Sexual size dimorphism in fallow deer (Dama dama): do larger, heavier males gain greater mating success?

Sexual size dimorphism may evolve as a result of both natural and sexual se lection. In polygynous mammals, the main factor resulting in the evolution of large body size in males is the advantage conferred during competition f or mates. In this study, we examined whether sexual selection acts on body size in mature fallow bucks (Dama dama) by examining how the following trai ts are inter-related: age, body (skeletal) size, body mass, prerut dominanc e rank, rut dominance rank and mating success. This is the first study to e xamine how all these factors are together related to the mating success of a large sexually dimorphic and polygynous mammal. We found that male mating success was directly related to body size, but not to body mass. However b ody mass was related to prerut dominance rank which was in turn strongly re lated to rut dominance rank, and thus there was an indirect relationship be tween mating success and body mass. Rut dominance rank was the variable mos t strongly related to mating success. Mating success among mature males was unrelated to age. We conclude that larger mature fallow bucks have advanta ges over other males when competing for matings, and sexual selection there fore continues to act on sexual size dimorphism in this species. Heavier fa llow bucks also have advantages, but these are mediated through the dominan ce ranks attained by males before the rut.