Because of their higher natural mortality rate, a greater 

 percentage of the hunting mortality of fawns substituted for 

 natural mortality than occurred with adult females. However, 

 the low hunting mortality rate of fawns resulted in little 

 realized substitution on a population basis. 



As a result of the above, the degree of substitution of 

 hunting mortality for natural mortality (compensation) in the 

 Breaks population probably varied quite widely. Substitution 

 may be greater at high densities or when natural mortality 

 rates are high. There may be almost no substitution when deer 

 numbers are low or deer are in excellent condition. The 

 degree of substitution also varies among sex and age classes 

 and among individuals within those classes. Again, when 

 analyzing all population processes, it is important to 

 recognize that deer are individuals (not l/N) . 



The impact of predators on the population can be viewed 

 similar to that of hunter harvest, although there are some 

 differences. Like hunting, the extent to which a predator 

 kill substitutes for other mortality will often also depend 

 upon the exact animal killed. In the Missouri River Breaks, 

 coyotes killed much higher proportions of fawns than did 

 hunters. Similarly, coyotes killed higher proportions of 

 older animals that were wounded, sick, or otherwise 

 predisposed to mortality. Thus, a higher proportion of the 

 deer killed by coyotes than by hunters substituted for losses 

 that would have resulted from malnutrition, old age, or 

 emigration. 



Not all mortality of deer by coyote predation substituted 

 for other mortality, however. Results of this and other 

 studies indicated that coyotes can and at times do kill 

 significant numbers of healthy deer that would have survived 

 in the absence of predation. The concept that predators kill 

 only the "doomed surplus" and do not cause population declines 

 is based on the erroneous assumption that reproduction always 

 produces more animals than the habitat will support. Clearly, 

 mule deer populations in the Missouri River Breaks were not 

 always near habitat fill, and predators did kill animals that 

 were not "doomed surplus". Similar to the effects of hunter 

 harvests, predation by coyotes appeared to have its greatest 

 impact when deer densities were low. This probably occurred 

 because there is little opportunity for substitution at low 

 densities (few vulnerable, old, etc.) nor can good nutritional 

 conditions and good fawn recruitment be guaranteed . 



Why do our conclusions differ from traditional views 

 about the occurrence and application of compensatory 

 reproduction and mortality? The "principles" of compensation 

 have generally been based, and especially applied, on the 

 assumption that nutritional deficiencies resulting in poor 



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