390 



POPULATIONS 



knowledge exists about populations, it 

 should be possible to assemble this knowl- 

 edge in some form from which will emerge 

 a picture of population integrative mech- 



based on information gained from many 

 sources. It should be stressed also that the 

 diagram is merely a highly generalized, 

 illustrative tool and obviously not a com- 



POPULATION INTEGRATION 



(unfavorable climatic effects) 



DENSITY-INDEPENDENT 

 FACTORS 



I Population pressure due to 

 inter organismc contacts 

 2SpQtial restrictions 

 3.PredQtion pressures 

 4.Host parasite relations 

 5 Food restrictions 

 S.CertQin climatic effects 

 /Environmental conditioning 



DENSITY-DEPENDENT 

 FACTORS 



F' 



GENETIC FACTORS ^i: 



DECREASED REPRODUCTION 

 &/0R INCREASED MORTALITY - 

 OF HEREDITARY ORIGIN 



INCREASED REPRODUCTION 

 &/0R DECREASED MORTALITY 

 OF HEREDITARY ORIGIN 



GENETIC FACTORS 



^ECOLOGIC FACTORS 



("environmental resistance") 



EC0L06IC FACTORS 



DENSITY-INDEPENDENT DENSITY-DEPENDENT 

 FACTORS FACTORS 



(favorable climatic effects) (optimal crowding effects) 

 Fig. 138. A schematic representation of the interplay of factors that affect populations. 



anisms. Figure 138 is an elementary at- 

 tempt at such synthesis, and the discussion 

 following centers on this diagram. Nothing 

 unique is claimed for the figure, which is 



plete, detailed representation of popula- 

 tion factors and their interplay. 



It is to be noted that the figure has a 

 fundamental symmetry. The operations are 



