I base my opinion on the antics of the foxes fighting outside my window right now. I am fairly sure I won't find a dead fox on my doorstep in the morning and I am fairly sure tomorrow will be another chapter in the on-going duel. Their fighting is truly no-holds barred however killing is not necessary to win females/territory. A given territory only supports a given quantity of a given species, a given territory can only be defended up to a certain area, so there is no concern needed to only fight so far lest the population/gene pool be diminished.
As for us humans and how we fight, we are pack animals that can augment our fights with words. This applies okay in pub brawl situations, however, we have no hesitation at all when it comes to wiping out rival tribes. This has applied historically, I think that Hitler bloke was quite keen on wiping out the Jewish tribe and, although worded differently, Bush and Blair had no qualms when it came to wiping out tribes of people in more recent times. We also have class hierarchy so the rich have no problems sending millions of their own off to certain death, e.g. WW1, because they are a different tribe within a tribe. Concern for population depletion really matters not.