定義： A plain without trees (apart from those near rivers and lakes); it is similar to a prairie, although a prairie is generally considered as being dominated by tall grasses, while short grasses are said to be normal in the steppe. It may be semi-desert, or covered with grass or shrubs or both, depending on the season and latitude.
定義： An interaction relationship involving a predation process, where the subject kills the target in order to eat it or to feed to siblings, offspring or group members
