Evolution of unstable and stable biparental care

Evolutionarily stable strategy models suggest that biparental care will be stable when parents partially compensate for changes in care by the other parent Previous work has emphasized the relationship between parental expenditure and the current component of fitness (e.g., offspring survival and fecundity) in causing partial compensation. This study shows that partial compensation depends critically on the effect of current parental expenditure on a parent's future fitness (e.g., survival to and fecundity in subsequent breeding seasons). Partial compensation is favored and biparental care is stable when future fitness is a concave-down function of expenditure (i.e., each increment of expenditure is more costly than the previous). However, when future fitness is a convex-down function of expenditure (i.e., each increment of expenditure is less costly) biparental care is unstable. Key words: evolutionarily stable strategy, fitness, fecundity, parental care, parental expenditure. [Behav Ecol 7:490-49