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

Munoz, François, Couteron, Pierre, Ramesh, B. R., Etienne, Rampal S.
Ecology 2007 v.88 no.10 pp. 2482-2488
community ecology, species diversity, plant communities, tropical forests, field experimentation, forest ecology, estimation, India
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” θ, 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 θ and m from a single sample of a local community, its applicability to a network of (rather small) samples is questionable. We define here an alternative two‐stage approach estimating θ 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 θ 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‐θ, low‐m and low‐θ, 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.