10 - Environmental Factors and Growth

To understand how the many environmental factors influence growth, the basic rate functions should never be lost sight of, despite the general simplicity of growth measurements. As far as possible, the individual functions have been introduced in the chapter to provide some explanation of the response to environmental factors, without deviating from the major purpose of examining the recorded trends in the activity of growing. In relation to environmental effects, quite obviously growth cannot be studied without involving food consumption, even though the latter may not necessarily be measured. In this respect, growing—unlike such activities as swimming or respiring—is inseparably coupled with a powerful biotic factor, so that any abiotic factor is necessarily involved in some form of interaction between the two. Growth rate may either increase or decrease depending on the nature of the food × metabolism × temperature relation; on analysis it can be seen that the energy demand of elevated metabolic rate could have exceeded the gain from increased food uptake resulting in reduced growth rate. Furthermore, the act of growing necessarily alters size so that another important biotic factor continually changes with time. An understanding of these inherent involvements is necessary before any clear insight of the environmental relation to the growth process can be achieved.