reproduction and survival were always dependent upon density 

 of the study population. Our findings plus those becoming 

 increasingly common in the literature indicate that 

 nutritional deficiencies are not always, or even often, 

 related to density in free-ranging populations. 



Many people (especially lay persons) have recognized that 

 substitution probably doesn't occur on a 1:1 basis. Early 

 management programs, however, in practice appeared to assume 

 100% substitution and guaranteed compensatory reproduction and 

 mortality at all densities and times. There was no database 

 to challenge those assumptions until hunting mortality rates 

 began to rise above natural mortality rates. 



Differences in interpretations about the importance of 

 compensation and substitution are also rooted in the inherent 

 characteristics of the species studied. In hindsight, it is 

 easy to understand some conclusions resulting from early 

 studies of insects, fish, and birds, all of which had high 

 annual or generational rates of natural mortality. Only 

 recently have long-term data become available for larger, 

 longer-lived species with relatively low rates of natural 

 mortality. 



For a game bird population with an annual mortality rate 

 of 50-80% in the absence of hunting and for which young of the 

 year are not selected against by hunters, a high proportion of 

 hunting mortality might be expected to substitute for other 

 mortality. Should the same degree of substitution be expected 

 for adult female mule deer in the Missouri River Breaks with 

 an average annual natural mortality rate of 7-8%? Obviously 

 not. Thus, the conclusions of early studies were safe until 

 relatively recent times, when hunting mortality began to 

 exceed natural mortality rates by a significant degree in more 

 and more places . 



The higher degree of substitution (compensation) likely 

 for game bird populations does not mean that additive effects 

 of hunting mortality can be ignored for these species. First, 

 game birds as well as deer must be considered as individuals. 

 Chances of natural mortality vary at least somewhat by sex and 

 age class as well as place of residence. Thus, even for a 

 species with an annual natural mortality rate of 70%, 

 substitution isn't 100% efficient all the way up to 70% hunter 

 mortality. At least some fraction is additive. Second, 

 similar to what occurred with big game populations (and 

 similarly still unrecognized) , harvest rates may be creeping 

 up to and exceeding the natural mortality rate in some 

 locations. If an "unexplained' crash occurs in some local 

 areas in the future, it may not all be explainable by loss of 

 habitat or bad weather. 



336 



