COMPETITION AND ECESIS 255 



Consequently competition is more intense ^vithin families than 

 within communities. 



269. Competition between different species. Competition is 

 closer between species of like form than between those that are 

 dissimilar. Such similarity between species is based upon the 

 form or nature of the plant body, and not upon systematic relation- 

 ship. Leaf, stem and root characters ordinarily determine the 

 outcome. The species most alike in these respects will be in 

 close competition, regardless of taxonomic relationship. This is 



Fig. 102. Competition between different species, in this case mountain 



daisies and grasses. 



equally true of species of the same genus, and of those belonging 

 to genera of widely separated families. This relation is expressed 

 l)v a second law of competition, viz., the closeness of the competition 

 between individuals of different species varies with their similarity 

 in vegetation form or hal^itat form. 



This law applies especially to the competition which arises 

 between occupants and invaders in the various stages of succes- 

 sion. Those invading species that show the greatest resemblance 

 to occupants in the form of leaf, stem, or root experience the 

 greatest difficulty in establishing themselves. On the contrary, 



