CHAPTER 12 



POPULATION REGULATION 



Thus far, we have discussed what the population did, how 

 it did it, and to a limited extent, why it did what it did. 

 We now concentrate more fully on the latter and the questions 

 of why the population behaved in the observed fashion, why 

 abundance varies from place to place, and why no population 

 increases without limit (fluctuates). In the context of 

 population ecology these are the essence of population 

 regulation or limitation. 



The population we studied displayed an initial growth 

 pattern (Fig. 4.7) that was similar to a "typical" logistic 

 growth curve, implying density-dependent processes. Indeed, 

 the 



representative of density-dependent 

 regulation. The key point, however, is that almost all the 

 theoretical work focuses on the initial "irruptive", logistic 

 growth phase. Subsequent fluctuations, if considered at all, 

 are passed off lightly as "minor" fluctuations about "carrying 

 capacity" (K). Seemingly, it is assumed that similar 

 processes operate within these fluctuations as within the 

 initial growth phase. 



Our data collection and mathematical tests occurred 

 entirely within the fluctuating phase of an established 

 population. What may be termed minor fluctuation by theorists 

 or mathematical ecologists is of major concern to population 

 managers. During 1972-77, for example, neither deer managers 

 nor hunters in eastern Montana were pleased with ongoing 

 "minor" fluctuations in mule deer numbers. Compensatory 

 reproduction and mortality (density-dependent processes) were 

 nowhere evident. Thus, the question was not what processes 

 operate in founding populations, but what determines 

 fluctuations of established populations. Fluctuations in 

 established populations might not result from density- 

 dependent regulation. If that is so, the implications to 

 management are entirely different than those inherent in 

 density-dependent regulation theory. 



Factors regulating populations can generally be placed 

 into 2 categories; intrinsic and extrinsic, though there are 

 variations and combinations (see Chapter 1). Proponents of 

 population regulation by intrinsic factors or processes hold 

 that there is self -regulation by the population that prevents 

 it from reaching densities where it harms or destroys its 

 resource base. Various intrinsic mechanisms, operating in a 

 variety of ways have been proposed—behavior , physiological 

 change, genetic selection. All key on population density as 



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