Fig. 3.

Human impacts on fitness and on the opportunity for selection influence selection strength. (A) Distribution of mean absolute fitness, the variance in absolute fitness, and the opportunity for selection in natural (N) and disturbed (D) conditions across the 22 systems that reported fitness values. Gray circles are individual estimates, scaled within systems. Connected black and red symbols indicate the results of Bayesian mixed models (mode and 95% credible intervals of posterior distributions) estimating mean values in either condition. OS, opportunity for selection. (B) Effect size (log response ratio) of disturbance on selection strength as a function of the effect size of the same disturbance on either mean absolute fitness (Left) or on the opportunity for selection (Right). Symbols are individual systems. Positive values indicate systems for which disturbance increased selection strength, mean/variance in fitness, or the opportunity for selection. Solid lines indicate results of linear regressions with statistically significant slopes at P < 0.05 (see SI Appendix, Table S4 for test statistics).