CHAPTER V 



NUMBERS : STATISTICS 



IT is convenient to consider problems of animal 

 numbers under two headings. The first, dis- 

 cussed in the present chapter, covers our knowledge 

 of the actual densities of numbers of various animals, 

 the Hmits to increase, local groupings or aggrega- 

 tions of numbers, and methods of studying measuring 

 and numbers in the field. This side of the popula- 

 tion problem we have called Statistics. The other 

 side of it is concerned with rates of increase, fluctua- 

 tions in numbers, and the relation of problems of 

 numbers to the environmental factors which influence 

 the population. This we have called comprehensively 

 Dynamics (Chapter VI). The statistics are what we 

 find out about animal populations at any one moment. 

 The dynamics introduce movements in time. The 

 diff'erence is something like that between the study 

 of morphology and the study of development, 

 between an instantaneous photograph and a moving 

 picture. The periodic censuses that an animal 

 ecologist carries out are to his science what the serial 

 sections are to the embryologist or unit photographs 

 to the cinematographer. 



It is obvious, then, that before we can begin to 

 draw any conclusions about numbers and the nature 

 of animal population problems we require adequate 

 census data to work with, just as ecological surveys 

 produce the elementary data for understanding the 

 organization of animal communities and the signi- 



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