binomial regression with non integers

Dear all,

I am investigating diversity in different sites. I partitioned my measure of diversity into to additive components (Baselga 2012) and get for each site a value of overal 
diversity change (between 0 and 1) and a value for each additive component, such that for each site beta1+beta2=beta_total. I would like to make a regression 
model to test if the proportion of diversity due to beta1 (beta1/beta_total) is signifcantly different according to an explanatory factor. If beta1 had been an integer 
value, I would have used a binomial model. However, since beta1 is not an integer I don't think that I am allowed to use the formel 
glm(cbind(beta1,beta2)~x,family=binomial)? What alternative method could I use?
I hope that my question is not too confuse. 
Thank you very much.
Val?rie
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