The system as a whole operates in an irregular pulse-reserve pattern. No cycles have been demonstrated. The main adaptational problem, therefore, lies in the adjustment of response to exogenous environmental signals so as to optimise growth and survival. All animals have the added problem of heat and salt balance coupled with water balance in the typically extreme desert temperatures, but they also have the advantage of mobility which allows them to exploit spatial variation. In some special cases, the use of available water is inhibited by special conditions, such as very cold winters in Central Asia.
Survival is generally by means of reserves.
The nature of these reserves constitutes the most significant field for research. In this characterization of arid ecosystems based on the current state of knowledge there is an abundance of ideas for the formulation of hypotheses about the organization of human activity in arid areas, and such hypotheses can be used without imposing an ecosystemic framework on human activity. For example, in human populations in arid lands a similar pulse-reserve pattern may be seen. Most traditional systems of food production are adapted in this way. Nomadic pastoralism is a good example.