Fig. 3.

Evolved migratory strategies under different ecological conditions. (A) The proportion of leaders in, and (B) the migratory ability of, evolved populations as a function of density (ρ), and cost of gradient detection (p_g). Note that density is measured in units of individuals per BL⁻². Population migratory ability is defined as the migratory benefits averaged over all individuals in the population. (A) There is a clearly demarcated individual-migration state (bright region), a collective-migration state (yellow-red regions), and a no-migration state (dark region) with sharp changes in the proportion of leaders between these evolved migratory states. (B) Corresponding changes in population migratory ability is relatively gradual. The density is on a log-axis covering nearly five orders of magnitude and the collective migration state occurs for densities where the interactions between individuals are very rare. Parameters: N = 320, p_s = 1.0, and σ_r = 0.10. The other parameter values are in SI Appendix A.