population increases beyond a certain point were not 

 measurable in core habitats. Much of the latter stages of 

 population increase occurred in marginal habitat. In like 

 manner, population declines generally occurred first and to 

 the greatest extent in habitats marginal to core area, thus, 

 trend areas that do not include marginal habitat may lack the 

 capability to provide early warning of true population trend. 



Age Structure and Sex and Age Ratios 



Age structure was not useful in predicting population 

 trends. It was most valuable in verifying past population 

 history. Age structure has often been considered very 

 important because it was easily collected at check stations, 

 and little, if any, data were collected on population size or 

 fawn recruitment. Often, the only information some states had 

 on fawn recruitment was data for past years based on age 

 structure of hunter-killed samples. Adequate sex and age 

 classifications and population estimates provide better data 

 for most management purposes than age structure from hunter- 

 killed samples. 



There are also other reasons, at least for populations in 

 variable environments, why age-structural data may not be as 

 useful to management as once thought. It has been commonly 

 assumed in wildlife management that a hunted population has a 

 younger age structure than an unhunted population. Similarly, 

 healthy, growing populations had a younger age structure than 

 unhealthy, high density populations. This was not necessarily 

 the case in the Missouri River Breaks. It apparently was also 

 not the case in some other northern Montana habitats . Data 

 from the mule deer population on the Brinkman Preserve, which 

 had been unhunted for many years (Rosgaard, unpubl. data), 

 indicated a younger age structure than our hunted population. 



The expectation that younger age structures occur in 

 hunted populations may be partially valid for populations with 

 stable recruitment rates. On average , hunted animals will not 

 live as long as unhunted animals. Thus, the average age of 

 adults should be less in hunted populations if recruitment is 

 stable. However, where recruitment rates vary considerably 

 from year to year, age structures may not differ measurably 

 between hunted and unhunted populations . 



A major reason why the assumption of a younger age 

 structure for hunted populations does not hold for variable 

 environments is its basis in the "principle" of compensatory 

 reproduction. Because fawn survival on our study area was not 

 directly related to number of deer in the population, a 

 reduction in numbers by hunting did not necessarily result in 

 increase fawn recruitment. Therefore, it was not surprising 

 that age structure of the female population on our study area 



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