Death rate prior
The death rate prior is the prior on the relative death rate of the birth-death tree prior.
Let \(\lambda\) be the birth rate, and \(\mu\) be the death rate of the model then \(m = \mu/\lambda\). Since \(\mu\) and \(\lambda\) are rates, thus positive, \(m\) is lower bounded by 0. If \(m>1\) this implies \(\mu>\lambda\) thus extinction exceeds speciation and we should expect the process to produce no taxa. It is reasonable to assume \(0<m<1\). Unless there is more information available, a uniform(0,1) prior on \(m\) seesm reasonable.