Female aggregation interacts with population structure to influence the degree of polygyny in red deer

In polygynous systems, female aggregation may affect the degree of polygyny by increasing the variance in male mating success. However, other population features such as the sex ratio and the age structure of males may also affect the distribution of male mating success. We combined behavioural observations and genetic data to investigate the relationship between spatial distribution, population structure and degree of polygyny in 30 red deer, Cervus elaphus, populations in Spain. We found that although female aggregation was positively related to mean harem size, under conditions of high female aggregation males were unable to monopolize whole female groups. The relationships between female aggregation and behavioural estimates of the variance in male mating success were strongly influenced by the sex ratio and the proportion of competitive males in the population. Potential skew of male mating success and potential opportunity for sexual selection were higher in adults than in young or subadult males. Finally, the behaviourally estimated distribution of male mating success matched the genetically estimated degree of polygyny, especially under conditions of relatively high synchrony in female receptivity. Our results show how population structure can interact with female aggregation in space and time to influence the opportunity for sexual selection in red deer.

► We study the relationship between population structure and polygyny in red deer.
► The relationship between female aggregation and polygyny depended on population structure.
► Opportunity for sexual selection was higher in adult than in subadult or young males.
► Behavioural estimates of polygyny matched with genetic measures under rut synchrony.