236 



L. B. SLOBODKIN 



Fig. 8. — Growth efficiency contours as a function of cell concentration of the medium and 

 caloric content of the animals in D. pulex. Data from Armstrong (i960) — Ordinate — 

 Chlamydomonas concentration in thousands of cells per ml. Abseissa — caloric content 

 of Daphnia. 



effect of predation on standing crop. I have called this concept 'population 

 efficiency'. I believe it is new and must therefore be defined and analysed 

 with caution. 



A predator that is not concerned about the size of the prey population may 

 try to simply maximize his yield per unit time, Y, or on a slightly more 

 sophisticated level may maximize ecological efficiency, E: 



-r 



W 



in which / is the energy consumed per unit time by the prey population. 

 A prudent predator may want to maximize the expression: 



Y 



£p = 



(-?) 



(3) 



