330 FOUNDATIONS OF BIOLOGY 



B. ADAPTATIONS TO THE LIVING ENVIRONMENT 



We have now discussed the close reciprocal relationship be- 

 tween organism and environment, putting emphasis upon 

 adaptations to the non-living surroundings, and must turn 

 more specifically to some striking interrelations of organism 

 with organism, in order to make possible an appreciation of 

 the devious means to which they have recourse to what ex- 

 tent the strands of the web of life become entangled in 

 the competition for a livelihood. 



The mutual biological interdependence of organisms is. in 

 the final analysis, the result of the primary demands of all 

 creatures proper food, habitat, reproduction, defense 

 against enemies and the forces of nature. The web of life 

 is an expression of the cooperation, jostling, and strife of 

 individual with individual, and species with species for these 

 primary needs; and the activities which follow from them 

 form the foundations of life in the lowest as well as the high- 

 est. There is a struggle for existence. A common food Fish, 

 the Squeteague, captures the Butter-fish or the Squid, which 

 in turn have fed on young Fish, which in their turn have fed 

 on small Crustacea, which themselves have utilized micro- 

 scopic Algae and Protozoa as food. Thus the food of the 

 Squeteague is actually a complex of all these factors, and 

 such a ' nutritional chain' is no stronger than its single links. 

 Circumstances which modify or suppress the food and there- 

 by reduce the abundance of the microflora and microfauna of 

 the sea are reflected in correlative changes in the abundance 

 of economically important food Fishes. And this same prin- 

 ciple is true throughout living nature, though only occasion- 

 ally is it possible to trace it. "Nature is a vast assemblage 

 of linkages." 



