Hi Ricardo,

try using MCMCglmm() from the MCMCglmm package. It's advantage is that it
estimates overdispersion (in the form of residual variance) for Poisson
distributed data using additive overdispersion. During my classes I've
shown many times using simulated data that it deals perfectly with
overdispersion yielding unbiased estimates. Check out Jarrod Hadfield
Course Notes for more details.

Cheers,
sz.

-- 
Szymon Drobniak || Population Ecology Group
Institute of Environmental Sciences, Jagiellonian University
ul. Gronostajowa 7, 30-387 Kraków, POLAND
tel.: +48 12 664 51 79 fax: +48 12 664 69 12

www.eko.uj.edu.pl/drobniak

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