[R-sig-ME] advice with lmer syntax

[Giacomo Santini]

Dear all,

here is my problem, a very  simple one indeed. I am new to mixed models 
and before go on with the analysis I wish to be sure I am rigth in  
model formulation.

My data set consists of  observations on the behaviour (say time active, 
Activity) of marine animals. I have 120 individually marked animals in 
three different randomly chosen sites (40 animals per site). I was 
interested in assessing if the behaviour changed during A) different 
seasons and  B) different tidal conditions.
For each animal in each site the behaviour was observed during three 
different randomly chosen days within each combination of Season (A) and 
Tide (B). Obviously each individual is specific to one of the three 
sites. In summary:

Season, fixed factor, 2 levels (Summer,    Winter)
Tide, fixed, 2 levels (Neap and Spring)
Site, random factor, 3 levels
Animal, random factor, 120 levels, nested within Site

I wish to analyse this data set using lme4. I guess the starting model 
to answer to questions A, B and C is

Mod1<- lmer(Activity~Season*Tide + (1|Site)+ (1|Site/Animal) , 
data=obsTot, REML=TRUE)

Now if I wish to check if the effect of Season and Tide differs in the 
different sites (altough I am not interested in these tree sites in 
particular) would it be correct to add to Mod1 terms like 
(1|Season:Site) and or, (1|Tide:Site)? Something like:

Mod2<- lmer(Activity~Season*Tide + (1|Site)+ (1|Site/Animal) + 
(1|Season:Site)+ (1|Tide:Site), data=obsTot, REML=TRUE)

Any suggetion is welcome

Cheers
Giacomo

-- 
-------------------------------------------------------
Giacomo Santini PhD
Dipartimento di Biologia Evoluzionistica "Leo Pardi"
Universita' degli Studi di Firenze
Via Romana 17
I-50125 Firenze
Italy

Tel: +39 055 2288288 (DBE) - +39 0574 447727 (CESPRO)
Fax: +39 055 2288289
www.dbe.unifi.it/santini