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. 2018 Jun 20;285(1881):20180180. doi: 10.1098/rspb.2018.0180

Figure 2.

Figure 2.

Illustrative graphing of dangerous risk-taking by two classes (male: blue; female: pink) in: (a) a weakly polygynous system; and (b) a highly polygynous system. In both systems, males and females both have a 50% chance of succeeding at the risk (p♂ = p♀ = 0.5) and have zero fitness if they fail (Ef,♂ = Ef,♀ = 0). In both systems, a female's payoff without risk is somewhat affected by her state (En,♀ = 2 + 4x, dotted pink line); her maximum fitness is 6, obtainable either from being in the best possible state (x = 1) or from taking a successful risk (Es,♀ = 6). Correspondingly, dangerous risk-taking is only worth it for the bottom 25% of females (pink shaded area) in both systems. Male payoffs are more variable than female payoffs, but to different degrees in the different systems. (a) In the weakly polygynous system, the maximum male fitness (6.5) and the benefits of a successful risk (Es,♂ = 6.5) are slightly higher than for females, and one's state affects the non-risky payoff for males (En,♂ = 0.5 + 6x, dotted blue line) slightly more than females. Correspondingly, slightly more males than females have little to lose and something to gain—approximately 46% of males take dangerous risks (blue shaded area). (b) In the highly polygynous system, the maximum male fitness (8) and benefits of successful risk-taking (Es,♂ = 8) are even higher, and one's state strongly affects the non-risky payoff for males such that males in poor state do not reproduce but males in very good state have disproportionately high fitness (En,♂ = 0 + 8x6, dotted blue line). Correspondingly, many males have little to lose and much to gain from taking dangerous risks, so almost 89% of males do so (blue shaded area). Intensifying the polygyny will exacerbate these sex differences further. In addition to examining sex differences, our state-dependent risk-taking model can be applied to any two (or more) classes, to predict what proportion of each class will take risks, and how this depends on the payoffs for risky and non-risky options in each class.