The risks of parenthood. I. General theory and applications

Summary We use contemporary life history theory to analyze parental decisions concerned with the defense of offspring, and with the provisioning of offspring in the presence of risk. In achieving the optimal level of parental investment, the parent faces a tradeoff between present and future reproductive success. Our models, which are based on stochastic dynamic programming, lead to predictions of the following kind: (i) offspring will be defended more vigorously as they grow older; (ii) long-lived species will accept fewer risks in caring for offspring than short-lived species; (iii) parents living in permanently riskier environments will defend their offspring more vigorously than parents in less risky environments; (iv) however, temporary increases in risk will result in temporarily less vigorous defense and provisioning of offspring. The models also show that parents and their offspring have different conceptions of the optimal level of parental investment. The flexibility of our modeling approach as a method of analyzing facultative behavior is also emphasized. Finally, we apply the methods of this paper to analyze fledging behavior of Atlantic puffins.