A Model for Delayed Reproduction in Iteroparous Animals

Abstract

A quantitative model to calculate thresholds for delayed breeding in iteroparous animals with discrete age classes is derived from the Euler-Lotka life-table equation. Four key variables are identified; these are intrinsic rate of increase, risk of attempting to breed as a subadult, adult survival rate, and expected reproductive success of subadults relative to that of adults. Data for yellow-eyed penguins are used to illustrate how the model can be applied to specific cases. The model predicts that delayed breeding is most likely to evolve in long-lived K-selected species. It also predicts that sexual bimaturism is favored in polygamous species when male experience influences ability to obtain mates. Finally, it predicts that delayed breeding is more likely to evolve when the risk of breeding is high for subadults. These predictions are consistent with previous theory and available evidence. The model clarifies the relationships between key variables affecting age of first breeding, facilitates quantitative tests of theory, and allows analyses of the relative importance of various selective factors in specific cases.