PREDATION AND EFFICIENCY IN LABORATORY 

 POPULATIONS 



L. B. Slobodkin 



Department of Zoology, The University of Michigan, Ann Arbor 



In an earlier Symposium Park (i955) said: 



'Research in laboratory population ecology should take its orientation 

 from some phenomenon known or suspected to occur in nature and 

 known or suspected to have significant ecological consequences. Its 

 objective is not to erect an indoor ecology but, rather, to illuminate 

 conceptually the general problem to which it is addressed. The research 

 is thus the handmaiden of field investigation; not the subsitute.' 

 Experimental populations can be thought of as analogue computers for 

 ecological problems. Their only advantage over purely mathematical models 

 is that the significant properties of the experimental animals are Ukely to be 

 things that would not occur to a mathematician. The corresponding dis- 

 advantage is that the results are more difficult to analyse than are those of 

 purely methematical theories and models. 

 I will be concerned with two aspects of population dynamics : 



1. The effect of predation on the number, size, and age distribution of 

 animals in a population. 



2. The efficiency with which yield to a predator is produced from a popula- 

 tion. 



While the discussion of hybrid populations has never been pubhshed a 

 series of papers have appeared on the Daphnia work (Slobodkin, 1954, 1959, 

 i960; Richman, 1958; Armstrong, i960). 



TECHNIQUES 

 The technique of all the experiments is essentially the same. A small container 

 is filled with a suitable fluid; artificial pond water in the case of hybrid 

 experiments, aged tap water in the case of the Daphnia. A feeding regimen 

 is set up under which some constant amount of suitable food is provided per 

 unit time. A few individuals of the appropriate species are added. These 

 animals and their descendants are called a population. The population is free 

 to multiply or die and to adjust itself to living in the experimental container. 



