StarBEAST has baked in prior on population sizes. There is no need for this.

[alexeid]

SpeciesTreePrior currently takes a gammaParameter that is used to parameterize the prior on popSize parameters. It would be simple to make gammaParameter optional, and then the user would be free to put any prior they like on the popSize parameters separately.

[rbouckaert]

Since we are refactoring anyway, we should move to the StarBEAST2 implementation, which is faster and allows for species tree linked clock models & integrating out pop sizes. So, perhaps looking into the StarBEAST2 priors makes more sense.