ABSTRACT
By way of introduction let us provide a concise description of the conditions and patterns of life in an environment to which the models developed in this chapter apply.
The two necessities of pastoral activity are pasturage and water. Their spatial distribution tends to be uneven and is largely influenced by seasonal changes in the weather. Hence, in an attempt to maximize the input of these two resources nomadic movements must be made. Moreover, the nature of pasturage and the distribution of watering points determine the composition of herds. Dietary needs differ between the various species of animals. At one extreme, cattle subsist mainly on grass and require frequent watering, thus being confined to grasslands over which watering points are adequately distributed. At the other extreme, camels need to browse and seldom to graze. Also, they have to be watered at much less frequent intervals than other herding animals. Sheep and goats live on both grass and leafage of trees as well as bushes. These factors are responsible for the way in which the herds are split into groups according to the type of animal. It may also be noted that the size of a group influences the frequency of its movements: the bigger the herd the more quickly will local supply of feed be exhausted.
