tailieunhanh - From Individuals to Ecosystems 4th Edition - Chapter 2

Chapter 2 Conditions Introduction In order to understand the distribution and abundance of a species we need to know its history (Chapter 1), the resources it requires (Chapter 3), the individuals’ rates of birth, death and migration (Chapters 4 and 6), their interactions with their own and other species | Chapter 2 Conditions Introduction In order to understand the distribution and abundance of a species we need to know its history Chapter 1 the resources it requires Chapter 3 the individuals rates of birth death and migration Chapters 4 and 6 their interactions with their own and other species Chapters 5 and 8-13 and the effects of environmental conditions. This chapter deals with the limits placed on organisms by environmental conditions. A condition is as an abiotic environmental factor that influences the functioning of living organisms. Examples include temperature relative humidity pH salinity and the concentration of pollutants. A condition may be modified by the presence of other organisms. For example temperature humidity and soil pH may be altered under a forest canopy. But unlike resources conditions are not consumed or used up by organisms. conditions may be altered - but not consumed For some conditions we can recognize an optimum concentration or level at which an organism performs best with its activity tailing off at both lower and higher levels Figure . But we need to define what we mean by performs best . From an evolutionary point of view optimal conditions are those under which individuals leave most descendants are fittest but these are often impossible to determine in practice because measures of fitness should be made over several generations. Instead we more often measure the effect of conditions on some key property like the activity of an enzyme the respiration rate of a tissue the growth rate of individuals or their rate of reproduction. However the effect of variation in conditions on these various properties will often not be the same organisms can usually survive over a wider range of conditions than permit them to grow or reproduce Figure . The precise shape of a species response will vary from condition to condition. The generalized form of response shown in Figure is appropriate for conditions like temperature and