Personality predicts decision making only when information is unreliable

Phenotypic plasticity in decision making should be selected for when reliable information on current conditions is available. When current information is unreliable, however, selection should favour unresponsive behavioural phenotypes, which might lead to the emergence of personalities. We tested the hypothesis that personality will affect decision making when information is unreliable, but not when it is reliable. We measured two personality traits, boldness and anxiety, in 55 wild chacma baboons, Papio ursinus, by quantifying responses to a novel food and a mild threat, respectively, in repeated field experiments. To assess decision making under different information reliabilities, we recorded foraging decisions in two contexts. We followed the baboons as they foraged naturally with reliable information about their environment (>8900 decisions) and, to manipulate information reliability experimentally, we performed a large-scale in situ foraging experiment during which we provided the study troops with access to experimental food patches (>10 000 decisions). Importantly, the baboons could not see the food in the experimental patches until close inspection of them, and thus had unreliable information about patch quality. We found plastic foraging decisions in the presence of reliable cues, but personality-dependent decisions in the absence of such cues. Specifically, bold individuals were more likely to produce, and shy individuals scrounge, in the experimental arena but there was no effect of personality on foraging decisions under natural foraging conditions. Our results clarify the importance of information reliability in the evolution of personality and plasticity. These findings also contribute to our understanding of how individuals, and thus populations, might respond to environmental change in the future.