Munoz François, Couteron Pierre, Ramesh B R, Etienne Rampal S
French Institute of Pondicherry, 11 Saint Louis Street, Pondicherry 605001, India.
Ecology. 2007 Oct;88(10):2482-8. doi: 10.1890/07-0049.1.
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.
S.P. 哈贝尔的中性理论假定了一个双尺度层次框架，该框架由一个遵循以“生物多样性数量”θ为特征的物种形成 - 漂变平衡的集合群落，以及遵循以“迁移率”m（或“基本扩散数”I）为特征的迁移 - 漂变平衡的局部群落组成。虽然艾蒂安的抽样公式允许从局部群落的单个样本中同时估计θ和m，但其对（相当小的）样本网络的适用性值得怀疑。我们在此定义一种替代的两阶段方法，即从实地采样个体的适当子集中估计θ（使用尤恩斯抽样公式），并从群落样本中估计m（使用艾蒂安抽样公式）。我们将其结果与对θ和m的同时估计（单阶段估计）进行比较，用于模拟中性样本以及印度南部50个1公顷常绿森林样地。单阶段方法存在偏差问题，并且在高θ、低m和低θ、高m解域之间的可区分性较差。相反，两阶段方法产生了合理的估计，并且当有几个小的、分散的样地而非单个大样地时更可取。
