Ecology of Populations and Communities 15 



wind conditions would be entirely different from that produced by 

 widely spaced trees. The interdepend encies resulting from an aggre- 

 gation of individuals of the same species may become very complex, 

 as for example in an insect colony. The size of a population of ani- 

 mals or plants and its rate of growth are regulated by the reactions 

 of the members of the population to each other and to the environ- 

 ment. The study of these and similar relationships of groups of or- 

 ganisms is termed population ecology. 



When several species of plants and animals are present, as is usual 

 in a natural community, still further complications arise. In the 

 example cited above a very different vegetation would exist beneath 

 the 100 trees growing as isolated individuals from that found on the 

 floor of a dense grove. The species of animals associated with the 

 plants will also differ widely in the two situations. Widely varying 

 combinations of plants and animals coexist in the many different 

 habitats of the world. It is found that certain species live together 

 in mutual adjustment, and these are spoken of as a natural community. 

 The study of the relationships of the animals and plants making up a 

 community is termed community ecology or, again to use a coined 

 term, synecology. 



The development of the different viewpoints in ecology mentioned 

 above is due in part to the fact that the plant ecologist and the animal 

 ecologist have tended to work rather independently. The community 

 of plants is perhaps more obvious than the community of animals. 

 With plants the vegetation as a whole is often more striking, whereas 

 with animals the individuals tend to be considered first. Since animal 

 communities were generally less apparent, they were delineated at a 

 later date. The result of these influences was that animal and plant 

 communities were first thought of and studied quite separately. 



As ecology developed, it came to be realized'that the animals of an 

 area do not constitute a community entirely distinct from the plants 

 of that area. It is true that in some situations, as for example in the 

 desert, the interrelations between the animals and the plants may be 

 less critical than the dependence of both upon the physical factors of 

 the environment. Nevertheless, because of the fundamental depend- 

 ence of animals upon green plants and the influences commonly 

 effective in the reverse direction, the plants and animals of a region 

 should be considered as one integrated community. The animal 

 taxonomist lists the fauna in a region and the plant taxonomist records 

 the flora. The fauna and flora together are spoken of as the biota of 

 the region. In an analogous fashion the modern ecologist considers 

 the integrated community of plants and animals as the biotic com- 



