conditions fluctuate independently of animal density and that 

 these fluctuations invalidate simple models. Thus, Caughley 

 (1977, p. 197) states: 



"The methods previously outlined for estimating MSY 

 can cope with only a moderate degree of year-to-year 

 fluctuation in a population's condition of life. 

 They will be adequate for most populations. Some 

 populations, however, have a boom and bust economy, 

 increasing when conditions are favorable and 

 crashing to low levels when the environment 

 deteriorates. In this category can be placed most 

 of the species of oceanic fish, and several 

 vertebrates of the northern tundra. 

 The simplifying assumption of a steady density, 

 which at best is a dangerous abstraction, almost 

 completely parts company with reality when applied 

 to a boom and bust population. ...In these 

 circumstances density and resources are seldom 

 balanced and one cannot be predicted with confidence 

 from the other." 



That caveat was further emphasized by Macnab (1985) in 

 stating "First, in extreme environments (e.g. arid and 

 semi-arid regions) vegetation growth and the recruitment and 

 mortality of large herbivores are highly variable, so that the 

 "equilibrium" is more a mathematical abstraction than an 

 operational reality. . . .This changes none of the theory, but 

 makes management more difficult." 



Similarly, McCullough (1984:p. 224) indicated that his 

 deterministic model for the George Reserve would not work well 

 where "environmental stochasticity is great relative to the 

 density-dependent response of the environment." McCullough 

 (1984) also stated that "one of the major problems confronting 

 the wildlife biologist or resource manager is the year-to- 

 year variation in habitat quality due to variable amounts of 

 precipitation, severity of winter, presence or absence of an 

 acorn crop, etc." In environmental variable areas, an ad hoc 

 strategy is necessary to annually adjust management in 

 response to environmental factors. However, McCullough 

 (1984:p. 225) stated that "Fortunately, most white-tailed deer 

 populations occur in relatively benign environments and 

 respond well to density-dependent management." 



Based on findings from our study, we generally agree with 

 the cautionary words of these authors. However, we disagree 

 when they indicate that the assumption of relatively stable 

 environmental conditions applies to most populations. Rather, 

 it seems likely that simplified models may work only for 

 absolutely stable environmental conditions and become 

 increasingly dangerous to apply as variation increases. What 



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