Fig. 2: Relationships between intraspecific trait variability (ITV) and competitiveness of species.

a, d, Pairwise experiments in homogeneous environments (n = 345 and 661 seedlings, respectively). b, e, Multispecies experiments in homogeneous environments (n = 132 and 121 seedlings, respectively). c, f, Multispeices experiments in heterogeneous environments (n = 1005 and 916 seedlings, respectively). ITV per species was quantified by the 999 simulated hypervolume of seven traits (measured in SD⁷ units), and competitiveness was quantified using the relative interaction intensity index (RII) based on whole seedlings’ biomass. Gray (a, d), blue (b, e), and purple (c, f) points with error bars represent the mean and standard error of the 999 simulated hypervolumes for each competing species, transformed by cube root. Hollow points and solid points represent species under competition-free and competition treatments, respectively. Detailed sample sizes for each competing species in two-phase experiment are shown in Table S4. The orange dots in a and d represent the mean ITVs of the eight superior (or inferior) species. The gray and orange line connecting these dots visually depicts the difference in ITV between competing species, and significance was tested by one-sided paired Wilcoxon rank-sum test. Black asterisks indicate levels of significance (•: <0.1; *: <0.05; **: <0.01; ***: <0.001). NS indicates nonsignificant. In b, c and d–f, solid (P < 0.05) and dashed (P > 0.05) lines are simple linear regression lines with 95% confidence intervals.