The reproductive consequences of infanticide in langurs: A mathematical model

Summary

• 1. An analysis of the factors influencing the reproductive success of infanticidal and noninfanticidal adult males in populations of langur monkeys (Genus Presbytis) is presented. Male tenure, defined as an adult male's length of residency in a one-male bisexual group, is demonstrated to be an important factor in any reproductive advantage accruing to infanticidal males. Other factors include the lengths of the female interconception intervals, the time at which adult male replacement occurs relative to the start of any such interval, and whether or not the subsequent replacement male is also infanticidal.

• 2. Infanticide is found always to confer a reproductive advantage on the resident male in a bisexual group under conditions of subsequent replacement by a noninfanticidal male. Infanticide would thus be expected to spread when introduced into an otherwise noninfanticidal population. Under conditions of subsequent replacement by an infanticidal male, infanticide is found to be advantageous for the resident male only a particular lengths of tenure. Infanticide would thus become fixed only in populations where the distribution of tenure lengths is advantageous for infanticidal males. Accordingly, it is predicted that average or modal tenure length in populations fixed for infanticide should coincide with those tenure lengths theoretically yielding a reproductive advantage for infanticidal males. Three direct estimates of average male tenure obtained from field studies of langur populations are consistent with the predictions of the model.