Figure 2.

(a) Coevolutionary dynamics for investment in discrimination ability d and investment in amplifying cues used in discrimination, v. Red arrows are eight particular directional selection gradients scattered evenly throughout the phase portrait; the stream flow-lines are the evolutionary trajectories starting at any given population values of d and v. The lengths of selection gradients measure vector-sum strengths of selection and consequently are proportional to the speed of joint changes in d and v. Values of discrimination parameters: difficulty of discrimination a = 0.80, benefit of discrimination b = 8. Blue dots are stable equilibria. (a) The efficiency of discrimination, e = 0.20, is less than the efficiency of cue diversity amplification, f = 0.40. (b) The efficiency of discrimination, e = 0.40, is greater than the efficiency of cue diversity amplification, f = 0.20. A higher efficiency of discrimination (lower e) moves the discrimination system to a stable equilibrium of higher discrimination ability and lower cue diversity exaggeration, and vice versa. The strength of selection and the speed of progress to the equilibrium are still higher farther from the equilibrium and for lower starting values of d* and v* in regions where selection moves the population towards the non-trivial equilibrium. (Online version in colour.)