occurred based on recruitment rates . Perhaps the most 

 important role of dispersal and emigration was to maintain 

 mule deer in vacant available habitat on and off the study 

 area and maintain genetic diversity. 



"Dispersal is increasingly viewed as having significant 

 demographic causes and consequences" in microtines (Lidicker 

 1985). Observations of the "fence effect" for at least 6 

 species of Microtus is evidence that dispersal prevents or 

 slows population growth as long as a dispersal sink is 

 available (Lidicker 1985). Thus, it is possible that some 

 conclusions regarding the effects of increasing density on 

 reproduction and mortality based on studies of deer in 

 enclosures (Kie et al. 1979, McCullough 1979, Ozoga et al . 

 1982b) may not be entirely applicable to a natural environment 

 where emigration is not impeded. In most studies of "penned" 

 deer, density reaches much higher levels than observed in 

 adjacent habitat where dispersal could act to keep densities 

 below levels that result in density-related nutritional and 

 social problems affecting reproduction and mortality. Similar 

 conclusions might be made about studies (Verme 1965, 1967, 

 1969) that "artificially" raise density by decreasing forage 

 quantity and quality of penned deer to levels "seldom 

 encountered by free-ranging whitetails" (Verme 1965). 



Klein and Strangaard (1972) observed that food did not 

 appear to directly regulate roe deer (Capreolus capreolus) 

 numbers in Denmark through malnutrition or starvation except 

 in situations where areas were fenced. Instead, they 

 indicated that dispersal by young animals kept roe deer 

 populations below densities where forage supplies become a 

 factor in population regulation. However, they also noted 

 that social factors controlling roe deer populations would not 

 apply to North American deer because the latter are not 

 territorial and deer habitats are relatively continuous with 

 no low density areas to absorb the dispersing surplus. We now 

 know that those assumptions were premature. Findings of Ozoga 

 et al. (1982a) and this study indicate that some North 

 American deer can be functionally territorial. Similarly, 

 many North American deer populations, especially in the west, 

 are surrounded or interspersed by marginal or low-density 

 habitat capable of absorbing dispersers . Until recently, the 

 potential impacts of functional territoriality and dispersal 

 have been ignored or underestimated. We suggest these impacts 

 must be further examined and considered in research and 

 management of free-ranging populations. 



Interaction of Reproduction and Mortality 



Our data (Chapters 5 and 6, Hamlin and Mackie 1987) 

 indicated that a condition cycle in females related to 

 reproduction may contribute to periodic low fawn recruitment 



311 



