Risk sensitivity revisited: from individuals to populations

Risk-sensitive foraging theory is central to behavioural ecology. It relates individual fitness to variance in foraging success (risk) and predicts which foraging strategy maximizes fitness under applicable constraints. Fitness usually comprises survival and reproduction. Yet, most models of risk-sensitive foraging have focused on only one of these two factors. Consequently, such models cannot account for the interaction between resource availability and population size, i.e. density dependence.Here, we incorporate both mortality and reproduction as functions of an individual’s risk-sensitive foraging strategy. In our model the individual strategy thus determines the mean availability of resources per capita and consequently the equilibrium population size. From a continuum of possible strategies we are able to pinpoint the exact risk-sensitive strategies that are favoured by natural selection in saturated habitats and demonstrate that, in addition to risk proneness and risk aversion, a number of optimal intermediate variances can be selected for.In contrast to predictions based on models that ignore the interaction between behaviour, population density and resource availability, our results show that high baseline mortality (e.g. predation risk) does not necessarily lead to risk proneness. In addition to this novel finding, our model confirms the crucial importance of resource-independent (baseline) mortality for optimal risk-sensitive behaviour.

► Influence of behaviour on density alters predicted risk-sensitive behaviour.
► High resource-independent mortality does not necessarily favour risk proneness.
► Resource-dependent mortality and natality explain risk-intermediate behaviour.