A brown anole, boasting. That's a pouch, not a slice of orange.
Most animals don't bother to defend a territory. They don't need to. Of those that do, most do so by marking their boundaries (a rhino's heap of scented poo can reach a metre high and five metres across).
A few animals engage in some sort of boasting to maintain their territories. They might try to make themselves look bigger by puffing themselves up, or they may sing (as cats do). Ring-tailed lemurs have "stink fights" which involve getting their tails as smelly as possible and waving them at animals in the next territory.
Some animals (red squirrels, badgers, beavers) bother less about their neighbours than complete strangers; a few animals (striped mice, weaver ants) are more bothered by their neighbours than strangers.
Sometimes, rarely, some types of animal will fight over territory. This is plainly very foolish indeed as it makes everybody concerned less likely to survive.
Luckily most creatures have long-ago worked this out.
Not quite all of them, though.
Thing Not To Do Today: be territorial. This word comes from the Latin territōrium, which means land surrounding a town.