Give an example. In lecture I pointed out that traits selected by intrasexual competition are likely to be sexually dimorphic. For example, males should be larger, and have bigger weapons, than females, if males compete with each other to gain mates. Both sexes use their horns to defend against predators. In the fall breeding season, males fight for females by butting heads and crashing horns.
Winners mate with multiple females and losers fail to mate.
In white-tailed deer, only males have antlers, and they have them only in the mating season. Males fight for females by locking antlers and shoving. Like mountain-goat males, winning male dear mate with multiple females and losers don't mate. Unlike mountain goats, male deer shed their antlers in the winter as soon as the mating season is over. Antlers regrow in summer and are fully grown by the fall mating season.