Mating system and reproductive success: a comparison of two African forest monkeys (Colobus badius and Cercopithecus ascanius)

The folivorous red colobus lived in patrilineal, multi-male groups, whereas the omnivorous, redtail had matrilineal groups usually with only one adult male, but occasionally experiencing temporary multi-male influxes. In red colobus, offspring survival was positively correlated with interbirth interval. Among the primate species examined, females invested more in their sons and daughters depending upon variables such as intersexual differences in variance in reproductive success, the dispersing sex, and maternal dominance rank as it influenced the offspring's reproductive success. Lifetime reproductive success (LRS) of female red colobus was influenced most by offspring survivorship and less so by birth rate. LRS of male red colobus was largely a function of reproductive rate and lifespan. Although offspring mortality and reproductive lifespan were nearly identical for males of the two species, the harem breeding system and highly skewed adult sex ratio lead to greater, more variable LRS in redtail males. Male red colobus within groups produced c20% more offspring per year than male redtails, but the large proportion of red colobus males with zero breeding success reduced mean LRS to 40% less than redtails. Annual fecundity among adult females of both species was similar; variance in annual fecundity among female redtails was over five times greater than in female red colobus. Although females are the primary dispersers in red colobus, they did not have a greater coefficient of variation in LRS than in species where females rarely disperse, because they were readily accepted into new groups and their intergroup transfer was relatively rapid. In both species, adult males contributed, on average, more offspring to the succeeding generation than adult females, as in other polygynous mammals, because fewer males survived to adulthood, but once they reached adulthood, their reproductive lifespans were similar to females. -from Authors

Duke Scholars

Author Thomas T Struhsaker Evolutionary Anthropology