Fitness costs of gestation and lactation in wild mammals.

Like a number of plants, some mammals commonly produce more progeny than they can afford to rear, terminating investment in some or even all of their offspring once the resources available for breeding are known. Adaptive interpretations of juvenile wastage rely on the argument that the costs of gestation are small compared to those of feeding offspring. Though energetic evidence supports this conclusion, it is unsafe to assume that the relative costs of gestation and lactation to the mother's survival and future reproductive success follow the same pattern because lactation commonly coincides with the period of maximum food availability. Controlling for individual variation, we show that in wild red deer (Cervus elaphus L) any costs of gestation to the mother's subsequent survival and reproductive success are slight compared to those of lactation.