every 50 adult males assuming an approximate 1 male: 2 female 

 adult sex ratio. Without additional mortality, the highest 

 observed reproductive rate would result in a doubling of a 

 population of 100 adult females and 50 adult males (an 

 instantaneous growth rate of 0.69); at the lowest observed 

 reproductive rate, population growth would be only slightly 

 reduced to an instantaneous rate of 0.51. Because natural 

 mortality was low, averaging only 7.2% in years when females 

 were not hunted, the observed "reproductive restraint" 

 (including both intrinsic and extrinsic factors) was not, by 

 itself, sufficient to halt growth of the female population. 

 As is the case for most populations, substantial mortality of 

 fawns and greater than average mortality of adults must occur 

 to achieve a stable population. 



Other data on reproduction and age-specific mortality of 

 adult females also indicated that little, if any, effective 

 "reproductive restraint" was inherent in the population. 

 Essentially all adult females initially produced fawns at the 

 maximum rate their body condition allowed. A high rate of 

 initial production apparently is less costly than rearing 

 fawns (Short et al . 1969), and the initial effort can be 

 terminated prior to or during early lactation if necessary. 

 It also provided maximum opportunity for successful 

 reproduction during years when quality of habitat resources 

 for rearing fawns were good. 



In highly variable and unpredictable environments such as 

 our study area, the trait of initially producing maximum 

 numbers of fawns during all years apparently maximizes the 

 opportunity for females to pass on their genes. Recruitment 

 of fawns in alternate years (Mundinger 1981) or producing 

 fewer fawns during all years, are apparently not successful 

 strategies in this environment because these females are no 

 more successful than others in rearing fawns during years of 

 poor conditions. Such strategies of reproductive restraint 

 might be selected for in harsh, but stable and predictable 

 environments where conditions for fawn rearing are seldom 

 exceptionally good. 



The environment of our study population is not only 

 variable and unpredictable, but includes an effective natural 

 predator. Living conditions for deer can swing rapidly from 

 exceptionally good to exceptionally poor, and both favorable 

 and unfavorable conditions often prevail over several 

 consecutive years. In this situation, the best reproductive 

 strategy appears to be to initially produce young at maximum 

 rates each year to take advantage of favorable conditions for 

 recruitment as they occur. Given the relatively short 

 reproductive life of mule deer on the area, it seems most 

 adaptive for a female to have the maximum potential to respond 

 to good conditions, should they occur during her lifetime. 



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