Estimating parameters of neutral communities: From one single large to several small samples

The neutral theory of S. P. Hubbell postulates a two-scale hierarchical framework consisting of a metacommunity following the speciation - drift equilibrium characterized by the "biodiversity number'' theta, and local communities following the migration - drift equilibrium characterized by the "migration rate'' m ( or the "fundamental dispersal number'' I). While Etienne's sampling formula allows simultaneous estimation of h and m from a single sample of a local community, its applicability to a network of ( rather small) samples is questionable. We de. ne here an alternative two-stage approach estimating h from an adequate subset of the individuals sampled in the field ( using Ewens' sampling formula) and m from community samples ( using Etienne's sampling formula). We compare its results with the simultaneous estimation of theta and m ( one-stage estimation), for simulated neutral samples and for 50 1-ha plots of evergreen forest in South India. The one-stage approach exhibits problems of bias and of poor differentiability between high-theta, low-m and low-theta, high-m solution domains. Conversely, the two-stage approach yielded reasonable estimates and is to be preferred when several small, scattered plots are available instead of a single large one.