Introduction

The family Canidae is unusual among mammals in that its pervasive mating system is obligatory monogamy (Kleiman 1977). Canids have large litter sizes and a long period of infant dependency (Kleiman & Eisenberg 1973). They also characteristically have a high degree of (1) intraspecific flexibility in social organization, and (2) cooperative behavior within social groups, ranging from hunting and food sharing to the provisioning of sick adults and dependent pups (Macdonald & Moehlman 1983; Moehlman 1989). In this chapter, we use an up-to-date and expanded data set to conduct a review of canid life-history traits and ask how body mass, resources, and behavior interact to facilitate the development of cooperative breeding. We pursue two lines of inquiry. We first discuss the influence of body mass on life-history traits and test hypotheses that consider ecological and behavioral correlates of reproductive output. We then consider the costs and benefits of alloparental care in greater detail and ask how the evolution of reproductive suppression is related to individual reproductive tactics.

Previous analyses of the allometric scaling of life-history traits in canids revealed positive and significant relationships between female body mass, gestation, neonate mass, litter size, and litter mass, which appeared to be linked to breeding behavior in a systematic fashion. These relationships suggested that larger canids might require helpers for the successful rearing of young (Moehlman 1986, 1989). In carnivores, cooperatively breeding and biparental species have a higher litter mass than species with strictly maternal care (Gittleman 1985a, 1986).