372 GENERAL DISCUSSION 



population dynamics one should choose animals which do not show irrele- 

 vant properties such as phases of distribution. Too many studies are isolated 

 from their essential ecological context such as position in a food chain. 



I. A. McLaren : I would plead that it is not the phenomena of popula- 

 tion dynamics but the tools — the methods of analysis — which wiU provide 

 us with a common basis. 



J. G. Skellam : I consider that there is already a body of information 

 on comparative population dynamics, as for example the population 

 consequences of particular types of life history such as parasitism etc. (Cole, 

 1954). Many apparent differences are merely the result of vast variations of 

 time scale. I agree with McLaren that it is not the features of species but of 

 systems which should concern us; that is to say the relation between species. 

 Several people have spoken of populations regulating their own numbers 

 by reducing fertihty. There is nothing in the theory of natural selection 

 which could favour such behaviour. As Haldane (1932) showed no gene 

 which induces altruistic behaviour of this kind would survive. This means 

 that population regulation is not controlled from within. 



L. B. Slobodkin: (a) I suggest that what we cannot expect is a single 

 model or formula to apply to all species. Any model will depend firstly on 

 its mathematical form and secondly on the values of the functions in the 

 formula. What we can expect is that there wiU be a hmited range of such 

 functions and of such values. 



(b) The reply to Skellam's argument which I have put forward before is 

 that natural selection may not always favour the production of the greatest 

 number of children if this is associated with a lower number of grandchildren 

 — or great-grandchildren. This mechanism demands a labile environment 

 and a number of small, mainly isolated populations. If in such circumstances 

 there are many local extinctions the populations having the features produc- 

 ing more grandchildren would be the ultimate survivors. 



N. Waloff: In the desert locust the high mobility of the gregarious 

 phase results not only in dispersal but also in regulation by dispersion. 



In this connection, surely Chitty's 'aggression' mechanism of dispersion 

 must apply only to gregarious species ? 



D. H. Chitty: Tinbergen included purely chemical mechanisms under 

 dispersion. 



M. E. Solomon: Some insects are definitely very intolerant of their 

 own kind — for example grain weevils in a jar. This may even interfere 

 with successful mating. 



D. H. Chitty: Voles as a rule only show the reaction between strangers. 



