mortality consequences to the individual animal. The sum of 

 those individual strategies and consequences determine 

 population size, structure, behavior, and dynamics (Fig. 1.4). 

 The behavioral, physiological, recruitment, and mortality 

 submodels all contain both relatively stable and variable 

 components that interact with each other and with the habitat 

 model . 



Each component of the overall model (Fig. 1.4) can be 

 further subdivided with more detail. For instance, predation, 

 as part of the variable environment, includes such factors as 

 population level of coyotes, deer, and alternate prey; all the 

 natural factors affecting those populations (including 

 weather, livestock grazing, etc.); and the effect of humans 

 (predator control). 



No one factor can be said to be the ultimate factor 

 regulating the population. Interaction of factors is very 

 important. Overall, however, we believe that variable weather 

 interacting with the fixed habitat base is the ultimate factor 

 behind most changes in recruitment and mortality. Other 

 factors, such as predation, act as variable proximate factors 

 within the overall model. The removal of one or more 

 proximate factors such as predation, hunting, or emigration, 

 however, could result in observation of more "classical" 

 density-dependent population responses. 



The relative contribution of fixed-stable and dynamic- 

 variable components of the model to population characteristics 

 is illustrated by the 3 Montana mule deer populations 

 presented in Fig. 1.5. We propose that the fixed-stable 

 habitat base establishes potential population density (the 

 high) and explains why abundance varies from place to place. 

 The interaction of dynamic-variable habitat and population 

 components establishes the normal range of population density 

 below that potential and the actual position of the population 

 within that range at any given time. Thus, the dynamic- 

 variable components explain fluctuations in numbers within a 

 population. 



The data for our study population indicated that 

 interaction of a changing relative energy balance and 

 availability of permanent suitable habitat (space) limited its 

 growth. Food was only one part of the energy balance 

 equation. Density-independent fluctuation in weather was the 

 major factor influencing forage abundance and quality, energy 

 requirements, and deer population dynamics. There was little 

 or no feedback between deer density and forage abundance or 

 quality. Thus, although density-independent variation in 

 forage quantity and quality affected population growth, 

 seldom, if ever, did the population reach levels where 



20 



