CHAPTER VIII 

 CROWDING AND INCREASED DEATH-RATE 



Measurements of growth, reproduction and length of hfe, sum up 

 many of the physiological processes that may be affected by crowd- 

 ing; the first two of these have already been considered in some de- 

 tail. These three functions are closely connected, and it has been 

 impossible to keep their treatment entirely separate. Thus, in the 

 preceding chapter, the discussion of the effect upon the rate of re- 

 production of confining Paramecia within a small capillary tube was 

 extended to include a partial discussion of such treatment upon the 

 longevity of the animals in order to get suflficient control of the avail- 

 able evidence to be able properly to evaluate factors affecting the 

 decrease in rate of reproduction brought about by crowding. 



Inspection of the material previously presented demonstrates that 

 the ability of adult organisms to live is not necessarily the same as 

 their ability to reproduce. Kuczynski (1928), in studying the bal- 

 ance of birth and deaths among the human population of Western 

 Europe, describes the differential effect of changing conditions upon 

 fertihty and upon the death-rate, and concludes that human fertility 

 has become a problem in itself largely divorced from the problem of 

 mortality. 



The experience of Warren that Daphnia lose their reproductive 

 capacity long before they die, and that in such a condition they may 

 be able to live through adverse conditions produced by overcrowding 

 and again take up reproduction when conditions become more favor- 

 able, is a case in point. Kalmus adds observations upon Paramecia 

 along the same line. The usual interaction between fertility and mor- 

 tality is such that in a given amount of liquid medium the popula- 

 tion increases to a maximum whose size depends on the volume of the 

 medium and the concentration of the food material, and then gradu- 

 ally falls to complete or nearly complete extinction. This course of 



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