Supplemental feeding reduces natural selection in juvenile red deer

In red deer, variation in winter and spring weather conditions encountered by the mothers during pregnancy and during the first year of life are a main determinant for individual life‐history as well as population dynamics. We tested the hypothesis that supplementary feeding which provides constant food supply throughout winter removes the selective pressure of winter harshness on nutrition‐mediated phenotypic traits. We analysed cohort variation in body weight in calves in October, before their first winter, and in yearlings in June, after their first winter, in a food‐supplemented population in the Eastern Austrian Alps. Over eleven years, cohort body weight varied between years in calves and yearlings. Contrary to studies on non‐supplemented red deer populations we found neither short‐ nor long‐term effects of winter weather on body weight. In calves, autumn body weight was negatively related to April–May and June temperatures, suggesting that cool weather during the main growth period retarded plant senescence and thereby prolonged the period of high protein content of summer forage. In yearlings, variation in June body weight, shortly after the end of the feeding period, was lower after a wet April–May, suggesting a negative effect of a prolonged period of supplemental feeding. For both calves and yearlings intra‐cohort variation in body weight was higher, inter‐cohort variation was lower as compared to non‐supplemented red deer, suggesting that in their first year of life supplemented red deer are under reduced natural selection pressure.