Provisioning under the risk of starvation

Providing for altricial young can be risky. Fundamental to understanding the risks involved, along with their management, is the trade-off between current and future reproductive effort. Here we present a dynamic model of provisioning under an important source of risk: starvation. Given the choice of foraging or provisioning at each point in the provisioning period, we show that, when parents have a higher risk of running an energy deficit while foraging, offspring have a poorer chance of surviving to independence. Unexpectedly, our results also predict that, for low to moderate levels of such risk, surviving offspring are likely to show improved condition than if energy intake was more certain; by buffering themselves from the risk of starvation, parents put offspring at risk while ending up with more resources to invest in survivors. As the value of ensuring parental survival decreases, this effect becomes less pronounced and provisioning declines. Thus, a component of reproductive effort can decline with age or increase with longevity in response to a common source of biological risk. These results show that environmental variability can have effects on the evolution of provisioning for altricial young that do not follow from traditional life-history reasoning.