Both Mackie (1978) for mule deer and Dusek et al. (1988) 

 for white-tailed deer have indicated that deer density 

 increased as the diversity, complexity, and stability of the 

 environment increased. Generally, the degree of topographic 

 relief, by itself, indicates the degree of diversity on an 

 area. Other aspects of diversity such as vegetation types, 

 microsites, and phenological development, follow from 

 topographic diversity. However, anything that increases 

 diversity, such as small agricultural fields, patchy or 

 variable grazing, or some fires, could also increase stability 

 and average deer density. 



Given the fixed-stable habitat constraints and the 

 morphological, physiological, and behavioral constraints 

 within which the population functions, "average" deer density 

 across the entire area is determined by the length of time 

 that dynamic-variable habitat conditions remain either 

 favorable or unfavorable. During favorable periods, deer can 

 survive and reproduce across most of the area. During 

 unfavorable conditions, most deer may not successfully 

 reproduce at all, and many adults living in marginal areas 

 die. This view is similar to that of Thompson (1929) and 

 Andrewartha and Birch (1954) in that the most important way in 

 which animal populations are limited is "by the shortage of 

 time when the rate of increase, r, is positive." That time is 

 never very long on environmentally variable areas like our 

 study area. 



Thus, our view is that there is a "balance" in the 

 dynamic-variable component of environment which interacts with 

 the fixed-stable habitat base and the animal component. This 

 interaction produces behavioral and biological responses in 

 individual animals that result in individual conseguences in 

 recruitment and mortality. The sum of these individual 

 conseguences is "population dynamics" (Fig. 1.4). 



This view contrasts with the traditional, popular, and 

 compelling ("it has to be true") concept of a "balance of 

 nature". The "balance of nature" view implies density- 

 dependent regulation involving a feedback loop between animals 

 and their food supply (herbivores and plants, carnivores and 

 prey ) . 



The "balance in the environment" view is unpopular 

 because it does not imply neat and tidy regulation. If the 

 environment fluctuates too widely or changes its character, 

 populations can become extinct, especially locally. We 

 maintain that this is precisely what has happened and 

 continues to happen. This is why viable populations exist in 

 some places and not in others and why species population 

 densities vary across their range. For the most part, 

 however, the environment fluctuates ("balances") within 



290 



