DESTRUCTION OF ONE SPECIES BY ANOTHER 



135 



The solution of this complicated equation 6 is represented on Figure 

 38. It is a further concretization for Paramecium and Didinium of 

 the principle of relaxation represented on Figure 34. An epidemic 



Nl(Otdiniuny)- 



Fig. 37. The interaction between Paramecium and Didinium at different 

 densities of population. The absence of the "residual growth" (comp. Fig. 36, 

 right) as well as the differences between both curves are connected with slightly 

 unfavorable conditions of the medium. 



of predators cannot start below the threshold in the concentration of 

 the prey, but above it we find usual relaxations. A characteristic 

 feature of our food-chain is an extraordinarily low value of the 

 threshold. 



6 The equation given by Gause and Witt ('35) is: 



dNi 



dt 



dm. 



dt 



= biNi - MNi) NiNt 



= b 2 N i VN l -f(N 2 ) iVi^O 



d 2 N 2 Ni = Oj 



(21c) 



