GENERAL DISCUSSION 3^9 



i.e. a climax situation — comparable for stability with the sea? If you are 

 not a pest entomologist, will you fmd more examples of instability on land 

 than will a marine biologist in the sea? 



M. E. Solomon: Instability of some terrestrial populations seems not to 

 be due to human influence. For example, it is probable that epidemics of the 

 spruce budworm in Canada have always been associated with the maturing 

 of large areas of balsam fir (Greenbank, 1956 and references therein). 



M. J. Way : I agree with Le Cren that most entomologists concentrate 

 on species tending to oscillate violently owing to human modification of 

 their habitat to the benefit of a particular species. Climatic changes are, 

 however, unlikely to cause a downward trend in a well-adapted animal. 

 Tropical forest environments are nearest to the sea among terrestrial areas in 

 their constancy: in temperate zones seasonal cycles, reflected in population 

 cycles mediated, for example, by diapause will cause some tendency to 

 unbalance. 



M. E. Solomon: But can it be shown that non-pest species do not 

 fluctuate ? 



E. Broadhead : Often the rarer species are not studied. 

 E. B. Worthington: Tsetse-fly may maintain a constant area of occupa- 

 tion in their environment but their abundance within it may fluctuate 

 widely. I can think of no single land environment with any degree of 

 stabihty. Aquatic biology is hence easier to tackle and fisheries workers can 

 draw straight lines. Land ecologists are generally behind the aquatic workers 

 in progress as a result. 



S.J. Holt: I wonder if it is really true that aquatic species don't fluctuate. 

 What about the 'red tide' and analogous phenomenal outbreaks among 

 planktonic organisms ? 



E. B. Worthington: I defy anyone to produce curves for population 

 levels for any land animal comparable with those for fish. 



I. A. McLaren: Stability for a buflalo is not the same thing as stability 

 for a mouse. A cod, being large and long lived, is in this comparable with 

 a buffalo. 



L. M. Dickie: I suggest that there are differences related to the stabiHty 

 of the environment. Cause (1947), working with his experimental popula- 

 tions, suggested an inverse relationship between capacity for phenotypic 

 and genotypic variation. Consider the relationship between land and sea: 

 the former is more variable as an environment and has complex animals 

 showing more genotypic variation but perhaps less phenotypic which are 

 therefore more readily thrown into resonance-type oscillations. Marine 



