374 GENERAL DISCUSSION 



tion, with a theoretical maximum of 99 per cent of the juveniles of each 

 generation, could be maintained without reducing the population of adults. 



Presumably it would be agreed that with most natural populations the 

 state of affairs must be somewhere between these two extremes. Some 

 fluctuate rather wildly and may be only intermittently regulated (cf. 

 Schwerdtfeger, 1958). Others seem more closely regulated but still with a 

 good deal of variation in response to environmental changes. 



To unravel all the significant processes influencing the abundance of any 

 particular population is difficult, slow work. Before this has been done, is 

 there any way of assessing to what extent a population is under the influence 

 of density-related processes? It has been suggested that such an assessment 

 could be made by testing experimentally the readiness with which the 

 population recovered from an artificially imposed reduction (cf. Nicholson, 



Time 



J 1 WW 



\ \ \ \ I \ 



lAAA 



Fig. 4. — (M. E. Solomon) : Population growth and exploitation — see text. 



1957; Hairston, 1957). In the field of exploitation, has not this very experi- 

 ment been performed whenever a population has been reduced by over- 

 exploitation and its powers of recovery observed? 



Moreover, exploitation studies offer other ways of assessing the degree of 

 regulation of a population. I propose to formulate some of them as questions 

 for discussion, in the hope that examples will be forthcoming. They can be 

 clarified by means of diagrams depicting the changing numbers of animals 

 in an imaginary population in a stable environment. 



Fig. 4a represents the curve of increase from small numbers to saturation 

 level, in the form of the familiar sigmoid (but not necessarily logistic). It 

 will be assumed that if the numbers are reduced to any level below saturation, 

 they will increase again (so long as there is no exploitation) according to this 

 curve. Fig. 4/j shows this and suggests recovery curves for populations 

 capable of different rates of recovery. Hence (Question i) : What have 



