Social and Population Dynamics of Yellow-Bellied Marmots: Results from Long-Term Research

Armitage, Kenneth

Population dynamics is the consequence of the fitness strategies of individuals. Fitness is measured as reproductive success, i.e. the production of descendents. Individuals may forego short-term reproduction to increase survival (51), thereby increasing the incidence of iteroparity and lifetime reproductive success (LRS). Measured as production of offspring, LRS is not a panacea for answering evolutionary questions (64). However, the value of LRS is improved if the reproductive success of descendents is determined. Measuring LRS requires detailed, longitudinal studies of individuals. Such studies allow us to partition and evaluate the significance of various components of LRS, such as age of first reproduction, degree of iteroparity, production and survival of offspring, and recruitment (43). A major component of the fitness strategy of an individual social behavior with conspecifics. Social behavior can affect various components of LRS. Aggressive behavior may reduce fecundity by inhibiting reproduction (1 12). Social behavior affects spacing behavior (82, reviewed in 45) that, in turn, may limit immigration and group size and cause some individuals to disperse (35, 61, 70, 83). Dispersal may be density-independent (62) and is related to mating systems (65, 93). Among mammals in general, juvenile males are the predominant dispersers, especially in those species with promiscuous or polygynous mating systems (48). Generally, male mammals compete for mates, and females compete for resources for rearing young (e.g. 34). Hence, both males and females play key roles in the processes of dispersal and recruitment, especially with individuals of the same sex. Although dispersal should be viewed as a process to increase an individual's fitness (4, 52, 90), dispersal has demographic consequences (84, 102). Finally, social dynamics may be kin-biased (19); therefore, the population consequences of social behavior may depend on the relatedness of the individuals involved.