AN OFFSPRING-DEFENSE HYPOTHESIS FOR TERRITORIALITY IN FEMALE MAMMALS

Female territoriality (defined here as defense of exclusive space with respect to conspecific females) among mammals typically has been cons idered a mechanism to defend food resources. We propose an alternative hypothesis that the primary function of territoriality in solitary an d semi-social female mammals is to protect vulnerable young from infan ticidal conspecific females. Female territoriality is prominent among rodents, carnivores, insectivores, and some lagomorphs, but occurs rar ely in bats, ungulates, marine mammals, marsupials, and most primates. A common trait of species with female territoriality is that they hav e nonmobile altricial young that are deposited in a burrow or protecte d den site. In contrast, female territoriality does not occur in speci es with precocial young or species with altricial young that are carri ed with the mother or that are reared communally. The timing of female aggression and territoriality appears to be more closely associated w ith lactation than with food habits or the distribution and abundance of food. Hence, we hypothesize that vulnerability of altricial young t o infanticide, is a pervasive factor in the evolution of territorialit y in female mammals. Territoriality for defense of food appears to be relatively uncommon and restricted to those situations in which food i s centrally located or can be stored in a defensible cache.