14.0.1 14.2: A population perspective is necessary in ecology.

As we begin our study of population ecology, a subtle but critical shift in perspective is required. It is a shift from the individual to the population—a group of organisms of the same species living in a particular geographic region—as the primary focus. Most ecological processes cannot be observed or studied within an individual. Rather, they emerge when considering the entire group of individuals that regularly exchange genes in a particular locale (FIGURE 14-3).

As an example of how a population perspective is needed, consider the case of adaptations produced by natural selection. Genetic changes don’t occur within an individual. That is, a longer neck did not evolve in one individual giraffe. Instead, the genetic changes occurred within a population of giraffes over time. As a consequence of differential reproductive success among the individuals of a population with different neck lengths, there came to be more individuals with longer necks over time. Birth rates, death rates, and immigration and emigration rates are also features not of individuals but of populations.

In the next sections, we explore how populations grow, a question important both to the management of consumable natural resources—as in the lobster fisheries described above —and to the conservation of rare and endangered species.