ABSTRACT
Most of the Earth’s once natural ecosystems have been either destroyed or radically changed by man. Several kinds of ecological interactions may take place across the sharp boundary between the natural desert ecosystem and the human oasis ecosystem. For instance, the people and domestic animals of the settlement may endanger the sparse plant and animal populations of the surrounding desert by grazing, gathering, and hunting. Solid and liquid wastes discharged from the settlement into the desert may have similar biological effects, since they are an additional source of food and water for desert animals. In some cases, of course, they may permit animals to survive without at the same time damaging the oasis ecosystem, but in other cases they disrupt the normal mechanisms of population regulation. The paramount threat to deserts is overgrazing, which is the tendency of local human populations to permit animals to graze freely, without regard to the carrying capacity of range or pasture.
