Between-individual differences in behavioural plasticity within populations: causes and consequences

Behavioural traits are characterized by their labile expression: behavioural responses can, in principle, be up- and down-regulated in response to moment-to-moment changes in environmental conditions. Evidence is accumulating that individuals from the same population differ in the degree and extent of this form of phenotypic plasticity. We here discuss how such between-individual differences in behavioural plasticity can result from additive and interactive effects of genetic make-up and past environmental conditions, and under which conditions natural selection might favour this form of between-individual variation. We highlight how spatial or temporal variation in the environment, in combination with competition among individuals, can promote adaptive individual differences in plasticity; and we detail how differences in plasticity can emerge as a result of selection pressures induced by social interactions or as a response to between-individual differences in state. We further discuss both ecological and evolutionary consequences of individual differences in plasticity. We outline, for example, how individual differences in plasticity can have knock-on effects on the rate of evolution; and how such differences can enhance the stability and persistence of populations.