  Asymptotic behaviour of conditional $\alpha$ diversity for the two-parameter
Poisson-Dirichlet partition model and for the normalized generalized Gamma
model has been recently investigated in Favaro et al. (2009, 2011) with a view
to possible applications in Bayesian treatment of species richness estimation.
Here we generalize those results to the larger class of mixed Poisson-Kingman
species sampling models driven by the stable subordinator (Pitman, 2003).
