GENERAL DISCUSSION 37i 



in favour of aggressive individuals (up to the point at which aggressive 

 behaviour occupies too much time and energy at the expense of other 

 biological demands), and it is to be expected that crowded populations differ 

 fundamentally from expanding populations in the frequency of certain 

 genotypes. 



A. Watson : Behaviour is recognized as important in birds, where it is 

 easy to see. It may also be of great significance in other species where it has 

 escaped notice because these are more difficult to watch. Trout might 

 provide an example, and be fairly easy to watch. Have the fisheries people 

 any data; 



E. D. Le Cren: There has been a lack of emphasis on behaviour studies 

 in much fisheries work simply because of the difficulty in observing the 

 animals. There are certainly evidences of changes and mass movements in 

 some species, such as herring, and of territorial behaviour in others such as 

 the trout. 



E. M. Nicholson: Changing distribution, and not only mortaUty, is 

 relevant here. 



D. Jenkins : Fish exist in a truly three-dimensional environment. This 

 may possible lead to major differences in their use of the habitat, as compared 

 with non-aquatic forms. 



M. Graham: Many fish can certainly inhabit levels in the habitat other 

 than that at which they are commonest. 



D. H. Chitty: I think the fishery results are of the greatest value, and 

 are in many aspects well ahead of those in terrestrial ecology. Le Cren's 

 point about behaviour is, however, important, suggesting that fisheries 

 workers may miss data vital to the understanding of population regulation 

 owing to technical difficulties. Only recently have we come near enough to 

 defining the points on which to look for detailed information. 



It is gratifying to find that work on one organism can be checked or 

 paralleled by work on another from an entirely different field. It is very 

 important that we try to arrange data so that hypotheses based on one species 

 can be tested on another. 



G. C. Varley: I think that workers with different taxonomic groups 

 make use of very different concepts; for example, where there is no overlap 

 in generations, as in many insects, problems of age distribution are enor- 

 mously simplified. Both the methods and the models used vary from group 

 to group, and before beginning a study it is essential to be clear as to what 

 model is begin proposed and what observations are required to test its 

 relevance. Thus, if one is looking for the common factors in comparative 

 25 



