Sex-specific predation on a monogamous rat, Hypogeomys antimena (Muridae: Nesomyinae)

Sex-specific predation on adult individuals is often predicted by different behaviour in males and females resulting from different reproductive strategies and social systems. High predation pressure and the need for biparental care are considered a possible ecological basis for the evolution of monogamy, the most puzzling social system in mammals. In species where adults and offspring are vulnerable to the same predators, males and females may protect their offspring to different extents because of conflicting demands of investment in current and future offspring. I present the first empirical data on age- and sex-specific predation pressure by top predators on a monogamous rodent and the sex-specific behavioural responses of the prey species to different rates of predation. During an annual predation peak, only offspring and adult males were killed but no females. Whereas males and females travelled similar distances at night before the period of high predation on offspring, males moved further during this period. At the same time, males and females increased their distance from their offspring but males stayed closer to them than females. As a consequence, the distance between the members of the pair increased during the predation peak. The males' behaviour could lead to their encountering predators more frequently which would reduce survival prospects. The different behaviour of males and females provides empirical evidence that males invest in the welfare of current offspring at the cost of higher predation risk whereas females protect their residual reproductive value. Copyright 2000 The Association for the Study of Animal Behaviour.