Space Requirements 349 



Most species require more space than their physical dimensions. 

 The actual amount of room needed varies greatly from species to 

 species, but frequently the space required is very large either because 

 some necessity is sparse in its distribution or because of certain, often 

 poorly understood, psychological relations. A census of the fishes in- 

 habiting the shore zone of Morris Cove, New Haven, Conn, revealed 

 the presence of representatives of 32 species, but few specimens 

 longer than 100 mm were found. Although the adults of small species 

 were taken, only the young of the large species were present. The 

 depth of water was ample for more sizable fish to move about in, but 

 fish larger than the critical size were definitely excluded from this 

 habitat regardless of age although the mode of action of the space 

 requirement in this instance is not known (Warfel and Merriman, 

 1944). 



The manifestations of the space requirement may also occur in re- 

 lation to breeding, hostility, or other reaction. Insects such as the 

 Canna Leaf Roller (Calpodcs ethlius) have been found to breed sat- 

 isfactorily under laboratory conditions if placed in containers of cer- 

 tain size. They will not breed in smaller containers, nor in much 

 larger confined areas such as greenhouses, which appear to be other- 

 wise suitable. Cannibalism among insects often occurs when they 

 are crowded together, whereas members of the same species do not 

 attack, each other when they meet at other times under uncrowded 

 conditions. The English sparrow, a partially domesticated bird, will 

 breed regularly in large aviaries but will not breed in small cages. 

 The foregoing examples suffice to illustrate the point that definite 

 space requirements exist not only in relation to the physical needs of 

 the organism but also in relation to reactions essential in their life 

 cycles. 



For sessile forms, such as the majority of plants and non-motile 

 animals, the provision of minimum space is automatic to some extent. 

 As crowding continues to increase, competition brings about the 

 stunting and eventually the death of a portion of the population. 

 This process can be readily seen in the development of a stand of trees 

 from a bed of seedlings. Root competition, shading, and diseases 

 gradually thin out the population. Young white pines in New Eng- 

 land, for example, sprout from seeds to form a bed with a density of 

 perhaps 75,000 seedlings per hectare (30,000 per acre). When these 

 pines have attained an age of 60 to 80 years, they will form a mature 

 stand in which the density has been reduced by natural processes to 

 about 750 trees per hectare (300 per acre), or even less, without any 

 treatment by the forester. Similar examples may be found among 



