Table 2.

The output of the negative binomial generalized linear model for species richness with DBH ≥ 1 cm and ≥10 cm

Explanatory variables	$\widehat{\mathbf{\beta }}$	SE	z	Pr(>|z|)
DBH ≥ 1 cm)
Intercept	0.335	0.729	0.460	0.65
Region effect
Africa	−0.113	0.223	−0.505	0.61
Europe	−1.232	0.372	−3.310	9.31e-04
Nearctic	−0.653	0.253	−2.580	9.89e-03
Temperate Asia	0.307	0.222	1.385	0.17
Tropical Asia	0.377	0.152	2.483	0.013
Island	−0.407	0.117	−3.472	5.17e-04
log(ntree1)	0.347	0.055	6.355	2.08e-10
Isothermality (BIO3)	1.253	0.289	4.337	1.44e-05
Mean temp of warmest quarter (BIO10)	0.993	0.236	4.207	2.59e-05
Precipitation seasonality (BIO15)	−0.647	0.201	−3.215	1.30e-03
DBH ≥ 10 cm
Intercept	−0.599	0.873	−0.685	0.49
Region effect
Africa	−0.085	0.276	−0.307	0.76
Europe	−1.786	0.456	−3.913	9.11e-05
Nearctic	−0.823	0.337	−2.443	0.015
Temperate Asia	0.333	0.256	1.303	0.19
Tropical Asia	0.551	0.169	3.263	1.10e-03
Island	−0.431	0.134	−3.209	1.33e-03
log(ntree10)	0.424	0.069	6.163	7.14e-10
Isothermality (BIO3)	1.370	0.345	3.976	7.01e-05
Mean temp of wettest quarter (BIO8)	1.472	0.402	3.658	2.54e-04
Precipitation seasonality (BIO15)	−0.842	0.237	−3.546	3.91e-04

The log link function is $\log (\mu )=\mathbf{\beta }\mathit{x}$, where β is the vector of regression coefficients (including the intercept) and x is the vector of explanatory variables. The region effects were coded in reference to the Neotropical forests (the intercept). The effect of island (i.e., isolation effect) is in reference to the mainland plots; −0.407 for the island plots (for DBH ≥ 1 cm) indicates that species richness on islands is significantly (P = 0.0005) lower than that in the mainland plots (given that the effects of other variables were accounted for). The model was selected by stepwise procedure using the criterion of AIC.