Reproductive cost in female European and mountain hares

AbstractIn female mammals, reproduction requires high‐energy expenditure because of gestation and lactation; therefore, a fitness cost of current reproduction may lead to a decrease in future survival or reproduction. The reproductive cost differs between short‐lived species with a fast life history strategy compared to long‐lived species with a slow life history strategy. We used harvest data on reproduction and body mass from two small‐sized and short‐lived mammals, mountain and European hare (Lepus timidus and Lepus europaeus) to explore the cost of reproduction and determine how the number of newborns produced in the current breeding season affects female body mass at the end of the reproductive season. Within a reproductive season, female hares experienced a reproductive cost: current litter size was negatively affected by the number of newborns produced in the current breeding season until the current litter. In the given reproductive season, females that had had more litters also had the highest reproductive output and had higher body mass at the end of the breeding season. The presence of a reproductive cost and the high reproductive performance of heavier female hares suggest a strategy of reproduction more conservative than expected for a species with a relatively small size and fast life history strategy. Heavier female hares seemed to be able to face the cost of reproduction, produce more offspring and remain larger at the end of the reproductive season: a strategy that is more conservative than risky. We believe female hares adopt, at least in part, a conservative strategy of reproduction characterized by an increased number of litters per season because of the positive fitness payoff gained.