dear all,
I would like to ask your help on the following model:
I have data for the size of zooplankon in lakes with (Y) and without (N) introduced fish. there are 15 size classes with 1 the smallest and 15 the largest. Number of zooplankton samples in each class are as follows (cumulated over all lakes):

> Ctable
    
         N     Y
  1   7901 24174
  2   2869  2331
  3    964   737
  4   1573   621
  5   1857   584
  6   2073   777
  7   2078   548
  8    919   171
  9    485    28
  10   239     3
  11    64     0
  13    30     0
  14     3     0
  15     1     0

To test the hypothesis that fish eat the biggest zooplanktons, 
as I have repeated measures in different lakes, I thought to model this data as follows,: 

prior=list(R=list(V=1, fix=1), G=list(G1=list(V=1, nu=0)))
mod1<-MCMCglmm(CLASS~Fish-1, random=~lago,family="ordinal",data=dimensioni.dat, prior=prior)

where CLASS is the size class and "Fish" the variable indicating if the lake has or not introduced fish. 

The model seems to run fine, but I have trouble in obtaining the expected probabilities for each size category in lakes with and without introduced fish... Anybody can help me out?

your help would be greatly appreciated!

cheers,
Achaz von Hardenberg  
Gran Paradiso National PArk. Italy


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