Coexistence and the Strength of Stabilization
Plots of fitness equivalence (\(\frac{R_{\max,j}}{R_{\max,i}}\)) overOij showed that almost all species pairs have sufficiently similar fitness to satisfy the coexistence conditions expressed by equation 1, even as Oij approaches 1 (Fig. 3a). Only 18 of 166 species pairs fell outside the zone for coexistence (14 when R max was estimated using allometric regression; supplementary Fig. S5). A similar pattern was found when comparing one species j with the average of all others (Fig. 3b). There was no evident trend of a change in fitness equivalences along the overlap gradient, implying that most species (or species pairs) have sufficiently similar fitness that coexistence is stable for virtually any level of niche overlap. The strength of the stabilizing effect of niche differences is such that, in most cases, niche overlaps were between 50 and 100% smaller than the minimum necessary to enable coexistence (Figs 3c and d). The median of the percentage difference between observed and minimum permissible overlap was high (0.73), with an interquartile range from 0.40 to 0.95.