The perfect family: A re-examination of biparental care in animals

Current theory of parental care holds that parental care patterns result from conflicts of interest between parents. One prediction from the current theory is that in species with biparental care, parents should compensate only partially for a reduction in their partners' effort. This prediction has been tested in birds, but the results are equivocal. Here, we present a different model within the framework of social selection theory that does not assume conflicts of interest between parents. In this model, both parents cooperate to maximize the number of offspring produced from the current clutch; hence the "perfect family". Successful reproduction requires two different tasks, e.g. nest defense and nestling provisioning. Parents have set time budgets that they must allocate between the different tasks to maximize offspring produced from the nest. Given this setup, we show how time allocation changes when one parent is manipulated and derive the conditions for when partial or complete compensation responses for provisioning rates are expected. Our results show that available empirical data can be explained with a model that does not presuppose a conflict of interest between parents. Thus, this work presents a null model against which assumptions of conflict can be compared and tested. Finally, we discuss the implications for future empirical studies, stressing the need for collecting data on time allocation between different components of parental care.