Once the lead bull establishes a territory, he will scare off any challengers that threaten his authority over his home or his group. When a hippo yawns, it actually may be showing off enlarged canines to frighten a trespasser. Males ram each other with their mouths open, using their huge heads like sledgehammers and their big mouths as buckets to throw water at each other. On land, hippos clear trails through vegetation which allow other animals easy access to water. This keeps these grasses well trimmed, which stimulates new growth and discourages takeover by shrubs and trees.
Hippos spend most of their days in the water, where they defecate in substantial amounts.
Their dung enriches the water with essential elements for a very important food chain that begins with a multitude of microorganisms. The microorganisms are eaten by fish which in turn are eaten by larger fish, aquatic reptiles, and birds. Native people also benefit when fishing, hunting, and traveling the trails and waterways. Originally, hippopotami ranged throughout the continents of Asia, Europe, and Africa. Over the past several hundred years, even their remaining African range has decreased.