GENERAL PROPERTIES OF POPULATIONS 



265 



Enough has been said about the formal, 

 yet supplementary, biological and statistical 

 attributes of the population. These features 

 are studied shortly as actual cases. 



DEFINITIONS, METHODS, AND SCOPE 



Definitions 



The word "population" is derived from 

 populus, meaning "people." It is commonly 

 used in two connotations, one concrete and 

 one abstract. Thus we can speak of a 

 chinch-bug population or the population of 

 the state of Kentucky, or we can refer to 

 the population theory of Malthus or Dou- 

 bleday. Certain formal definitions met in 

 the literature include: 



1. The whole number of people or in- 

 habitants in a country, section or area 

 ( Sociology ) 



2. The organisms, collectively, inhabiting an 

 area or region (Biology) 



3. "A group of living individuals set in a 

 frame that is limited and defined in re- 

 spect of both time and space" (Biology) 

 (Pearl, 1937) 



4. The entire group of organisms from 

 which samples are taken for measurement 

 (Biometry) 



Although general, these definitions in- 

 clude at least four distinct concepts. These 

 are number of individuals; likeness of kind 

 enumerated; aliveness; and limitation of 

 universe in space and time. Number of in- 

 dividuals, or enumeration, is an essential 

 theme in all population definitions. As 

 pointed out in the section on History, the 

 first question asked by the population stu- 

 dent is "How many?" To have meaning, 

 such a numerical statement must enumerate 

 kinds that have likeness. This gives the 

 statement dimensional homogeneitv. It 

 would be absurd to coimt all the "horses 

 and apples" in the state of Texas. Yet to 

 count the number of persons in Texas (or, 

 possibly, the number of apples) yields a 

 statistic of considerable meaning. Aliveness 

 suggests that any population definition deals 

 with organisms. We do not speak of the 

 "population of nuts and bolts in a fac- 

 tors'."" Aliveness is also suggested bv the 



• The term "population" is used frequentlv 

 by the statistician in two senses: (1) the entire 

 group of items from which a sample is taken: 

 12) the number of observations in any given 



very root, populus. Limitation in terms of 

 space and time means only that a popula- 

 tion must be defined in terms of a particu- 

 lar date or date-interval and a specific area 

 (or volume) exploited by the population. 

 When we define the population of New 

 York state, we mean the number of persons 

 in the area that is New York at some spe- 

 cified time or during some specified period. 

 As ecologists, we wish to extend the def- 

 inition to include more than one species. 

 We speak of such groups as "interspecies" 

 or "mixed populations" in contradistinction 

 to "intraspecies" populations. The genet- 

 icist and the student of speciation are pri- 

 marily concerned with a single species pop- 

 ulation, since at this level the genes are 

 assorted both quantitatively and qualita- 

 tively among the component organisms. The 

 ecologist. however, frequently meets in na- 

 ture an interacting system in which one 

 snecies population stands in some imme- 

 diate and functional relation to some other 

 .species population. This, an interspecies 

 phenomenon, then becomes a situation 

 to be analyzed within the total ecologi- 

 cal system. Some readers may argue with 

 cogency that a mixed species, interacting 

 group is in realitv a simple commimity. To 

 this we can replv onlv that the point is 

 worth consideration, and that, therefore, the 

 choice of terms mav become a matter of 

 arbitrarv definition. Personallv. we restrict 

 "communitv" to more comnlex natural 

 groupings and use "popiilation" for anv 

 single or mixed species association in the 

 laboratory or in nature that presents a 



statistical sample, indicated by IV (see Kurtz 

 and Edgerton, 1939.) These are connotations 

 not implied in our usage. Simpson and Roe 

 (1939) say, "Zoology is, or should be a study 

 of populations . . . The word 'population' in 

 this sense is not only literal, applying to a 

 natural assemblage of animals, but also figura- 

 tive, applying to all existing phenomena of 

 which a few are observed. Thus when specific 

 characters are determined from a sample, the 

 population is literal, the assemblage of all 

 animals of the species. When an individual's 

 behavior is studied, the population is figurative 

 and twofold: it is (1) the whole of the in- 

 dividual's behavior in this respect, before, 

 during, and after actual observation: and (2) 

 the behavior of all animals in which that be- 

 havior follows recognizably similar patterns." 

 (p. 166). 



