It should be obvious from this brief discussion of the biotic aspect of an ecosystem that all organisms play an important role. Any alteration in the number or diversity of the various groups of organisms can have a dramatic effect on the normal function of the ecosystem. Abiotic Factors. The functions of plants and animals in an ecosystem are directly related to interaction with other organisms as well as the physical and chemical environment in which they live. For example, variations in abiotic factors control the reproductive, mortality, and physiological rates and behavioral patterns of the animals. All organisms require moisture to survive. This moisture comes from the environment or other organisms that are consumed. For this reason moisture availability above and below ground in an ecosystem is extremely important to the survival and functioning of both plants and animals. This is especially true in semi- arid and arid regions such as the deserts of the Southwest. Most of the functions of plants and animals are directly influenced by the temperatures of their surroundings. For example, the poikiolotherms (cold blooded animals) maintain the correct body temperature by moving to the proper environment. Rates of physiological function as well as behavioral and distributional processes are also directly correlated with temperature variations. Environmental temperatures are, in turn, a result of many other abiotic factors. For example, soil temperatures are influenced by soil moisture, soil color, wind movement over the soil surface and shading or sun exposure. Air temperatures at any one location are also a result of many of these same factors, i.e., amount of solar insolation, air movement, humidity, etc. Moisture and temperature are probably the two most critical abiotic environmental factors in controlling the functions and diversity of plants and animals. They are obviously closely interrelated with other factors. Some have been mentioned such as solar radiation, air movement and soil type, but other factors can also be important. These factors can be characteristic of a particular habitat. Topographic and geological features, for example, influence the amounts of solar radiation soil moisture retention and potential nutrients in the soil. The interaction of all of these factors as well as many others that are difficult to measure produce the interwoven aspect of the environmental complex. They can be separately studied but
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