gies in the broader context of their biological, 

 economic, and social consequences. 



DEER HERD SIMULATION MODEL 



A comprehensive flow chart of the compo- 

 nents and interrelationships of a deer herd was 

 developed. The available data did not permit 

 all relationships to be quantified and proxy 

 variables were devised to overcome this diffi- 

 culty. For other relationships a complete speci- 

 fication of the biological interactions would 

 have been possible, but this would have result- 

 ed in a model of substantial complexity. Model 

 building is a continual compromise between 

 abstraction and complexity. Models which 

 are too abstract are devoid of interest, and the 

 results will not be easily related to the oper- 

 ations of the real system. When the models 

 are large, and incorporate complex mathe- 



matical formulations, it can be difficult to 

 extract meaningful guidelines for management. 

 Such models may be expensive to run, and 

 thereby not achieve one objective of the model- 

 ing process, namely, to simulate the systems 

 and generate information and knowledge about 

 the systems at a cost less than alternative 

 analytical techniques. 



The flows and relationships identified for 

 the Mendocino County deer herd are sum- 

 marized in Figure 2. In this figure the time 

 series of events is not obvious. These are dis- 

 cussed in more detail later in the paper. The 

 model as depicted in Figure 2 is best viewed 

 as a summary of the most pertinent inter- 

 actions which occur each year in the deer 

 biomanagement system. The basic components 

 of the system are the birth and death process. 

 Each year fawns are born into the herd, and 

 the number of fawns born is a function of the 

 exponential average of the density in particular 



Habitat 

 Stracture 



fr 



— v,'eather 



Other factors, 

 geophysical, 



Ik 



Predators 



and 



Lisease 



Accidents and 

 unclaimed 

 hunter kill 



Competition 

 from wildlife 

 and domestic 

 animals 



)0<1 



I Source j 



.;];>/| Birth 

 ^ ^ Rate 



Legend 



Functional 



Relationships 



Causal Relationships 



Information Flows 



Real Flows (Deer) 



Deer Numbers 

 Age and Sex 

 (Density per 

 square mile) 



^^- 



Hunting 



Strategy by 

 Age, Sex, 

 Month at 

 Kill 



Regulation 

 and 



Management 



Figrure 2. — Biomanagement system of a deer population. 

 124 



