Territorial defense is when the animal is protecting there territory if then sense a threat. So what the animals do is they leave there sense, like pee or something around there territory. So when other animals are passing a tree or something they may smell pee. Without marking your territory you do not have a place to defend which may make them look weak. When the animal smell pee they either back off or enter the territory, which if they do there will be some consequences.
I learned about suckling and that most baby mammals suck to get their milk. Without their milk they do not have anything in their stomach. When we humans were all babies we had to suck our moms breast to get the food we need. Without our mother I don't know what other baby mammals would do.