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THE AMEBIC AX NATURALIST { [Vol. XL VIII 



area of the habitat for animals. It has been observed, 

 in an area in Michigan, that grasshopper species corre- 

 spond closely in local distribution with plant communities 

 (D). There is evidence that local distribution of ani- 

 mals is seldom promiscuous as a result of motility {D: 

 159). It appears also that the local variability of envi- 

 ronmental conditions within the area of the climatic plant 

 community is sufficiently great, usually, to supply all 

 necessary conditions for a large number of animals, so 

 that the limits of the plant community need not be 

 passed, ordinarily. 



contained, and coextensive with the plant community (D : 161). 



One of the problems of plant ecology has been the 

 differentiation of plant communities or associations. 

 Mere comparison of lists of species is not sufficient; rela- 

 tive abundance of various species must be considered as 

 well. Animal assemblages in contiguous areas must be 

 separated in the same way. Given two adjoining habitats 

 differing in plant population, it has been found that, in 

 addition to differences of animal species, 6 there are also 

 differences of relative abundance in those animal species 

 common to the two areas (D: 154, 167). 



The local area of a plant community is determined by 

 (1) local distribution of the physical environmental com- 

 plex, and (2) influence (competition, etc.) of adjoining 

 plant communities. Local area of the animal community 

 depends upon (1) local distribution of physical environ- 

 ment, and (2) local distribution of vegetational environ- 

 ment, the latter being uniform over the area of the plant 

 community. Contiguous areas differing in physical and 

 vegetational conditions will be expected to differ also in 

 animal population, in a degree comparable to that of the 

 differences in environmental conditions. 



Physical habitats, and plant communities, sometimes 

 alternate, sometimes intergrade; it is not unreasonable to 

 expect accompanying alternation or intergradation of 



