Animal Competition and Aggression
Dogs are mans best friend. But believe it or not they do act aggressively in different ways. To their owner they will not show any aggression but if they meet a stranger they may bark, bare teeth, snarl/growl and other things because they dont know the person. When dogs pee it is because they are marking territory and saying "this is mine." This is an example of competition between dogs.
Rams are another animal always in competition with each other. They butt heads to see which ram is stronger and to decide leaders. Rams have died from this type of competition.
Sheep and Kangaroo
In Australia there is a competition between kangaroos and sheep. The competition is between food. The sheep usually have the advantage in this one though. Not only does the Kangaroo have to fend off the sheep but the farmers as well so it is quite difficult for the kangaroos.
Lions vs. Hyenas
In Africa there is a competition for resources. It is between lions and hyenas. Although lions are much stronger and larger than hyenas, The hyenas have the advantage because they travel in much larger packs than the lions do. They compete for food and water both. When they encounter each other it usually ends in death for some.