GENEP^L DISCUSSION 379 



surplus of animals is excluded from the population to maintain steady- 

 numbers. What do the fisheries people think? 



G. V. Nikol'skii: In some cases an adaptive response to the food supply- 

 may be involved. Either density of population or availability of resources 

 may be an influence. In most cases the reasons for population increase cannot 

 be ascertained : changes in even the nature and rate of metabolism may be 

 involved. 



R. J. H. Beverton: 'Self-regulatory' is not a term to which fisheries 

 people have attempted to give a standard definition, and indeed I do not 

 think it is much used in fish population literature. But if any generally 

 applicable defmition can usefully be made — and I am not sure that it can — 

 it would seem to me to have to do with processes by which a tendency for 

 the size of the population to increase or decrease is opposed by factors which 

 are inherent in the population itself — in effect by intraspecific density- 

 dependent factors. 



J. G. Skellam : The present confusion in population dynamics is largely 

 due to inadequate definition. Personally, I find much of the literature 

 meaningless or even self-contradictory. Admittedly, all sciences appear at 

 some stage to have difficulty in giving definition to concepts which initially 

 appear intuitive, and this kind of confusion has even arisen in mathematics. 

 The use in population dynamics of such terms as oscillation and periodicity 

 is bewildering to the mathematician, who has used these terms in a rigorous 

 way for a long time. If ecologists intend that mathematicians take an interest 

 in their problems it is essential that some of their terminology be clarified. 

 It would be a substantial advance if only some of the most frequently used 

 terms could be defined objectively, freed as far as possible from theoretical 

 content or imphcation. 



M. Graham : Objective uses can in a few cases be found. * Self-regulatory' 

 could be restricted to cases hke that of cannibahsm where an organism 

 regulates its own species directly. Similarly processes of dispersal in which 

 surplus members of the population are driven out into marginal habitats 

 would provide an instance of a self-regulatory mechanism. 



J. G. Skellam: I am not satisfied by the definition of self-regulation 

 just given, or by the example. For it still remains to be proved that the 

 behaviour pattern in question (cannibahsm) does in fact regulate. Before we 

 defme 'self-regulation', should we not defme 'regulation'? 



A. Milne: Graham's example was really one of intraspecific competition, 

 and this is really the only self-regulating mechanism. But all these terms 

 have a very large theoretical component, from which, if objectivity is to be 



