Briefly, the law of limited competition is this: You may compete to the full extent of your capabilities, but you may not hunt down your competitors or destroy their food or deny them access to food.
Lions and hyenas will kill competitors opportunistically (as will other creatures, like baboons), but the law as stated holds true: they do not HUNT their competitors the way they hunt their prey. That is, they’ll kill a competitor if they come across one (especially in conflict over food when food is scarce), but in the absence of a competitor, they won’t go looking for one to kill. Such behavior would be evolutionarily unstable. (See The Selfish Gene by R. Dawkins.)
As a strategy, it just doesn’t pay off to use your time and energy hunting competitors that you DON’T eat (and that will fight back to the death) instead of using your time and energy to hunt prey that you DO eat. It’s not a matter of ethics, it’s a matter of calories.
