CHAPTER 10 



POPULATION-HABITAT RELATIONSHIPS 



Habitat relationships refer to the manner in which 

 animals in a population interact and respond behaviorally and 

 biologically to characteristics of and changes in the 

 habitats /environments they occupy. These relationships, along 

 with direct human exploitation, constitute the 2 most 

 important factors involving wildlife management (Peek 1986). 

 They involve and integrate all aspects of habitat usage that 

 influence the occurrence, numbers, and dynamics of animals in 

 populations over time. Because of this, they inevitably also 

 involve questions such as "what is carrying capacity" and 

 "what ultimately regulates a population." 



For the last 50 years, management of most North American 

 ungulates has proceeded on the assumption that the amount of 

 forage available is the major factor influencing carrying 

 capacity and ungulate population size and dynamics. The 

 accompanying assumption has been that the number of ungulates 

 (density) is the major factor influencing forage quantity. 

 The herbivore-vegetation interaction determines carrying 

 capacity and population dynamics. From this also developed 

 both the premise that deer and other ungulates if left alone 

 will overuse their forage resources thereby lowering the 

 "carrying capacity" (Caughley 1979), and the corollary that 

 they must be cropped below "K" (ecological carrying capacity) 

 to insure less time-lag fluctuations in the population and to 

 provide larger, healthier, more productive animals. These 

 assumptions resulted in the "principles" of compensatory 

 mortality and reproduction. 



A more developed discussion of the concept of carrying 

 capacity, its origins, and usages was presented previously in 

 the Introduction (Chapter 1). Data from our study area and 

 population indicated that relationships between habitat-forage 

 factors and deer population ecology and dynamics were much 

 more complex than we originally believed based on the concepts 

 and "principles" of deer biology applied in management at the 

 time the study began. 



Mule Deer-Forage Interactions 



Forage Quantity 



Our data documented extensive variation in the quantities 

 of forage produced and available to mule deer on the study 

 area. Over an 11-year period, 1976-1986, the quantity of 

 forbs produced varied by about 16-fold and that of grasses by 

 about 4.5-fold from the lowest year of production to the 

 highest. The production of 3 shrub species varied by more 



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