Tradeoff between offspring mass and subsequent reproduction in a highly iteroparous mammal

Abstract

When resources are limited, current maternal investment should reduce subsequent reproductive success or survival. We used longitudinal data on marked mountain goats Oreamnos americanus to assess if offspring mass at weaning affected maternal survival and future reproduction. Offspring mass was positively correlated with survival of old mothers, suggesting that mothers produced lighter kids, and hence reduced reproductive effort, in their last reproduction. Offspring mass at weaning did not affect survival of young and prime-aged mothers, but females that had weaned heavy offspring had a reduced probability of subsequent reproduction in years of low population density. Because offspring survival is correlated with weaning mass, mothers’ allocation to reproduction involves a tradeoff between current and future fitness returns. We demonstrate for the first time that allocation to current offspring mass in an iteroparous mammal reduces the probability of subsequent reproduction.