Imagine a food resource spread out uniformly across a landscape—grass, if you're a grazer, extending as far as the eye can see. As a male, where would you stand guard? Even if it were absolutely necessary for females to visit places with grass to feed, and even if they were willing to mate with you if you happened to be there when they fed, where would that location be? For food resources broadly distributed in space, there is no obvious location that is better than any other. It would be impossible for a male to anticipate where females were likely to visit since they could find their food anywhere. A male could still invest in the production of weapons, and he could use his weapons to deflect rivals from a patch of turf. But why should he bother to guard one particular area if all of the surrounding areas are just as good? And why should he pay the price of producing a weapon and fighting, if other males without weapons or territories do just as well as he does? In the parlance of economists, such behavior would not be cost-effective.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 201