on increasing without limit, and the problem is to find out 

 what prevents unlimited increase in low-and high-density 

 populations. This is the problem of explaining fluctuations 

 in numbers . " 



The observation that no population increases without 

 limit and that substantial destructive or debilitating forces 

 were necessary to hold numbers in check was apparently the 

 original impetus behind the study of population regulation. 

 Malthus (as quoted by Davis 1950) believed that the ultimate 

 check was food, but the immediate check was "all those customs 

 and diseases generated by a scarcity of the means of 

 subsistence". Darwin (1872: p. 54) observed: "There is no 

 exception to the rule that every organic being naturally 

 increases at so high a rate, that if not destroyed, the earth 

 would soon be covered by the progeny of a single pair." 

 Although the works of Malthus and Darwin inspired the search 

 for methods of population regulation, most existing theories 

 were framed by the work of entomologists and a few fisheries 

 scientists from the early 1900s through the 1950s. 



Existing theory about pattern and process of population 

 regulation has generally developed around 4 schools of 

 thought. One of the earliest and, in some form, perhaps that 

 most widely held today, is often called the biotic school. 

 Although most commonly associated with Nicholson (1933), 

 Howard and Fiske (1911) had earlier promoted much the same 

 views. Nicholson believed that there was a balance in nature. 

 In order to achieve a state of balance, he stated it was 

 essential that a controlling factor should act more severely 

 at high densities and less severely at low densities. He 

 suggested that the chief "density-dependent" factor 

 controlling population level was intraspecif ic competition for 

 resources. Mathematical expression of this theory was 

 accomplished (Nicholson and Bailey 1935), but its assumptions 

 about the animals (l/N) and especially the environment 

 (constant) were viewed as unnatural by some (Milne 1957). 



A second school of thought developing during the same 

 period was that weather or climate was responsible for control 

 of populations (Uvarov 1931). Nicholson attempted to define 

 this school out of existence by stating that, because climate 

 was not affected by population density, it could not be a 

 controlling factor. He was really saying that weather 

 couldn't be a controlling factor because it did not meet his 

 assumption that only factors affected by population density 

 could control populations. Apparently, the possibility that 

 the effect of weather can vary with density was not considered 

 important. The density-dependent school of thought already 

 was so entrenched that the circular reasoning behind ruling 

 weather out as a controlling factor aroused little comment. 



