Sexual selection studies have traditionally focused on reproductive competition as a typical male characteristic, and regarded females as largely passive. However, empirical evidence now shows female competition to be widespread in nature. Sometimes the same conventional logic can be used to explain competitiveness in males and females: that the sex in surplus in the mating pool has to compete for the other sex as a limited resource. Still, female competition often does not follow this pattern. This is partly related to the fact that whereas the obvious target of male competition is usually access to mates, in females, competition for mating opportunities is often intertwined with competition for breeding resources. Rather than assuming a rigid dichotomous view of sex roles focusing on which sex is more competitive, the topic may be more rewardingly approached by identifying how ecology affects costs and benefits of competitiveness in the two sexes separately.

Key Concepts:

• Larger mating skew in males than females often leads to stronger sexual selection on male competitive (and attractive) traits.
  
• A switch from a male-biased to a female-biased operational sex ratio may often, but not always, explain reversal of competitive roles.
  
• Female competition is widespread in species with otherwise conventional sex roles.
  
• Female may compete for mates to increase conception probability, to secure the best providers, or to prevent others from reproducing and thereby reduce future resource competition.
  
• Access to resources is more likely to be the ultimate cause of competitive traits in females compared to males.