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WHAT IS A POPULATION?
Citation:
Munns Jr., W R., W. N. Beyer, W. G. Landis, AND C. Menzie. WHAT IS A POPULATION? U.S. Environmental Protection Agency, Washington, DC, (5), 2002.
Description:
The word "population" has several meanings, a situation that can lead to confusion in risk assessments. A management goal "to protect wildlife populations," for example, might relate to populations as defined by population biologists, or it might mean simply to protect animals in general. Risk assessors should be aware, in particular, of the differences in meaning between popular and technical uses of the term. In popular usage, a population might refer to a group of organisms in a place at one time. Six robins in a backyard on a Tuesday describes such a population, and on Wednesday the population might be made up of different robins. In contrast, a more technical (or ecological) definition denotes that the group is a separate, self-regulating, local unit of interacting, conspecific organisms that remains coherent in time. This ecological use was well developed by 1949, when Alee et al. explained that a population not only has attributes that come from the organisms as individuals, but also has attributes that are unique to the group. Birth and death rates, age structure, and gene frequencies, as examples, do not apply to individuals, but provide useful ecological information about the group as a whole.
The ecological definition connotes separateness, that the organisms breed or otherwise interact more with individuals within the population than with those outside the population. The boundaries of a population are likely to be influenced by geography and other barriers, but are defined biologically by the distribution and interactions among individuals. The boundaries of a population defined in the popular sense may be drawn anywhere, such as around a Superfund site. Mayr (1963) recognized that actual populations deviate from the conceptual idea! and that they inter-grade with other populations. Similarly, Wilson (1999) conceded that "Few such objectively defined populations exist in nature." Local populations may be grouped together into larger, regional populations which, when combined, encompass the species. Some biologists find the concept of a metapopulation helpful, which is a group of loosely connected local populations that may continually become re-established or go extinct.