CHAPTER III 

 ANIMAL INTER-RELATIONS 



THE completion of a thorough ecological survey 

 of a single fairly uniform habitat leaves us in 

 possession of a list of all the species living there. 

 As was pointed out in the last chapter, these lists 

 are characteristic for each kind of habitat in any one 

 area. That is, each kind of habitat has its distinc- 

 tive animal community living in it, this distinctive- 

 ness depending partly upon the ecological specializa- 

 tion of certain species, and partly on the greater 

 abundance or scarcity of the species. We also saw 

 that the list of species from any one area is a good 

 deal smaller than might be expected, and that the 

 number of species in such a community (not count- 

 ing the parasites or microscopic forms) often lies be- 

 tween sixty and a hundred and forty. In order that 

 the survey lists may be given a meaning, we have 

 to inquire now how this community is organized. 

 All animal communities are organized in a certain 

 way — that is, they have a certain structure. This 

 structure is fundamentally similar in very widely 

 different habitats, and it depends chiefly upon the 

 manner in which animals are inter-related ecologic- 

 ally. In analysing the list of animals from a com- 

 munity, in order to understand its structure and 

 organization, several different principles can be 

 used. 



First, it is convenient to separate the animals that 

 come out by day from those that come out by 



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