Effects of predation risk on the body mass regulation of growing wood mice.

Body mass in wild animals has been suggested to be regulated by the opposing fitness consequences of variation in body size (and fat storage) for starvation and predation risk. Many studies of adult mammals and birds have broadly confirmed the predictions of this model. However, relatively few studies have addressed the potential role of such trade‐offs during early phases of development when animals are growing. Similarly, studies of the impact of high‐fat diets on wild small mammals generally show a resistance to weight gain. But whether growing animals are similarly resistant is unclear. In this study, weaned wood mice (Apodemus sylvaticus) were exposed to a high risk of predation, simulated by the broadcasting of owl calls, for 66 days during which body mass and energy intake were monitored. We hypothesized that if the risk of predation plays a role in regulating body mass during this phase then animals growing under predation risk would grow less. We found female (but not male) mice exposed to the predation risk treatment had lower growth rates and ended the experiment lighter; however, variations in energy intake and resting metabolic rate did not explain the observed differences. Feeding on high‐fat diet resulted in individuals with higher body mass. Females reached their adult size earlier than males and were more responsive to the predation risk treatment when feeding on high‐fat diet. Our data suggest males body mass to have fitness consequences on social dominance and reproductive success not accounted for in the simple starvation‐predation trade‐off model. [ABSTRACT FROM AUTHOR]