno