282 



POPULATIONS 



sampling, over 50 per cent young folk un- 

 der twenty years and only 2.6 per cent old- 

 sters sixty-five or over. One hundred years 

 later, in 1950, the population will have in- 

 creased by 115 milUons, becoming large and 

 mature, with a predominance of men and 



teristic of human population studies are, ot 

 course, not available. 



In his 1938 book Bodenheimer includes 

 a chart, based on his own work, that shows 

 how age structure within a laboratory popu- 

 lation of Drosophila varies as the culture 



women in their twenties, thirties, and 

 forties. In addition, the young will have 

 decreased relatively and the old increased. 

 As time goes on we can confidently expect 

 these trends to continue; either to worsen 

 or improve, depending on the individual 

 point of view. 



waxes and wanes (Fig. 82). It is apparent 

 that, as in human populations, there are 

 many young flies in the early days of 

 growth and many older ones in the later 

 days. Although an arithmetical analysis of 

 the data is not practicable, the figure brings 

 out well this principle. 



AGE OF CULTURE 



I'ig. 82. Age distribution in a changing Drosophila melanogaster population. (From 



Bodenheimer. ) 



We agree with Bodenheimer's contention 

 (1938) that investigation of age distribu- 

 tion in populations is "... a greatly neg- 

 lected study in animal ecology." In these 

 pages we review briefly several illustrations 

 taken from invertebrate and vertebrate 

 populations. Data of the scope so charac- 



In a paper on the plaice of the Irish Sea, 

 W. C. Smith (1939) discusses the age- 

 structure of that natural population relative 

 to two ecological areas: inshore grounds 

 and spawning grounds. This is a purely 

 empirical study based on catching the fish 

 in trawl-nets and determining their age by 



