Population Dynamics and an Elementary Model

We can think of a population as a group of individuals of the same species, which live together at the same time and in the same place. This statement implies the coexistence of, and potential interaction or intercommunication between, all the members of the population, and that the population is distinctly defined in space. Space should be tied in to the biology and behavior of a species – for example, an acre is too small to study an elk population. The spatial element, which is implied in statements such as “the population of New York” or “the population of insects in a wheat field,” is very important because it delimits the geographic boundaries of the population system being considered. Although the boundaries are often drawn rather arbitrarily, they should, ideally, enclose a distinct population unit (a much more strict definition used by systematic biologists is presented in Note 2.1).

Our view of the population as a number of individuals with an average set of properties may leave some, including the authors of this book, with an uneasy feeling. The qualities of individual choice and action have been suppressed for the purpose of simplicity and tractability. However, until a systematic approach is developed which permits the expression of individual action, without the necessity of considering all possible individual variations and interactions, we must be satisfied with our present concept, or throw up our hands in despair.