or density did not necessarily influence forage conditions, 

 deer condition, or mortality. 



Fawn Production and Survival in Relation to Density 



Although one school of thought suggests that predators 

 can control ungulate populations (Gasaway et al . 1983), the 

 most widely accepted hypothesis is that a weather-forage 

 complex regulates ungulate populations. This operates in a 

 density-dependent manner through feedback mechanisms affecting 

 fawn production and survival (Lack 1954, Caughley 1979, and 

 Peek 1980). The latter holds that as density increases, 

 increased demand for forage by ungulates ultimately has a 

 detrimental effect on forage plants; declining forage quantity 

 and quality subsequently lead to declining ungulate density. 

 Implicit in this relationship are constant feedback and 

 fluctuations in plant and animal components through which 

 rates of increase in both are determined by ungulate density, 

 assuming that everything else is equal. Because this system 

 operates through a feedback loop, the density-dependent effect 

 is often delayed. The existence of this density-dependent 

 system is most apparent through changes in juvenile production 

 and mortality because juvenile survival is most sensitive to 

 reduced food supply (Caughley 1977). 



Theories involving density-dependence have usually 

 assumed a more or less determinate carrying capacity (K) . 

 More recently, Caughley (1977) recognized that 

 density-dependence is most likely to operate in its purest 

 form in areas where environmental fluctuation is minimal. 

 Species or populations living in widely fluctuating 

 environments such as the Missouri River Breaks would be least 

 likely to exhibit density-dependent phenomena, but to date few 

 species or populations have been placed in this category 

 (Caughley 1977) . 



The data we collected over 28 years enabled us to examine 

 the question of density-dependent regulation for this central 

 Montana population and determine the extent to which variation 

 in fawn production and survival was density-dependent. 



Initial production of fawns ( f awn-at-heel ratios) during 

 1976-1987 was not significantly (P > 0.05) density-dependent 

 (Fig. 5.15), nor did the assumption of a 1-year lag effect 

 result in statistical significance. Little change in 

 fawn-at-heel ratio occurred until adult female numbers were 

 more than 750, when a sharp decline took place. However, the 

 decline which took place in 1984 and 1985 (Fig. 5. 15) may not 

 have been related to density and the same decline could occur 

 at any population level if an equally severe drought occured. 

 Conception and pregnancy are probably less costly in terms of 

 energy and resources than lactation, so initial production was 



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