Natural hermits cannot live; the single plant or 

 animal is incapable of existing without other mem- 

 bers of its kind. There is a fundamental and absolute 

 minimum population size requirement for each spe- 

 cies to live in each environment. Even if a habitat is 

 favorable, a certain number of individuals must still 

 be present before a species can survive. This mini- 

 mum population possesses unique properties be- 

 yond those of any smaller group and constitutes the 

 basic synergistic unit that determines the ecology of 

 the species. In this ecology, or population dynamics, 

 the reactions of individuals are relatively insignificant 

 in the complex function of the vi'hole, that is, the suc- 

 cess or failure of one organism has little influence 

 upon its population. On the other hand, the spatial 

 relations and fluctuations of minimum or larger 

 groups are primary in any aspect of population suc- 

 cess (see Figure 18-2, a chapter summary). For this 

 reason, population dynamics is a phenomenon of 

 single species and their environment, or population 

 ecology; however, though the species alone is em- 

 phasized, this ecology includes principles developed 

 in the previous chapter. 



POPULATION ORIGIN 



Local populations constantly are being created and 

 destroyed by constructive and destructive forces. 



These antagonistic processes are analagous to those of 

 land forms. For populations, the constructive force is 

 bwtic potential, the ability to increase in numbers, 

 and the destructive force is environmental resistance. 

 Both are of primary importance in the origin, de- 

 velopment, and extinction of populations. In fact, 

 these antagonistic forces are fundamental to any as- 

 pect of population ecology. 



The origin of populations is best understood in 

 relation to geographic segments; however, groups of 

 a single species originate in two related ways, by 

 reproduction and movement. Reproduction starts a 

 new population whenever a single member or smaller- 

 than-minimum group of the same species gives rise to 

 a minimum unit. Movement, both passive and active, 

 also can produce populations. Passive movements are 

 those in which organisms are transported by the en- 

 vironment. For example, the transportation of in- 

 dividual organisms by wind can provide the reproduc- 

 tive nucleus for part of a single species to form a new 

 local aggregation. Active movements, those made by 

 the organisms themselves, can begin a new species 

 segment whenever one to a few members of the 

 species are "drawn" into an area. Therefore, popu- 

 lations can form in any place already occupied by a 

 subminimum species group by reproduction alone, or 

 in new localities if transportation is followed by 

 reproduction to minimum size. 



339 



