Delayed Competitive Breeding in Roving Males

In several species of large mammal, males rove during the mating season, searching for receptive females. In these species, males show considerable sexual dimorphism, and remarkably long delays between sexual maturity and effective competitive breeding. Evolutionarily stable strategies were sought for a model of this breeding system in which large males outcompete smaller males and competitive breeding inhibits growth or survival. The model predicts that roving males should delay competitive breeding until attaining a size at which there are less than a mean of about two to four larger males attending each receptive female. In species in which there are long intervals between the oestrous periods of females, but each can potentially be attended by a number of males, then delayed competitive breeding will be particularly favoured. The conclusions of the model seem consistent with available results on African elephants, sperm whales and polar bears.