Chapter 4 Life, Death and Life Histories Introduction: an ecological fact of life In this chapter we change the emphasis of our approach. We will not be concerned so much with the interaction between individuals and their environment, as with the numbers of individuals and the processes leading to changes in the number of individuals. | Chapter 4 Life Death and Life Histories Introduction an ecological fact of life In this chapter we change the emphasis of our approach. We will not be concerned so much with the interaction between individuals and their environment as with the numbers of individuals and the processes leading to changes in the number of individuals. In this regard there is a fundamental ecological fact of life Nnow Nthen B - D 1 - E 4-1 This simply says that the numbers of a particular species presently occupying a site of interest Nnow is equal to the numbers previously there Nthen plus the number of births between then and now B minus the number of deaths D plus the number of immigrants I minus the number of emigrants E . This defines the main aim of ecology to describe explain and understand the distribution and abundance of organisms. Ecologists are interested in the number of individuals the distributions of individuals the demographic processes birth death and migration that influence these and the ways in which these demographic processes are themselves influenced by environmental factors. What is an individual Unitary and modular organisms Our ecological fact of life though implies by default that all individuals are alike which is patently false on a number of counts. First almost all species pass through a number of stages in their life cycle insects metamorphose from eggs to larvae sometimes to pupae and then to adults plants pass from seeds to seedlings to photosynthesizing adults and so on. The different stages are likely to be influenced by different factors and to have different rates of migration death and of course reproduction. individuals differ in their life cycle stage and their condition unitary organisms Second even within a stage individuals can differ in quality or condition . The most obvious aspect of this is size but it is also common for example for individuals to differ in the amount of stored reserves they possess. Uniformity amongst .
