364 



GENERAL DISCUSSION 



200 



100 



Generations 



Fig. 2. — (G. C. Varley) : Figs. 2 and 2A show different methods of presenting the same information. 

 The total population curve (upper line of Fig. 2) is the sum of the partial population curves 

 for eggs, larvae, pupae and adults. Fig. 2a is a generation curve for the adults, in which the 

 total number reaching the adult stage in a generation is plotted against generation number. 



numbers will show variation possibly correlated with that year's egg produc- 

 tion and always well below the peak of numbers represented by the total eggs 

 laid. 



We must therefore separate: 

 (i) Total population curves of the whole species, including all stages, against 

 time. 



(2) Partial population curves in which the actual number of (say) adults is 

 plotted against time, and there are many observations during the life-span of 

 an individual. 



(3) Generation curves in which the total number of individuals reaching a 

 particular stage (e.g. larval or adult) in any generation is plotted against 

 generation number. No individual is counted more than once. 



M. E. Solomon: My diagrams do not show the ups and downs of 

 reproduction and juvenile mortality, only the numbers of adults. The fish 

 data I quoted could indeed be displayed better in a diagram like Varley's. 

 Mine show only the results of such relationships, or others, in terms of adult 

 numbers. 



W. T. Edmondson: I am worried about this averaging of populations : 

 how relevant is it to real biological conditions ? 



