3-3.1.3~~3-3.2.1

Each population in an ecosystem has a range of tolerance to variations in its physical and chemical environment , as shown in figure 3-9.Individuals within a population may also have slightly different tolerance ranges for temperature or other factors because of small differences in genetic makeup , health , and age.For example, a trout population may do best within a narrow band of temperatures(optimum level or range), but a few individuals can survive above and below that band. Of course , if the water becomes much too hot or too cold, none of the trout can survive.
A variety of abiotic factors can affect the number of organisms in a population. Sometimes one or more factors, known as limiting factors, are more important in regulating population growth than other factors. This ecological principle is called the limiting factor principle:too much or too little of any abiotic factor can limit or prevent growth of a population, even if all other factors are at or near the optimal range of tolerance. This principle describes one way in which population control-a scientific principle of sustainability(Figure 1-13,p.20 and back cover,and Concept 1-6,p.19)-is achieved.
每個族群在生態系中對物理和化學環境的忍耐程度有所差異，族群中個體對溫度或其他因素的容忍程度稍微不同，因為基因、健康和年齡的差異.
各種非生物因素可能影響生物族群.有時候，一個或多個因素被稱為限制因素，控制族群增長比其他因素更為重要，這個生態原則被稱為限制因素原則:過多或過少的任何非生物因子可以限制或阻止族群增長，即使所有其他因素都達到或接近最佳容忍範圍，這原則描述一種控制數量的方法.