A structural-equations model for the mating behaviour of bucks in a lek of fallow deer

In many studies, the causal factors of male copulatory success in leks cannot be experimentally analysed under natural conditions. Information is based on the analysis of correlation and on multiple regression models. However, these methods are often flawed or unsuitable for conclusive results. By contrast, an explicit model of the breeding behaviour of male fallow deer (Dama dama L.) has been formulated using structural (regression) equations. The model describes with outstanding precision the network of short-term determinants of male copulatory success. Harem size is identified as the most important indirect cause of male copulatory success and, in its turn, it is a function of (i) lek attendance, (ii) intensity of herding, (iii) aggressive behaviour towards other bucks and (iv) courtship. Comparing the results of the structural-equations model with those of a partial correlation analysis and of a multiple regression study, we conclude that the statistical method presented here better describes the complexity of the causal web which characterizes leks than other statistical methods commonly used in these studies.