9 



Relations within 

 the Species 



Our discussion of nutrients in the previous chapter leads directly to 

 a consideration of the presence of other organisms as a part of the 

 environment. No individual animal could live by itself because it is 

 dependent upon other organisms for food as well as for other require- 

 ments. Certain green plants could conceivably exist in isolation for 

 a period, but, if the species is to be maintained, progeny must be 

 produced. The plant would soon be surrounded by young with 

 which it would be in competition, or in some other relation, so that 

 it would no longer be living as an isolated individual. As the popu- 

 lation of each species increases and as groups of animals and plants 

 are formed, new relations appear-in ecological situations as well as 

 in others the whole is more than the sum of its more obvious parts. 

 In this chapter we shall deal with intraspecific relationships and in the 

 next chapter with interspecific relationships. 



ORIGIN OF GROUPS 



Groups of individuals of the same species may arise in several ways: 

 (1) as the result of reproduction, (2) as the result of passive trans- 

 port, or (3) as the result of active locomotion. 



Reproduction 



Some groups are the result of the breeding activity of one breeding 

 unit-either an individual in the case of asexual reproduction, or a 

 pair in the case of sexual reproduction. If the progeny of this breed- 

 ing unit stay near together, a group will be formed. In some types 

 of animals and plants the young remain attached to the adults. This 

 situation is seen commonly in the cryptogamic plants, but instances 

 are also found among the higher plants. Strawberry plants, for ex- 



309 



