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 theta 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 theta 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.
Munoz
François
F
French Institute of Pondicherry, 11 Saint Louis Street, Pondicherry 605001, India. francois.m@ifpindia.org
Couteron
Pierre
P
Ramesh
B R
BR
Etienne
Rampal S
RS
D000465:Algorithms; D000818:Animals; D044822:Biodiversity; D004463:Ecology / Q000379:methods*; D017753:Ecosystem; D016013:Likelihood Functions; D008954:Models, Biological; D011157:Population Dynamics; D013045:Species Specificity; D014197:Trees / Q000254:growth & development*