658 



ECOLOGY AND EVOLUTION 



theory coincided entirely with the values 

 observed. 



The competition between species for a 

 source of energy kept at a certain level 

 were investigated with Protozoa (Paratne- 



ments showed that the deficiency ot rooa 

 was the only limiting factor in these cases. 

 Under such conditions there existed a 

 competition of P. caudatum with P. aurelia 

 for the still unutilized food resources. After 



IMMIGRATIONS 



I I \^ \|f ^ 



PARAMECIUM CAUDATUM 



DIDINIUM NASUTUM y \ 



^A 



64 



^--A 



105 



_^--^-- 



18 



DAV 



Fig. 239. The eftect of exploitation and competition on populations of protozoans. Top, the 

 reciprocal relation of populations of Paramecium caudatum. and the predatory Didinium. 

 nasutum with controlled and simultaneous immigration of both species. Middle, the growth of 

 population volume of Paramecium caudatum alone in a controlled environment with a fixed 

 density of bacterial food at the beginning of the experiment compared with the population 

 volume of P. caudatum in competition with P. aurelia under the same conditions. Bottom, the 

 growth of population volume of P. aurelia alone and in competition with P. caudatum. (Re- 

 drawn from Gause, 1934a. ) 



cium caudatum and Paramecium aurelia). 

 These infusoria were cultivated in a 

 buffered, balanced Osterhout's salt solu- 

 tion (pH = 8.0), in which a suspension 

 was made of Bacillus pyocyaneus (of fixed 

 density). Bacteria do not multiply under 

 these conditions. Specially arranged experi- 



the source of energy had been utihzed a 

 redistribution of energy between two com- 

 ponents occurred which always resulted in 

 the complete ehmination of P. caudatum 

 by P. aurelia (Fig. 239). The correspond- 

 ing equations are somewhat complicated, 

 because the coeflScients of the struggle for 



