they must be analyzed in relation to the complexity of the ecosystem. Ecosystem Cycles. Each function or response of a plant or animal in relation to abiotic factors is not totally separate from the responses of other organisms or other factors. All processes within an ecosystem are, in some way, related and cyclic in nature. For example, solar energy flows in from outside the earth’s atmosphere, is transformed into different physical or biochemical forms and through various conversions is ultimately lost again as heat to outerspace. The rate of flow of the energy through these cycles controls the physiological and growth processes of the organisms as well as many abiotic factors such as evaporation, temperature and air movement. Although energy and the energy cycle are driving forces in the ecosystem, other cycles are of great enough significance to be considered in research on ecosystem responses. In the arid regions the water or hydrological cycle is of great importance. In this cycle both physical and biological factors play an important role. For example, air temperature controls the amount of moisture in the air and the potential for precipitation as well as evaporation; soil texture and structure control the amount of water maintained by the system while plants intercept precipitation, control runoff and remove quantities of water from the system through transpiration. The water cycle can thus be considered the flow of water from a physical state through a biological function and back into a physical state with all facets of the ecosystem acting on the processes. Other cycles such as the nitrogen or carbon cycle are important to proper functioning of an ecosystem but they are closely related to energy and water flows. It should be obvious that an understanding of ecosystem response to perturbation such as construction and operation of solar collectors is not dependent on analysis of the response of a single animal or plant species or a single physical factor but requires a study of those factors that most significantly influence biotic functions and an analysis of the accompanying biotic changes. These changes occur most often as changes in animal and plant species composition (diversity) as well as species density. These two measurements are indicators of the organisms ability to grow and function within its original or newly created environment.
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