THE GROWTH FORM OF POPULATIONS 



311 



garis. The fact that the curve fits such social 

 groups provides a significant extension of 

 its general applicability. 



A final illustration for natural populations 



of insects is the study by Davidson (1944) 

 on the growth of adult thrips {Thrips im- 

 aginis) living in roses. Since the curve 

 adds nothing to what has already been said, 



835 40 45 50 55 60 65 70 75 80 85 90 95 1900 5 10 15 20 25 30 35 



YEAR 

 Fig. 103. The logistic growth of the sheep population of South Australia. Annual rainfall in 

 inches appears as the lower chart. ( From Davidson. ) 



^ esoo 



c 

 o 

 ^ 2000 



o 



- 1500 



Q_ 

 LJ 



^ 1000 



(J) 



LJ- 500 - 



1814 '24 '34 '44 ""54 '64 '74 '84 '94 1904 '14 '24 '34 



YEAR 

 Fig. 104. The logisitic growth of the sheep population of Tasmania and the maintenance of 

 that population in a state of semiequilibrium. The circles are averages for five-year periods. 

 (From Davidson.) 



