Article IX. — An ()iiiif/i(i/oi/icii/ < 'ross-.sciildii of l/h'i/ois in 

 Autiinin. By S. A. Forbes. 



The subject of the relations of interaction between organ- 

 isms and their environment, animate and inanimate, whicli 

 goes by the name of ecology, may Ite studied with reference to 

 the welfare of species or to that of the general assemblage of 

 organisms to which the species lielong. The ecology of a spe- 

 cies is special ecology; that of the assemblage is a phase or di- 

 vision of general ecology — more or less general according to 

 the size and contents of the assemlilage considered. In special 

 ecology every ecological factor, every feature of the environ- 

 ment, is valued according to its importance to the species; in 

 general ecology the various ecological factors are valued ac- 

 cording to their significance in the general system of life. In 

 special ecology the species is the all-important, dominating- 

 center; in general ecology each species takes its api)ropriate. 

 place — dominant, important, subordinate, or insignificant — ^ac- 

 cording to its dynamic value as a part of the whole. 



Precise studies in animal ecology have heretofore been 

 made mainly in the special field, necessarily so in the beginning 

 since a knowledge of the ecology of species must precede that 

 of groups or assemblages of species. These special studies are, 

 however, merely preliminary to a general study of the dynamic 

 system of organic life as exhibited in its larger and more com- 

 plex units. Without the corrective and organizing influ- 

 ence of such a study of the system as a whole, our ideas of that 

 system must lie badly proportioned and correspondingly inad- 

 equate or misleading — a fact readily illustrated liy the state of 

 our knowledge and opinion respecting the ecological signifi- 

 cance of birds. 



To learn what we now know of the effects of the- activities 

 of birds has required much difficult, expert, time-consuming 

 study, especially of the details of their food, since it is iriainly 



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